linux-kernel - Re: [syzbot] [net?] WARNING in skb_warn_bad

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Message-ID: <CANn89iKa8fyD2s1VdHJ2SQAUUzm-iPEXoKOGF6wvuqxofC4Frw@mail.gmail.com>
Date: Tue, 16 Jul 2024 07:54:00 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Sitnicki <jakub@...udflare.com>
Cc: Paolo Abeni <pabeni@...hat.com>, 
	syzbot <syzbot+e15b7e15b8a751a91d9a@...kaller.appspotmail.com>, davem@...emloft.net, 
	dsahern@...nel.org, kuba@...nel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, soheil@...gle.com, syzkaller-bugs@...glegroups.com, 
	willemb@...gle.com
Subject: Re: [syzbot] [net?] WARNING in skb_warn_bad_offload (5)

On Tue, Jul 16, 2024 at 3:17 AM Jakub Sitnicki <jakub@...udflare.com> 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 <jakub@...udflare.com>
> >> 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: syzbot+e15b7e15b8a751a91d9a@...kaller.appspotmail.com
> >> 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]