Re: [syzbot] [net?] WARNING in ipgre_xmit (2)

[Paolo Abeni]

On 8/11/26 3:13 PM, Jason Xing wrote:
> On Mon, Aug 10, 2026 at 6:54 PM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>> On 8/9/26 8:03 AM, Jason Xing wrote:
>>> On Wed, Aug 5, 2026 at 1:05 AM syzbot
>>> <syzbot+f16c1b285c9f63994eec@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>>
>>>> syzbot has found a reproducer for the following issue on:
>>>>
>>>> HEAD commit:    848acc8ffe1b Merge tag 'fsverity-for-linus' of git://git.k..
>>>> git tree:       upstream
>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=178fb649580000
>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4e38b15c29e6a1d9
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=f16c1b285c9f63994eec
>>>> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1617be32580000
>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d113b9580000
>>>>
>>>> Downloadable assets:
>>>> disk image: https://storage.googleapis.com/syzbot-assets/4949138dcfef/disk-848acc8f.raw.xz
>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/31cc6fbe5b8a/vmlinux-848acc8f.xz
>>>> kernel image: https://storage.googleapis.com/syzbot-assets/433919ca6520/bzImage-848acc8f.xz
>>>>
>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>> Reported-by: syzbot+f16c1b285c9f63994eec@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>>
>>>> ------------[ cut here ]------------
>>>> len > ((int)(~0U >> 1))
>>>> WARNING: ./include/linux/skbuff.h:2864 at pskb_may_pull_reason include/linux/skbuff.h:2864 [inline], CPU#1: syz-executor147/5638
>>>> WARNING: ./include/linux/skbuff.h:2864 at pskb_network_may_pull_reason include/linux/skbuff.h:3265 [inline], CPU#1: syz-executor147/5638
>>>> WARNING: ./include/linux/skbuff.h:2864 at pskb_inet_may_pull_reason include/net/ip_tunnels.h:481 [inline], CPU#1: syz-executor147/5638
>>>> WARNING: ./include/linux/skbuff.h:2864 at pskb_inet_may_pull include/net/ip_tunnels.h:486 [inline], CPU#1: syz-executor147/5638
>>>> WARNING: ./include/linux/skbuff.h:2864 at ipgre_xmit+0x958/0xcd0 net/ipv4/ip_gre.c:658, CPU#1: syz-executor147/5638
>>>> Modules linked in:
>>>> CPU: 1 UID: 0 PID: 5638 Comm: syz-executor147 Not tainted syzkaller #0 PREEMPT(full)
>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
>>>> RIP: 0010:pskb_may_pull_reason include/linux/skbuff.h:2864 [inline]
>>>> RIP: 0010:pskb_network_may_pull_reason include/linux/skbuff.h:3265 [inline]
>>>> RIP: 0010:pskb_inet_may_pull_reason include/net/ip_tunnels.h:481 [inline]
>>>> RIP: 0010:pskb_inet_may_pull include/net/ip_tunnels.h:486 [inline]
>>>> RIP: 0010:ipgre_xmit+0x958/0xcd0 net/ipv4/ip_gre.c:658
>>>> Code: 48 3b 84 24 80 00 00 00 0f 85 3b 01 00 00 31 c0 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d e9 3f 1a 78 01 cc e8 09 f5 6a f7 90 <0f> 0b 90 e9 08 f8 ff ff 44 89 ff 44 89 e6 e8 b5 f6 6a f7 45 39 e7
>>>> RSP: 0018:ffffc900039af5e0 EFLAGS: 00010293
>>>> RAX: ffffffff8a5c1d67 RBX: 0000000000000000 RCX: ffff888079535d00
>>>> RDX: 0000000000000000 RSI: 00000000ffffff40 RDI: 0000000000000000
>>>> RBP: ffffc900039af6b0 R08: ffff888079535d00 R09: 0000000000000002
>>>> R10: 0000000000004888 R11: ffffffff8a5c1410 R12: ffff88807ecbc000
>>>> R13: dffffc0000000000 R14: ffff88807b7f2780 R15: 00000000ffffff40
>>>> FS:  0000555590a0a400(0000) GS:ffff88812504b000(0000) knlGS:0000000000000000
>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> CR2: 000055704428ded0 CR3: 00000000788f2000 CR4: 00000000003526f0
>>>> Call Trace:
>>>>  <TASK>
>>>>  __netdev_start_xmit include/linux/netdevice.h:5400 [inline]
>>>>  netdev_start_xmit include/linux/netdevice.h:5409 [inline]
>>>>  __dev_direct_xmit+0x4b6/0x730 net/core/dev.c:4942
>>>>  __xsk_generic_xmit net/xdp/xsk.c:1253 [inline]
>>>>  xsk_generic_xmit+0x2759/0x47b0 net/xdp/xsk.c:1309
>>>>  __xsk_sendmsg net/xdp/xsk.c:1363 [inline]
>>>>  xsk_sendmsg+0x482/0x810 net/xdp/xsk.c:1373
>>>>  sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
>>>>  __sock_sendmsg net/socket.c:790 [inline]
>>>>  ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
>>>>  ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
>>>>  __sys_sendmsg net/socket.c:2770 [inline]
>>>>  __do_sys_sendmsg net/socket.c:2775 [inline]
>>>>  __se_sys_sendmsg net/socket.c:2773 [inline]
>>>>  __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
>>>>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>>>  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
>>>>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>> RIP: 0033:0x7fc137b1b409
>>>> Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 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 d8 ff ff ff f7 d8 64 89 01 48
>>>> RSP: 002b:00007fffc9ef46d8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>>>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc137b1b409
>>>> RDX: 0000000000000040 RSI: 0000200000000700 RDI: 0000000000000003
>>>> RBP: 0000000000000000 R08: 0000000080000000 R09: 0000000080000000
>>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>>>> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000003
>>>>  </TASK>
>>>>
>>>>
>>>> ---
>>>> If you want syzbot to run the reproducer, reply with:
>>>> #syz test: git://repo/address.git branch-or-commit-hash
>>>> If you attach or paste a git patch, syzbot will apply it before testing.
>>>>
>>>
>>> Please try this one instead. I'm not sure if the previous patch has
>>> the index problem...
>>>
>>> But the following patch can be applied in my tree.
>>>
>>> #syz test
>>
>> Please, do not cc the netdev ML for syzbot test patches. They may foul
>> PW and the KCI.
> 
> I see. Sorry for that.
> 
> But one more thing I have to ask is why the second attempt failed
> since I see no output from syzbot.
? I read:

"""
failed to apply patch:
error: corrupt patch at line 6
"""

in last message from syzbot, and a similar one in reply to the previous
attempt. You can use git format/git send-email even for syzbot tests, to
avoid this kind of problems

/P