Subject: Re: [syzbot] [net?] WARNING in skb_warn_bad_offload (5)

From: Jakub Sitnicki <[email-masked]>
Date: Tue, 23 Jul 2024 22:04:35 +0200

On Fri, Jul 19, 2024 at 09:34 PM +02, Jakub Sitnicki wrote:
> On Tue, Jul 16, 2024 at 07:54 AM -07, Eric Dumazet wrote:
>> On Tue, Jul 16, 2024 at 3:17 AM Jakub Sitnicki <[email-masked]> wrote:
>>>
>>> On Tue, Jul 16, 2024 at 12:04 PM +02, Paolo Abeni wrote:
>>> > On 7/16/24 03:23, syzbot wrote:
>>> >> syzbot found the following issue on:
>>> >> HEAD commit:    80ab5445da62 Merge tag 'wireless-next-2024-07-11' of git:/..
>>> >> git tree:       net-next
>>> >> console+strace: https://syzkaller.appspot.com/x/log.txt?x=175fb821980000
>>> >> kernel config:  https://syzkaller.appspot.com/x/.config?x=2dbcdd8641c4638f
>>> >> dashboard link: https://syzkaller.appspot.com/bug?extid=e15b7e15b8a751a91d9a
>>> >> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>>> >> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=172bf566980000
>>> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12fff535980000
>>> >> Downloadable assets:
>>> >> disk image: https://storage.googleapis.com/syzbot-assets/184da3869c30/disk-80ab5445.raw.xz
>>> >> vmlinux: https://storage.googleapis.com/syzbot-assets/85bfe9b60f21/vmlinux-80ab5445.xz
>>> >> kernel image: https://storage.googleapis.com/syzbot-assets/06064623a948/bzImage-80ab5445.xz
>>> >> The issue was bisected to:
>>> >> commit 10154dbded6d6a2fecaebdfda206609de0f121a9
>>> >> Author: Jakub Sitnicki <[email-masked]>
>>> >> Date:   Wed Jun 26 17:51:26 2024 +0000
>>> >>      udp: Allow GSO transmit from devices with no checksum offload
>>> >> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=142ccbed980000
>>> >> final oops:     https://syzkaller.appspot.com/x/report.txt?x=162ccbed980000
>>> >> console output: https://syzkaller.appspot.com/x/log.txt?x=122ccbed980000
>>> >> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> >> Reported-by: [email-masked]
>>> >> Fixes: 10154dbded6d ("udp: Allow GSO transmit from devices with no checksum offload")
>>> >> skb frag:     00000080: 62 3f 77 e4 0e 82 0d 2f 85 cc 44 ea 25 5a 99 76
>>> >> skb frag:     00000090: f2 53
>>> >> ------------[ cut here ]------------
>>> >> ip6tnl0: caps=(0x00000006401d7869, 0x00000006401d7869)
>>> >> WARNING: CPU: 0 PID: 5112 at net/core/dev.c:3293 skb_warn_bad_offload+0x166/0x1a0 net/core/dev.c:3291
>>> >> Modules linked in:
>>> >> CPU: 0 PID: 5112 Comm: syz-executor391 Not tainted 6.10.0-rc7-syzkaller-01603-g80ab5445da62 #0
>>> >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
>>> >> RIP: 0010:skb_warn_bad_offload+0x166/0x1a0 net/core/dev.c:3291
>>> >> Code: e8 5f 94 a3 f8 49 8b 04 24 48 8d 88 a0 03 00 00 48 85 c0 48 0f 44 cd 48 c7 c7 00 cc c5 8c 4c 89 f6 48 89 da e8 fb 92 ff f7 90 <0f> 0b 90 90 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 44 89 f9
>>> >> RSP: 0018:ffffc900034bedc8 EFLAGS: 00010246
>>> >> RAX: 7d287cad4185da00 RBX: ffff888040cdc0b8 RCX: ffff888023d1bc00
>>> >> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>>> >> RBP: ffffffff8cc5cbc0 R08: ffffffff815857b2 R09: fffffbfff1c39994
>>> >> R10: dffffc0000000000 R11: fffffbfff1c39994 R12: ffff888022880518
>>> >> R13: dffffc0000000000 R14: ffff888040cdc130 R15: ffff888040cdc130
>>> >> FS:  000055556e9e9380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
>>> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> >> CR2: 0000000020001180 CR3: 000000007c876000 CR4: 00000000003506f0
>>> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> >> Call Trace:
>>> >>   <TASK>
>>> >>   __skb_gso_segment+0x3be/0x4c0 net/core/gso.c:127
>>> >>   skb_gso_segment include/net/gso.h:83 [inline]
>>> >>   validate_xmit_skb+0x585/0x1120 net/core/dev.c:3661
>>> >>   __dev_queue_xmit+0x17a4/0x3e90 net/core/dev.c:4415
>>> >>   neigh_output include/net/neighbour.h:542 [inline]
>>> >>   ip6_finish_output2+0xffa/0x1680 net/ipv6/ip6_output.c:137
>>> >>   ip6_finish_output+0x41e/0x810 net/ipv6/ip6_output.c:222
>>> >>   ip6_send_skb+0x112/0x230 net/ipv6/ip6_output.c:1958
>>> >>   udp_v6_send_skb+0xbf5/0x1870 net/ipv6/udp.c:1292
>>> >>   udpv6_sendmsg+0x23b3/0x3270 net/ipv6/udp.c:1588
>>> >>   sock_sendmsg_nosec net/socket.c:730 [inline]
>>> >>   __sock_sendmsg+0xef/0x270 net/socket.c:745
>>> >>   ____sys_sendmsg+0x525/0x7d0 net/socket.c:2585
>>> >>   ___sys_sendmsg net/socket.c:2639 [inline]
>>> >>   __sys_sendmmsg+0x3b2/0x740 net/socket.c:2725
>>> >>   __do_sys_sendmmsg net/socket.c:2754 [inline]
>>> >>   __se_sys_sendmmsg net/socket.c:2751 [inline]
>>> >>   __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2751
>>> >>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>> >>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>>> >>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>> >> RIP: 0033:0x7f04f688fe89
>>> >> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 01 1a 00 00 90 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:00007ffeebc526e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
>>> >> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f04f688fe89
>>> >> RDX: 0000000000000001 RSI: 0000000020003cc0 RDI: 0000000000000003
>>> >> RBP: 00000000000f4240 R08: 0000000000000000 R09: 0000000000000001
>>> >> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffeebc52740
>>> >> R13: 00007f04f68dd406 R14: 0000000000000003 R15: 00007ffeebc52720
>>> >>   </TASK>
>>> >
>>> > Looking at the console log, the the relevant GSO packet is an UFO one with
>>> > CSUM_NONE. commit 10154dbded6d6a2fecaebdfda206609de0f121a9 only adjust the skb
>>> > csum for USO packets. @Jakub S. could you please have a look?
>>>
>>> Will do. Thanks for the hint.
>>
>> The trigger for the bug is the following :
>>
>> setsockopt(3, SOL_IPV6, IPV6_HOPOPTS,
>> "\0\3\0\0\0\0\0\0\5\2\0\0\0\1\0\302\4\200\0\0\0\5\2\0\6\302\4\0\0\0\1\302"...,
>> 40) = 0
>>
>> Some random IPV6_HOPTS, with multiple IPV6_TLV_JUMBO options
>>
>> Non GSO path sends a malformed packet just fine, but GSO complains loudly.
>>
>> (flowlabel 0x754ca, hlim 64, next-header Options (0) payload length:
>> 186) localhost > localhost: HBH
>> (pad1)(pad1)(pad1)(pad1)(pad1)(pad1)(rtalert: 0x0000)
>> (pad1)(padn)(jumbo: 2147483648 - payload len != 0) (rtalert: 0x0006)
>> (jumbo: 1 - already seen)  [|hbhopt]
>
> Thank you for the hint. Extracted a reproducer. Fix will follow.

Thanks for the patience.

I've got a fix to propose which pulls the gso_skb->ip_summed tweak added
to __udp_gso_segment() in commit 10154dbded6d ("udp: Allow GSO transmit
from devices with no checksum offload") from gso/udp code up to the udp
layer (udp[_v6]_send_skb()).

This warning can also be triggered for an ipv4 tunnel by turning off
csum offload (ethtool -K $tnl tx-checksum-ip-generic off). Will extend
udpgso.sh test to cover both v4 and v6.

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