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

[Jason Xing]

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.
>

#syz test

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index XXXXXXX..XXXXXXX 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -1025,6 +1025,7 @@ static struct sk_buff
*xsk_build_skb_zerocopy(struct xdp_sock *xs,
  return ERR_PTR(err);

  skb_reserve(skb, hr);
+ skb_reset_network_header(skb);
  if (desc->options & XDP_TX_METADATA) {
  err = xsk_skb_metadata(skb, buffer, desc, pool, hr);
  if (unlikely(err)) {
@@ -1110,6 +1111,7 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,

  skb_reserve(skb, hr);
  skb_put(skb, len);
+ skb_reset_network_header(skb);

  err = skb_store_bits(skb, 0, buffer, len);
  if (unlikely(err))