[syzbot] [net?] WARNING in skb_attempt_defer_free

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3f0e9c8cefa9 Merge tag 'block-6.19-20251226' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12f11bb4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a11e0f726bfb6765
dashboard link: https://syzkaller.appspot.com/bug?extid=3e68572cf2286ce5ebe9
compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1545c89a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16e6089a580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-3f0e9c8c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9dd462c6c761/vmlinux-3f0e9c8c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cb19f02fe3f9/bzImage-3f0e9c8c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3e6857...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: net/core/skbuff.c:7243 at skb_attempt_defer_free+0x641/0x710 net/core/skbuff.c:7243, CPU#3: syz.0.20/6099
Modules linked in:
CPU: 3 UID: 0 PID: 6099 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:skb_attempt_defer_free+0x641/0x710 net/core/skbuff.c:7243
Code: 66 e6 f8 e9 5d ff ff ff e8 fc 8b 7c f8 90 0f 0b 90 e9 f0 fc ff ff e8 ee 8b 7c f8 90 0f 0b 90 e9 74 fc ff ff e8 e0 8b 7c f8 90 <0f> 0b 90 e9 95 fc ff ff e8 d2 8b 7c f8 90 0f 0b 90 48 b8 00 00 00
RSP: 0018:ffffc9000463f5a8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888053a2d180 RCX: ffffffff894256f5
RDX: ffff88802644a4c0 RSI: ffffffff89425a90 RDI: ffff888053a2d1e0
RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000001
R10: 0000000000000000 R11: ffff88802644aff0 R12: 0000000000000000
R13: 1ffff920008c7eb9 R14: 0000000000000000 R15: ffff888053a2d1d8
FS: 00007fad2f19c6c0(0000) GS:ffff8880d6bf5000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fad2f19bf98 CR3: 000000002ccfd000 CR4: 0000000000352ef0
Call Trace:
<TASK>
skb_consume_udp+0x19f/0x250 net/ipv4/udp.c:1854
udp_recvmsg+0x6c7/0x1350 net/ipv4/udp.c:2145
sk_udp_recvmsg+0x9b/0x120 net/ipv4/udp_bpf.c:20
udp_bpf_recvmsg net/ipv4/udp_bpf.c:94 [inline]
udp_bpf_recvmsg+0x5c0/0xe40 net/ipv4/udp_bpf.c:62
inet_recvmsg+0x625/0x6a0 net/ipv4/af_inet.c:891
sock_recvmsg_nosec net/socket.c:1078 [inline]
sock_recvmsg+0x1b2/0x250 net/socket.c:1100
____sys_recvmsg+0x218/0x6b0 net/socket.c:2812
___sys_recvmsg+0x114/0x1a0 net/socket.c:2854
do_recvmmsg+0x2fe/0x750 net/socket.c:2949
__sys_recvmmsg net/socket.c:3023 [inline]
__do_sys_recvmmsg net/socket.c:3046 [inline]
__se_sys_recvmmsg net/socket.c:3039 [inline]
__x64_sys_recvmmsg+0x22a/0x280 net/socket.c:3039
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fad2e38f7c9
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:00007fad2f19c038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007fad2e5e6090 RCX: 00007fad2e38f7c9
RDX: 0000000000000001 RSI: 00002000000047c0 RDI: 0000000000000003
RBP: 00007fad2e413f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fad2e5e6128 R14: 00007fad2e5e6090 R15: 00007ffd88783058
</TASK>


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