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netrom: Fix use-after-free caused by accept on already connected socket

PATCH Superseded Hyunwoo Kim 2 participants 7 messages Jan 21, 2023 – Jan 23, 2023

Subsystems (2)
Networking Network drivers

v1 of 4 Superseded Latest is v4 →

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Hyunwoo Kim

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#0 lore raw

PATCH 1/1 netrom: Fix use-after-free caused by accept on already connected socket

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the sk of the parent AF_NETROM socket. And here's where use-after-free can happen through complex race conditions:

```
                  cpu0                                                     cpu1
                                                               1. socket_2 = socket(AF_NETROM)
                                                                  listen(socket_2)
                                                                  accepted_socket = accept(socket_2)    // loopback connection with socket_1
       2. socket_1 = socket(AF_NETROM)
            nr_create()    // sk refcount : 1
          connect(socket_1)    // loopback connection with socket_2
            nr_connect()
            nr_establish_data_link()
            nr_write_internal()
            nr_transmit_buffer()
            nr_route_frame()
            nr_loopback_queue()
            nr_loopback_timer()
            nr_rx_frame()
            nr_process_rx_frame()
            nr_state3_machine()
            nr_queue_rx_frame()
            sock_queue_rcv_skb()
            sock_queue_rcv_skb_reason()
            __sock_queue_rcv_skb()
            __skb_queue_tail(list, skb);    // list : sk->sk_receive_queue

       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);
                                                               4. close(accepted_socket)
                                                                    nr_release()
                                                                    nr_write_internal(sk, NR_DISCREQ)
                                                                    nr_transmit_buffer()    // NR_DISCREQ
                                                                    nr_route_frame()
                                                                    nr_loopback_queue()
                                                                    nr_loopback_timer()
                                                                    nr_rx_frame()    // sk : socket_1's sk
                                                                    nr_process_rx_frame()  // NR_STATE_3
                                                                    nr_state3_machine()    // NR_DISCREQ
                                                                    nr_disconnect()
                                                                    nr_sk(sk)->state = NR_STATE_0;
       5. close(socket_1)    // sk refcount : 3
            nr_release()    // NR_STATE_0
            sock_put(sk);    // sk refcount : 0
            sk_free(sk);
          close(uaf_socket)
            nr_release()
            sock_hold(sk);    // UAF
```

KASAN report by syzbot:

```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +5 -0
index 6f7f4392cffb..dcfa606684d7 100644
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1
author
#1 lore raw
Quoted 193 lines · Hyunwoo Kim

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the sk of the parent AF_NETROM socket. And here's where use-after-free can happen through complex race conditions:

```
                  cpu0                                                     cpu1
                                                               1. socket_2 = socket(AF_NETROM)
                                                                  listen(socket_2)
                                                                  accepted_socket = accept(socket_2)    // loopback connection with socket_1
       2. socket_1 = socket(AF_NETROM)
            nr_create()    // sk refcount : 1
          connect(socket_1)    // loopback connection with socket_2
            nr_connect()
            nr_establish_data_link()
            nr_write_internal()
            nr_transmit_buffer()
            nr_route_frame()
            nr_loopback_queue()
            nr_loopback_timer()
            nr_rx_frame()
            nr_process_rx_frame()
            nr_state3_machine()
            nr_queue_rx_frame()
            sock_queue_rcv_skb()
            sock_queue_rcv_skb_reason()
            __sock_queue_rcv_skb()
            __skb_queue_tail(list, skb);    // list : sk->sk_receive_queue

       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);
                                                               4. close(accepted_socket)
                                                                    nr_release()
                                                                    nr_write_internal(sk, NR_DISCREQ)
                                                                    nr_transmit_buffer()    // NR_DISCREQ
                                                                    nr_route_frame()
                                                                    nr_loopback_queue()
                                                                    nr_loopback_timer()
                                                                    nr_rx_frame()    // sk : socket_1's sk
                                                                    nr_process_rx_frame()  // NR_STATE_3
                                                                    nr_state3_machine()    // NR_DISCREQ
                                                                    nr_disconnect()
                                                                    nr_sk(sk)->state = NR_STATE_0;
       5. close(socket_1)    // sk refcount : 3
            nr_release()    // NR_STATE_0
            sock_put(sk);    // sk refcount : 0
            sk_free(sk);
          close(uaf_socket)
            nr_release()
            sock_hold(sk);    // UAF
```

KASAN report by syzbot:

```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +5 -0
index 6f7f4392cffb..dcfa606684d7 100644
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1

Dear,

Looks like a patch was recently submitted for another use-after-free bug in netrom:
https://lore.kernel.org/all/[email protected]/

However, the connect -> accept bug I reported is unaffected by the above patch and still occurs.

Regards,
Hyunwoo Kim

#2 lore raw

PATCH 1/1 netrom: Fix use-after-free caused by accept on already connected socket

In reply to Hyunwoo Kim

Hi,

Thanks for the patch!

From:   Hyunwoo Kim <[email protected]>
Date:   Sat, 21 Jan 2023 07:08:59 -0800
Quoted 29 lines

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the sk of the parent AF_NETROM socket. And here's where use-after-free can happen through complex race conditions:
```

                  cpu0                                                     cpu1
                                                               1. socket_2 = socket(AF_NETROM)
                                                                  listen(socket_2)
                                                                  accepted_socket = accept(socket_2)    // loopback connection with socket_1
       2. socket_1 = socket(AF_NETROM)
            nr_create()    // sk refcount : 1
          connect(socket_1)    // loopback connection with socket_2
            nr_connect()
            nr_establish_data_link()
            nr_write_internal()
            nr_transmit_buffer()
            nr_route_frame()
            nr_loopback_queue()
            nr_loopback_timer()
            nr_rx_frame()
            nr_process_rx_frame()
            nr_state3_machine()
            nr_queue_rx_frame()
            sock_queue_rcv_skb()
            sock_queue_rcv_skb_reason()
Quoted 8 lines
            __sock_queue_rcv_skb()
            __skb_queue_tail(list, skb);    // list : sk->sk_receive_queue

       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);

Sorry, I didn't understand how this is populated by close(accepted_socket), especially how skb->sk is set as socket_1's sk.

Quoted 126 lines

4. close(accepted_socket) nr_release() nr_write_internal(sk, NR_DISCREQ)
nr_transmit_buffer() // NR_DISCREQ
nr_route_frame() nr_loopback_queue() nr_loopback_timer()
nr_rx_frame() // sk : socket_1's sk
nr_process_rx_frame() // NR_STATE_3
nr_state3_machine() // NR_DISCREQ
nr_disconnect() nr_sk(sk)->state = NR_STATE_0;
5. close(socket_1) // sk refcount : 3
nr_release() // NR_STATE_0
sock_put(sk); // sk refcount : 0
sk_free(sk);
close(uaf_socket)
nr_release()
sock_hold(sk); // UAF

```

KASAN report by syzbot:
```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 5 lines

```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

I'd add

Fixes 1da177e4c3f4 ("Linux-2.6.12-rc2")
Quoted 11 lines
Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +0 -0
index 6f7f4392cffb..dcfa606684d7 100644

net/netrom/af_netrom.c static int nr_listen(struct socket *sock, int backlog) · line 403

Quoted 4 lines
net/netrom/af_netrom.c +1 -0
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {

I guess the same issue happens for SS_CONNECTING (non-blocking connect()), so this should be

        if (sock->state != SS_UNCONNECTED) {

?

Same for the rose and x25 patches.
https://lore.kernel.org/netdev/20230122173957.GA99728@ubuntu/
https://lore.kernel.org/netdev/20230122170925.GA98061@ubuntu/

Thanks,
Kuniyuki

Quoted 9 lines
net/netrom/af_netrom.c +4 -0
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1
author
#3 lore raw

Hi,

Thank you for your review.

Quoted 38 lines · Kuniyuki Iwashima

Hi,

Thanks for the patch!

From:   Hyunwoo Kim <[email protected]>
Date:   Sat, 21 Jan 2023 07:08:59 -0800
Quoted 32 lines

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the
sk of the parent AF_NETROM socket. And here's where use-after-free
can happen through complex race conditions:
```
cpu0 cpu1
1. socket_2 = socket(AF_NETROM) listen(socket_2)
accepted_socket = accept(socket_2) // loopback connection with socket_1
2. socket_1 = socket(AF_NETROM)
nr_create() // sk refcount : 1
connect(socket_1) // loopback connection with socket_2
nr_connect()
nr_establish_data_link()
nr_write_internal()
nr_transmit_buffer()
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame()
nr_process_rx_frame()
nr_state3_machine()
nr_queue_rx_frame()
sock_queue_rcv_skb()
sock_queue_rcv_skb_reason()
__sock_queue_rcv_skb()
__skb_queue_tail(list, skb); // list : sk->sk_receive_queue

Quoted 8 lines
Quoted 5 lines
       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);

Sorry, I didn't understand how this is populated by close(accepted_socket), especially how skb->sk is set as socket_1's sk.

When calling close(accepted_socket), accepted_socket is currently in NR_STATE_3 state,
so nr_release() calls nr_write_internal(sk, NR_DISCREQ).
In a later flow, nr_rx_frame() is called, where nr_find_socket() is used to get socket_1's sk
from the global list nr_list (Because circuit_index and circuit_id used for search were index/id of socket_1's sk):

```
        sk = NULL;

        if (circuit_index == 0 && circuit_id == 0) {
                if (frametype == NR_CONNACK && flags == NR_CHOKE_FLAG)
                        sk = nr_find_peer(peer_circuit_index, peer_circuit_id, src);
        } else {
                if (frametype == NR_CONNREQ)
                        sk = nr_find_peer(circuit_index, circuit_id, src);
                else
                        sk = nr_find_socket(circuit_index, circuit_id);    // here
        }
```

And nr_process_rx_frame(), nr_state3_machine(), nr_disconnect() are executed sequentially, and nr_sk(sk)->state = NR_STATE_0; is executed, so the state of socket_1 sk becomes NR_STATE_0.

As a result, 5. In close(socket_1), the code of case NR_STATE_0: of nr_release() is executed to free the sk, and finally, by calling close(uaf_socket), UAF occurs by referring to the freed sk.

Quoted 157 lines
Quoted 128 lines

4. close(accepted_socket) nr_release() nr_write_internal(sk, NR_DISCREQ)
nr_transmit_buffer() // NR_DISCREQ
nr_route_frame() nr_loopback_queue() nr_loopback_timer()
nr_rx_frame() // sk : socket_1's sk
nr_process_rx_frame() // NR_STATE_3
nr_state3_machine() // NR_DISCREQ
nr_disconnect() nr_sk(sk)->state = NR_STATE_0;
5. close(socket_1) // sk refcount : 3
nr_release() // NR_STATE_0
sock_put(sk); // sk refcount : 0
sk_free(sk);
close(uaf_socket)
nr_release()
sock_hold(sk); // UAF

```

KASAN report by syzbot:
```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 5 lines

```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

I'd add

Fixes 1da177e4c3f4 ("Linux-2.6.12-rc2")
Quoted 11 lines
Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +0 -0
index 6f7f4392cffb..dcfa606684d7 100644

net/netrom/af_netrom.c static int nr_listen(struct socket *sock, int backlog) · line 403

Quoted 4 lines
net/netrom/af_netrom.c +1 -0
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {

I guess the same issue happens for SS_CONNECTING (non-blocking connect()), so this should be

Quoted 7 lines
        if (sock->state != SS_UNCONNECTED) {

?

Same for the rose and x25 patches.
https://lore.kernel.org/netdev/20230122173957.GA99728@ubuntu/
https://lore.kernel.org/netdev/20230122170925.GA98061@ubuntu/

you're right.
I will submit the fixed v2 patches.

Regards,
Hyunwoo Kim

Quoted 14 lines

Thanks,
Kuniyuki

Quoted 9 lines
net/netrom/af_netrom.c +4 -0
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1
#4 lore raw
From:   Hyunwoo Kim <[email protected]>
Date:   Mon, 23 Jan 2023 08:57:06 -0800
Quoted 71 lines

Hi,

Thank you for your review.

Quoted 38 lines · Kuniyuki Iwashima

Hi,

Thanks for the patch!

From:   Hyunwoo Kim <[email protected]>
Date:   Sat, 21 Jan 2023 07:08:59 -0800
Quoted 32 lines

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the
sk of the parent AF_NETROM socket. And here's where use-after-free
can happen through complex race conditions:
```
cpu0 cpu1
1. socket_2 = socket(AF_NETROM) listen(socket_2)
accepted_socket = accept(socket_2) // loopback connection with socket_1
2. socket_1 = socket(AF_NETROM)
nr_create() // sk refcount : 1
connect(socket_1) // loopback connection with socket_2
nr_connect()
nr_establish_data_link()
nr_write_internal()
nr_transmit_buffer()
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame()
nr_process_rx_frame()
nr_state3_machine()
nr_queue_rx_frame()
sock_queue_rcv_skb()
sock_queue_rcv_skb_reason()
__sock_queue_rcv_skb()
__skb_queue_tail(list, skb); // list : sk->sk_receive_queue

Quoted 8 lines
Quoted 5 lines
       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);

Sorry, I didn't understand how this is populated by close(accepted_socket), especially how skb->sk is set as socket_1's sk.

When calling close(accepted_socket), accepted_socket is currently in NR_STATE_3 state,
so nr_release() calls nr_write_internal(sk, NR_DISCREQ).
In a later flow, nr_rx_frame() is called, where nr_find_socket() is used to get socket_1's sk
from the global list nr_list (Because circuit_index and circuit_id used for search were index/id of socket_1's sk):

```
        sk = NULL;

        if (circuit_index == 0 && circuit_id == 0) {
                if (frametype == NR_CONNACK && flags == NR_CHOKE_FLAG)
                        sk = nr_find_peer(peer_circuit_index, peer_circuit_id, src);
        } else {
                if (frametype == NR_CONNREQ)
                        sk = nr_find_peer(circuit_index, circuit_id, src);
                else
                        sk = nr_find_socket(circuit_index, circuit_id);    // here
        }
```
Quoted 2 lines

And nr_process_rx_frame(), nr_state3_machine(), nr_disconnect() are executed sequentially, and nr_sk(sk)->state = NR_STATE_0; is executed, so the state of socket_1 sk becomes NR_STATE_0.

Right, but nr_process_rx_frame() just sends out NR_DISCACK for accepted_socket, and nr_disconnect() does not queue skb for socket_1 ?

IIUC, uaf_socket's sk is the same one with socket_1, but I'm wondering how the sk is queued up for socket_1's recv queue at 4.

Quoted 189 lines

As a result, 5. In close(socket_1), the code of case NR_STATE_0: of nr_release() is executed to free the sk, and finally, by calling close(uaf_socket), UAF occurs by referring to the freed sk.

Quoted 157 lines
Quoted 128 lines

4. close(accepted_socket) nr_release() nr_write_internal(sk, NR_DISCREQ)
nr_transmit_buffer() // NR_DISCREQ
nr_route_frame() nr_loopback_queue() nr_loopback_timer()
nr_rx_frame() // sk : socket_1's sk
nr_process_rx_frame() // NR_STATE_3
nr_state3_machine() // NR_DISCREQ
nr_disconnect() nr_sk(sk)->state = NR_STATE_0;
5. close(socket_1) // sk refcount : 3
nr_release() // NR_STATE_0
sock_put(sk); // sk refcount : 0
sk_free(sk);
close(uaf_socket)
nr_release()
sock_hold(sk); // UAF

```

KASAN report by syzbot:
```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 5 lines

```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

I'd add

Fixes 1da177e4c3f4 ("Linux-2.6.12-rc2")
Quoted 11 lines
Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +0 -0
index 6f7f4392cffb..dcfa606684d7 100644

net/netrom/af_netrom.c static int nr_listen(struct socket *sock, int backlog) · line 403

Quoted 4 lines
net/netrom/af_netrom.c +1 -0
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {

I guess the same issue happens for SS_CONNECTING (non-blocking connect()), so this should be

Quoted 7 lines
        if (sock->state != SS_UNCONNECTED) {

?

Same for the rose and x25 patches.
https://lore.kernel.org/netdev/20230122173957.GA99728@ubuntu/
https://lore.kernel.org/netdev/20230122170925.GA98061@ubuntu/

you're right.
I will submit the fixed v2 patches.

Regards,
Hyunwoo Kim

Quoted 14 lines

Thanks,
Kuniyuki

Quoted 9 lines
net/netrom/af_netrom.c +4 -0
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1
author
#5 lore raw
Quoted 73 lines · Kuniyuki Iwashima
From:   Hyunwoo Kim <[email protected]>
Date:   Mon, 23 Jan 2023 08:57:06 -0800
Quoted 71 lines

Hi,

Thank you for your review.

Quoted 38 lines · Kuniyuki Iwashima

Hi,

Thanks for the patch!

From:   Hyunwoo Kim <[email protected]>
Date:   Sat, 21 Jan 2023 07:08:59 -0800
Quoted 32 lines

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the
sk of the parent AF_NETROM socket. And here's where use-after-free
can happen through complex race conditions:
```
cpu0 cpu1
1. socket_2 = socket(AF_NETROM) listen(socket_2)
accepted_socket = accept(socket_2) // loopback connection with socket_1
2. socket_1 = socket(AF_NETROM)
nr_create() // sk refcount : 1
connect(socket_1) // loopback connection with socket_2
nr_connect()
nr_establish_data_link()
nr_write_internal()
nr_transmit_buffer()
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame()
nr_process_rx_frame()
nr_state3_machine()
nr_queue_rx_frame()
sock_queue_rcv_skb()
sock_queue_rcv_skb_reason()
__sock_queue_rcv_skb()
__skb_queue_tail(list, skb); // list : sk->sk_receive_queue

Quoted 8 lines
Quoted 5 lines
       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);

Sorry, I didn't understand how this is populated by close(accepted_socket), especially how skb->sk is set as socket_1's sk.

When calling close(accepted_socket), accepted_socket is currently in NR_STATE_3 state,
so nr_release() calls nr_write_internal(sk, NR_DISCREQ).
In a later flow, nr_rx_frame() is called, where nr_find_socket() is used to get socket_1's sk
from the global list nr_list (Because circuit_index and circuit_id used for search were index/id of socket_1's sk):

```
        sk = NULL;

        if (circuit_index == 0 && circuit_id == 0) {
                if (frametype == NR_CONNACK && flags == NR_CHOKE_FLAG)
                        sk = nr_find_peer(peer_circuit_index, peer_circuit_id, src);
        } else {
                if (frametype == NR_CONNREQ)
                        sk = nr_find_peer(circuit_index, circuit_id, src);
                else
                        sk = nr_find_socket(circuit_index, circuit_id);    // here
        }
```
Quoted 8 lines
Quoted 2 lines

And nr_process_rx_frame(), nr_state3_machine(), nr_disconnect() are executed sequentially, and nr_sk(sk)->state = NR_STATE_0; is executed, so the state of socket_1 sk becomes NR_STATE_0.

Right, but nr_process_rx_frame() just sends out NR_DISCACK for accepted_socket, and nr_disconnect() does not queue skb for socket_1 ?

IIUC, uaf_socket's sk is the same one with socket_1, but I'm wondering how the sk is queued up for socket_1's recv queue at 4.

As I understand it, you know that socket_1 and uaf_socket's sk are the same, but you're confused about how the accepted_socket's sk of number 4 is equal to socket_1's sk, am I correct?

The sk of socket_1 and the sk of accepted_socket are completely different. In the flow chart I made, socket_1 and uaf_socket have the same sk, socket_2 has distinct sk, and accepted_socket has distinct non-overlapping sk. (There are a total of three sks in the flowchart.)

The reason accepted_socket can refer to the sk of socket_1 in #4 is that ->your_index and ->your_id of the sk of accepted_socket point to the sk of socket_1. As explained before, this index/id is used to get the sk of socket_1.
(In flowchart #4, nr_process_rx_frame() is called using the sk of socket_1 retrieved from nr_list, rather than using accepted_socket's own sk)

Please let me know if I'm misunderstanding and giving a strange answer.

Quoted 191 lines
Quoted 191 lines

As a result, 5. In close(socket_1), the code of case NR_STATE_0: of nr_release() is executed to free the sk, and finally, by calling close(uaf_socket), UAF occurs by referring to the freed sk.

Quoted 157 lines
Quoted 128 lines

4. close(accepted_socket) nr_release() nr_write_internal(sk, NR_DISCREQ)
nr_transmit_buffer() // NR_DISCREQ
nr_route_frame() nr_loopback_queue() nr_loopback_timer()
nr_rx_frame() // sk : socket_1's sk
nr_process_rx_frame() // NR_STATE_3
nr_state3_machine() // NR_DISCREQ
nr_disconnect() nr_sk(sk)->state = NR_STATE_0;
5. close(socket_1) // sk refcount : 3
nr_release() // NR_STATE_0
sock_put(sk); // sk refcount : 0
sk_free(sk);
close(uaf_socket)
nr_release()
sock_hold(sk); // UAF

```

KASAN report by syzbot:
```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 5 lines

```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

I'd add

Fixes 1da177e4c3f4 ("Linux-2.6.12-rc2")
Quoted 11 lines
Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +0 -0
index 6f7f4392cffb..dcfa606684d7 100644

net/netrom/af_netrom.c static int nr_listen(struct socket *sock, int backlog) · line 403

Quoted 4 lines
net/netrom/af_netrom.c +1 -0
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {

I guess the same issue happens for SS_CONNECTING (non-blocking connect()), so this should be

Quoted 7 lines
        if (sock->state != SS_UNCONNECTED) {

?

Same for the rose and x25 patches.
https://lore.kernel.org/netdev/20230122173957.GA99728@ubuntu/
https://lore.kernel.org/netdev/20230122170925.GA98061@ubuntu/

you're right.
I will submit the fixed v2 patches.

Regards,
Hyunwoo Kim

Quoted 14 lines

Thanks,
Kuniyuki

Quoted 9 lines
net/netrom/af_netrom.c +4 -0
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1
#6 lore raw
From:   Hyunwoo Kim <[email protected]>
Date:   Mon, 23 Jan 2023 10:22:09 -0800
Quoted 80 lines · Kuniyuki Iwashima
Quoted 79 lines
From:   Hyunwoo Kim <[email protected]>
Date:   Mon, 23 Jan 2023 08:57:06 -0800
Quoted 71 lines

Hi,

Thank you for your review.

Quoted 38 lines · Kuniyuki Iwashima

Hi,

Thanks for the patch!

From:   Hyunwoo Kim <[email protected]>
Date:   Sat, 21 Jan 2023 07:08:59 -0800
Quoted 32 lines

If listen() and accept() are called on an AF_NETROM socket that has already been connect()ed, accept() succeeds in connecting. This is because nr_accept() dequeues the skb queued in sk->sk_receive_queue in nr_connect().

This causes nr_accept() to allocate and return a sock with the
sk of the parent AF_NETROM socket. And here's where use-after-free
can happen through complex race conditions:
```
cpu0 cpu1
1. socket_2 = socket(AF_NETROM) listen(socket_2)
accepted_socket = accept(socket_2) // loopback connection with socket_1
2. socket_1 = socket(AF_NETROM)
nr_create() // sk refcount : 1
connect(socket_1) // loopback connection with socket_2
nr_connect()
nr_establish_data_link()
nr_write_internal()
nr_transmit_buffer()
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame()
nr_process_rx_frame()
nr_state3_machine()
nr_queue_rx_frame()
sock_queue_rcv_skb()
sock_queue_rcv_skb_reason()
__sock_queue_rcv_skb()
__skb_queue_tail(list, skb); // list : sk->sk_receive_queue

Quoted 8 lines
Quoted 5 lines
       3. listen(socket_1)
            nr_listen()
          uaf_socket = accept(socket_1)
            nr_accept()
            skb_dequeue(&sk->sk_receive_queue);

Sorry, I didn't understand how this is populated by close(accepted_socket), especially how skb->sk is set as socket_1's sk.

When calling close(accepted_socket), accepted_socket is currently in NR_STATE_3 state,
so nr_release() calls nr_write_internal(sk, NR_DISCREQ).
In a later flow, nr_rx_frame() is called, where nr_find_socket() is used to get socket_1's sk
from the global list nr_list (Because circuit_index and circuit_id used for search were index/id of socket_1's sk):

```
        sk = NULL;

        if (circuit_index == 0 && circuit_id == 0) {
                if (frametype == NR_CONNACK && flags == NR_CHOKE_FLAG)
                        sk = nr_find_peer(peer_circuit_index, peer_circuit_id, src);
        } else {
                if (frametype == NR_CONNREQ)
                        sk = nr_find_peer(circuit_index, circuit_id, src);
                else
                        sk = nr_find_socket(circuit_index, circuit_id);    // here
        }
```
Quoted 2 lines

And nr_process_rx_frame(), nr_state3_machine(), nr_disconnect() are executed sequentially, and nr_sk(sk)->state = NR_STATE_0; is executed, so the state of socket_1 sk becomes NR_STATE_0.

Right, but nr_process_rx_frame() just sends out NR_DISCACK for accepted_socket, and nr_disconnect() does not queue skb for socket_1 ?

Quoted 6 lines
Quoted 2 lines

IIUC, uaf_socket's sk is the same one with socket_1, but I'm wondering how the sk is queued up for socket_1's recv queue at 4.

As I understand it, you know that socket_1 and uaf_socket's sk are the same, but you're confused about how the accepted_socket's sk of number 4 is equal to socket_1's sk, am I correct?

No. I'm not sure how close(accepeted_socket) populates socket_1's sk_receive_queue by a skb->sk with socket_1's sk so that uaf_socket has the same sk with socket_1.

Quoted 11 lines

The sk of socket_1 and the sk of accepted_socket are completely different. In the flow chart I made, socket_1 and uaf_socket have the same sk, socket_2 has distinct sk, and accepted_socket has distinct non-overlapping sk. (There are a total of three sks in the flowchart.)

The reason accepted_socket can refer to the sk of socket_1 in #4 is that ->your_index and ->your_id of the sk of accepted_socket point to the sk of socket_1. As explained before, this index/id is used to get the sk of socket_1.
(In flowchart #4, nr_process_rx_frame() is called using the sk of socket_1 retrieved from nr_list, rather than using accepted_socket's own sk)

I understand this, but to make "uaf_socket = accept(socket_1)" happen, we need to put a skb in socket_1's recv_q in 4. with the found sk.

As you said, 4. finds the sk by nr_find_socket() (as not listener) and ends up calling nr_process_rx_frame(), which does not queue the skb with the sk for socket_1's queue, right ?

In short, where is a skb created with socket_1's sk and queued for socket_1's recv_q ? We don't call sock_queue_rcv_skb() at 4.

Quoted 194 lines

Please let me know if I'm misunderstanding and giving a strange answer.

Quoted 191 lines
Quoted 191 lines

As a result, 5. In close(socket_1), the code of case NR_STATE_0: of nr_release() is executed to free the sk, and finally, by calling close(uaf_socket), UAF occurs by referring to the freed sk.

Quoted 157 lines
Quoted 128 lines

4. close(accepted_socket) nr_release() nr_write_internal(sk, NR_DISCREQ)
nr_transmit_buffer() // NR_DISCREQ
nr_route_frame() nr_loopback_queue() nr_loopback_timer()
nr_rx_frame() // sk : socket_1's sk
nr_process_rx_frame() // NR_STATE_3
nr_state3_machine() // NR_DISCREQ
nr_disconnect() nr_sk(sk)->state = NR_STATE_0;
5. close(socket_1) // sk refcount : 3
nr_release() // NR_STATE_0
sock_put(sk); // sk refcount : 0
sk_free(sk);
close(uaf_socket)
nr_release()
sock_hold(sk); // UAF

```

KASAN report by syzbot:
```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128

CPU: 0 PID: 5128 Comm: syz-executor564 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x461 mm/kasan/report.c:417
 kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:775 [inline]
 nr_release+0x66/0x460 net/netrom/af_netrom.c:520
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:371 [inline]
 ____kasan_kmalloc mm/kasan/common.c:330 [inline]
 __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:968 [inline]
 __kmalloc+0x5a/0xd0 mm/slab_common.c:981
 kmalloc include/linux/slab.h:584 [inline]
 sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
 sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
 nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
 __sock_create+0x359/0x790 net/socket.c:1515
 sock_create net/socket.c:1566 [inline]
 __sys_socket_create net/socket.c:1603 [inline]
 __sys_socket_create net/socket.c:1588 [inline]
 __sys_socket+0x133/0x250 net/socket.c:1636
 __do_sys_socket net/socket.c:1649 [inline]
 __se_sys_socket net/socket.c:1647 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5128:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 __cache_free mm/slab.c:3394 [inline]
 __do_kmem_cache_free mm/slab.c:3580 [inline]
 __kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
 sk_prot_free net/core/sock.c:2074 [inline]
 __sk_destruct+0x5df/0x750 net/core/sock.c:2166
 sk_destruct net/core/sock.c:2181 [inline]
 __sk_free+0x175/0x460 net/core/sock.c:2192
 sk_free+0x7c/0xa0 net/core/sock.c:2203
 sock_put include/net/sock.h:1991 [inline]
 nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
 __sock_release+0xcd/0x280 net/socket.c:650
 sock_close+0x1c/0x20 net/socket.c:1365
 __fput+0x27c/0xa90 fs/file_table.c:320
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xaa8/0x2950 kernel/exit.c:867
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x21c3/0x2450 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 5 lines

```

To fix this problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().

I'd add

Fixes 1da177e4c3f4 ("Linux-2.6.12-rc2")
Quoted 11 lines
Reported-by [email protected]
Signed-off-by Hyunwoo Kim <[email protected]>
---
 net/netrom/af_netrom.c | 5 +++++
 1 file changed, 5 insertions(+)
net/netrom/af_netrom.c +0 -0
index 6f7f4392cffb..dcfa606684d7 100644

net/netrom/af_netrom.c static int nr_listen(struct socket *sock, int backlog) · line 403

Quoted 4 lines
net/netrom/af_netrom.c +1 -0
@@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {

I guess the same issue happens for SS_CONNECTING (non-blocking connect()), so this should be

Quoted 7 lines
        if (sock->state != SS_UNCONNECTED) {

?

Same for the rose and x25 patches.
https://lore.kernel.org/netdev/20230122173957.GA99728@ubuntu/
https://lore.kernel.org/netdev/20230122170925.GA98061@ubuntu/

you're right.
I will submit the fixed v2 patches.

Regards,
Hyunwoo Kim

Quoted 14 lines

Thanks,
Kuniyuki

Quoted 9 lines
net/netrom/af_netrom.c +4 -0
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;
Signature · 1 line
2.25.1