Re: [syzbot] [net?] WARNING in ah6_output

[Charalampos Mitrodimas <charmitro@posteo.net>]

syzbot <syzbot+01b0667934cdceb4451c@syzkaller.appspotmail.com> writes:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    9e89db3d847f Merge tag 'linux-can-fixes-for-6.15-20250520'..
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=1476d1f4580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c3f0e807ec5d1268
> dashboard link: https://syzkaller.appspot.com/bug?extid=01b0667934cdceb4451c
> compiler:       Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/8b09322b598e/disk-9e89db3d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/23ed08e707b5/vmlinux-9e89db3d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/be78b62450e7/bzImage-9e89db3d.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+01b0667934cdceb4451c@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> memcpy: detected field-spanning write (size 40) of single field "&top_iph->saddr" at net/ipv6/ah6.c:439 (size 16)

This could be happening because

     memcpy(&top_iph->saddr, iph_ext, extlen)

tries to copy extension headers (40 bytes) into the IPv6 saddr field (16
bytes), when extension headers should be at

      (u8*)top_iph + sizeof(*top_iph)

if I'm not mistaken.

C. Mitrodimas

> WARNING: CPU: 0 PID: 8838 at net/ipv6/ah6.c:439 ah6_output+0xe7e/0x14e0 net/ipv6/ah6.c:439
> Modules linked in:
> CPU: 0 UID: 0 PID: 8838 Comm: syz.1.814 Not tainted 6.15.0-rc6-syzkaller-00173-g9e89db3d847f #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> RIP: 0010:ah6_output+0xe7e/0x14e0 net/ipv6/ah6.c:439
> Code: ff e8 36 80 9f f7 c6 05 bb 97 48 05 01 90 b9 10 00 00 00 48 c7
> c7 a0 56 7e 8c 4c 89 fe 48 c7 c2 00 59 7e 8c e8 a3 dc 63 f7 90 <0f> 0b
> 90 90 e9 b5 fe ff ff e8 74 e4 35 01 48 8b 4c 24 10 80 e1 07
> RSP: 0018:ffffc900049f70e0 EFLAGS: 00010246
> RAX: 3fffcb5d3bcc7c00 RBX: 0000000000000028 RCX: 0000000000080000
> RDX: ffffc9000ece1000 RSI: 00000000000052e8 RDI: 00000000000052e9
> RBP: ffffc900049f7250 R08: 0000000000000003 R09: 0000000000000004
> R10: dffffc0000000000 R11: fffffbfff1bba944 R12: dffffc0000000000
> R13: 1ffff9200093ee38 R14: ffff8881452e8800 R15: 0000000000000028
> FS:  00007fc3a1d2c6c0(0000) GS:ffff8881260c7000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000555569628808 CR3: 000000005cf4e000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  xfrm_output_one net/xfrm/xfrm_output.c:555 [inline]
>  xfrm_output_resume+0x2c55/0x6170 net/xfrm/xfrm_output.c:590
>  __xfrm6_output+0x2eb/0x1070 net/ipv6/xfrm6_output.c:103
>  NF_HOOK_COND include/linux/netfilter.h:303 [inline]
>  xfrm6_output+0x1c6/0x4f0 net/ipv6/xfrm6_output.c:108
>  ip6_send_skb+0x1d5/0x390 net/ipv6/ip6_output.c:1981
>  l2tp_ip6_sendmsg+0x1378/0x1870 net/l2tp/l2tp_ip6.c:661
>  sock_sendmsg_nosec net/socket.c:712 [inline]
>  __sock_sendmsg+0x19c/0x270 net/socket.c:727
>  ____sys_sendmsg+0x505/0x830 net/socket.c:2566
>  ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
>  __sys_sendmsg net/socket.c:2652 [inline]
>  __do_sys_sendmsg net/socket.c:2657 [inline]
>  __se_sys_sendmsg net/socket.c:2655 [inline]
>  __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fc3a0f8e969
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fc3a1d2c038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007fc3a11b6080 RCX: 00007fc3a0f8e969
> RDX: 0000000000000800 RSI: 0000200000000540 RDI: 0000000000000004
> RBP: 00007fc3a1010ab1 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 00007fc3a11b6080 R15: 00007ffc18a80a58
>  </TASK>
>
>
> ---
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