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general protection fault in drr_qlen_notify

syzbot syzbot 1 participant 3 messages Jul 4, 2025

Subsystems (3)
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syzbot

author syzbot
#0 lore raw

Hello,

syzbot found the following issue on:

HEAD commit:    17bbde2e1716 Merge tag 'net-6.16-rc5' of git://git.kernel...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1533f770580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8b0724e6945b4773
dashboard link: https://syzkaller.appspot.com/bug?extid=15b96fc3aac35468fe77
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14044c8c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14840c8c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/62107140ac32/disk-17bbde2e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/72e5df2d1649/vmlinux-17bbde2e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e906bf8ebf5c/bzImage-17bbde2e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by [email protected]
Oops: general protection fault, probably for non-canonical address 0xdffffc000000000b: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000058-0x000000000000005f]
CPU: 1 UID: 0 PID: 5817 Comm: syz-executor457 Not tainted 6.16.0-rc4-syzkaller-00108-g17bbde2e1716 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:__list_del_entry_valid_or_report+0x20/0x200 lib/list_debug.c:49
Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 b8 00 00 00 00 00 fc ff df 41 54 55 53 48 89 fb 48 83 c7 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 8b 01 00 00 48 89 da 48 8b 6b 08 48 b8 00 00 00
RSP: 0018:ffffc9000410f2e8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000050 RCX: 1ffff1100f97af5c
RDX: 000000000000000b RSI: ffffffff898bef4c RDI: 0000000000000058
RBP: 0000000000000050 R08: 0000000000000005 R09: 0000000000000000
R10: 00000000000a0000 R11: 0000000000000001 R12: ffffffff8ce802e0
R13: 0000000000000058 R14: ffffffff8ce802c0 R15: ffff88807cbd7800
FS:  000055557a6d4380(0000) GS:ffff888124852000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001fc0 CR3: 00000000721d4000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __list_del_entry_valid include/linux/list.h:124 [inline]
 __list_del_entry include/linux/list.h:215 [inline]
 list_del_init include/linux/list.h:287 [inline]
 drr_qlen_notify+0x24/0x150 net/sched/sch_drr.c:238
 qdisc_tree_reduce_backlog+0x221/0x500 net/sched/sch_api.c:811
 pie_change+0x86e/0xe70 net/sched/sch_pie.c:204
 pie_init+0x364/0x470 net/sched/sch_pie.c:456
 qdisc_create+0x454/0xfc0 net/sched/sch_api.c:1324
 __tc_modify_qdisc net/sched/sch_api.c:1749 [inline]
 tc_modify_qdisc+0x12bb/0x2130 net/sched/sch_api.c:1813
 rtnetlink_rcv_msg+0x3c6/0xe90 net/core/rtnetlink.c:6953
 netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x53d/0x7f0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg net/socket.c:727 [inline]
 ____sys_sendmsg+0xa98/0xc70 net/socket.c:2566
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620
 __sys_sendmsg+0x16d/0x220 net/socket.c:2652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9cedcdb669
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd67f881b8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ffd67f88388 RCX: 00007f9cedcdb669
RDX: 0000000000004000 RSI: 0000200000000280 RDI: 0000000000000006
RBP: 00007f9cedd4e610 R08: 0000000000000004 R09: 00007ffd67f88388
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffd67f88378 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__list_del_entry_valid_or_report+0x20/0x200 lib/list_debug.c:49
Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 b8 00 00 00 00 00 fc ff df 41 54 55 53 48 89 fb 48 83 c7 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 8b 01 00 00 48 89 da 48 8b 6b 08 48 b8 00 00 00
RSP: 0018:ffffc9000410f2e8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000050 RCX: 1ffff1100f97af5c
RDX: 000000000000000b RSI: ffffffff898bef4c RDI: 0000000000000058
RBP: 0000000000000050 R08: 0000000000000005 R09: 0000000000000000
R10: 00000000000a0000 R11: 0000000000000001 R12: ffffffff8ce802e0
R13: 0000000000000058 R14: ffffffff8ce802c0 R15: ffff88807cbd7800
FS:  000055557a6d4380(0000) GS:ffff888124852000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001fc0 CR3: 00000000721d4000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	90                   	nop
   1:	90                   	nop
   2:	90                   	nop
   3:	90                   	nop
   4:	90                   	nop
   5:	90                   	nop
   6:	90                   	nop
   7:	90                   	nop
   8:	90                   	nop
   9:	90                   	nop
   a:	f3 0f 1e fa          	endbr64
   e:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  15:	fc ff df
  18:	41 54                	push   %r12
  1a:	55                   	push   %rbp
  1b:	53                   	push   %rbx
  1c:	48 89 fb             	mov    %rdi,%rbx
  1f:	48 83 c7 08          	add    $0x8,%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 8b 01 00 00    	jne    0x1bf
  34:	48 89 da             	mov    %rbx,%rdx
  37:	48 8b 6b 08          	mov    0x8(%rbx),%rbp
  3b:	48                   	rex.W
  3c:	b8                   	.byte 0xb8
  3d:	00 00                	add    %al,(%rax)

---
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author syzbot
#1 lore raw
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***

Subject: Re: [syzbot] [net?] general protection fault in drr_qlen_notify
Author: [email protected]

#syz test

net/sched/sch_api.c +2 -1
index c5e3673aadbe..c4ca8f3b820b 100644
@@ -817,7 +817,8 @@ void qdisc_tree_reduce_backlog(struct Qdisc *sch, int n, int len)
 		cops = sch->ops->cl_ops;
 		if (notify && cops->qlen_notify) {
 			cl = cops->find(sch, parentid);
-			cops->qlen_notify(sch, cl);
+			if (virt_addr_valid(cl))
+				cops->qlen_notify(sch, cl);
 		}
 		sch->q.qlen -= n;
 		sch->qstats.backlog -= len;
author syzbot
#2 lore raw
In reply to syzbot
syzbot has bisected this issue to:

syzbot has bisected this issue to:

commit 103406b38c600fec1fe375a77b27d87e314aea09

Author: Lion Ackermann <[email protected]>
Date:   Mon Jun 30 13:27:30 2025 +0000

net/sched: Always pass notifications when child class becomes empty

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10d66c8c580000
start commit:   17bbde2e1716 Merge tag 'net-6.16-rc5' of git://git.kernel...
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=12d66c8c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=14d66c8c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8b0724e6945b4773
dashboard link: https://syzkaller.appspot.com/bug?extid=15b96fc3aac35468fe77
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14044c8c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14840c8c580000
Reported-by [email protected]
Fixes 103406b38c60 ("net/sched: Always pass notifications when child class becomes empty")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection