Patch "flow_dissector: properly cap thoff field" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

flow_dissector: properly cap thoff field

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
flow_dissector-properly-cap-thoff-field.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Wed, 17 Jan 2018 14:21:13 -0800
Subject: flow_dissector: properly cap thoff field

From: Eric Dumazet <[email protected]>

[ Upstream commit d0c081b49137cd3200f2023c0875723be66e7ce5 ]

syzbot reported yet another crash [1] that is caused by insufficient validation of DODGY packets.

Two bugs are happening here to trigger the crash.

1) Flow dissection leaves with incorrect thoff field.

2) skb_probe_transport_header() sets transport header to this invalid thoff, even if pointing after skb valid data.

3) qdisc_pkt_len_init() reads out-of-bound data because it trusts tcp_hdrlen(skb)

Possible fixes :

- Full flow dissector validation before injecting bad DODGY packets in the stack.
This approach was attempted here : https://patchwork.ozlabs.org/patch/
861874/

- Have more robust functions in the core. This might be needed anyway for stable versions.

This patch fixes the flow dissection issue.

[1]

CPU: 1 PID: 3144 Comm: syzkaller271204 Not tainted 4.15.0-rc4-mm1+ #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:355 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:413
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:432
 __tcp_hdrlen include/linux/tcp.h:35 [inline]
 tcp_hdrlen include/linux/tcp.h:40 [inline]
 qdisc_pkt_len_init net/core/dev.c:3160 [inline]
 __dev_queue_xmit+0x20d3/0x2200 net/core/dev.c:3465
 dev_queue_xmit+0x17/0x20 net/core/dev.c:3554
 packet_snd net/packet/af_packet.c:2943 [inline]
 packet_sendmsg+0x3ad5/0x60a0 net/packet/af_packet.c:2968
 sock_sendmsg_nosec net/socket.c:628 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:638
 sock_write_iter+0x31a/0x5d0 net/socket.c:907
 call_write_iter include/linux/fs.h:1776 [inline]
 new_sync_write fs/read_write.c:469 [inline]
 __vfs_write+0x684/0x970 fs/read_write.c:482
 vfs_write+0x189/0x510 fs/read_write.c:544
 SYSC_write fs/read_write.c:589 [inline]
 SyS_write+0xef/0x220 fs/read_write.c:581
 entry_SYSCALL_64_fastpath+0x1f/0x96

---
 net/core/flow_dissector.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

@@ -492,8 +492,8 @@ ip_proto_again:
 out_good:
 	ret = true;
 
-	key_control->thoff = (u16)nhoff;
 out:
+	key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen);
 	key_basic->n_proto = proto;
 	key_basic->ip_proto = ip_proto;
 

@@ -501,7 +501,6 @@ out:
 
 out_bad:
 	ret = false;
-	key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen);
 	goto out;
 }
 EXPORT_SYMBOL(__skb_flow_dissect);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ipv6-fix-udpv6-sendmsg-crash-caused-by-too-small-mtu.patch queue-4.4/flow_dissector-properly-cap-thoff-field.patch queue-4.4/ipv6-ip6_make_skb-needs-to-clear-cork.base.dst.patch queue-4.4/dccp-don-t-restart-ccid2_hc_tx_rto_expire-if-sk-in-closed-state.patch queue-4.4/netfilter-restart-search-if-moved-to-other-chain.patch queue-4.4/net-qdisc_pkt_len_init-should-be-more-robust.patch