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

flow_dissector: properly cap thoff field

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: flow_dissector-properly-cap-thoff-field.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Jan 28 17:37:09 CET 2018

From: Eric Dumazet edumazet@google.com Date: Wed, 17 Jan 2018 14:21:13 -0800 Subject: flow_dissector: properly cap thoff field

From: Eric Dumazet edumazet@google.com

[ 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

Fixes: 34fad54c2537 ("net: __skb_flow_dissect() must cap its return value") Fixes: a6e544b0a88b ("flow_dissector: Jump to exit code in __skb_flow_dissect") Signed-off-by: Eric Dumazet edumazet@google.com Cc: Willem de Bruijn willemb@google.com Reported-by: syzbot syzkaller@googlegroups.com Acked-by: Jason Wang jasowang@redhat.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/flow_dissector.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -550,8 +550,8 @@ 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;

@@ -559,7 +559,6 @@ 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 edumazet@google.com are

queue-4.9/ipv6-fix-udpv6-sendmsg-crash-caused-by-too-small-mtu.patch queue-4.9/flow_dissector-properly-cap-thoff-field.patch queue-4.9/ipv6-ip6_make_skb-needs-to-clear-cork.base.dst.patch queue-4.9/dccp-don-t-restart-ccid2_hc_tx_rto_expire-if-sk-in-closed-state.patch queue-4.9/net-qdisc_pkt_len_init-should-be-more-robust.patch