[syzbot] [net?] kernel BUG in ipgre_header (3)

syzbot
2025-10-20T16:32:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 561c80369df0 Merge tag 'tty-6.16-rc1-2' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=114649a2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e143c1cd9dadd720
dashboard link: https://syzkaller.appspot.com/bug?extid=a2a3b519de727b0f7903
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1215b1a2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=106c01a2580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-561c8036.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0e51e7b3acac/vmlinux-561c8036.xz
kernel image: https://storage.googleapis.com/syzbot-assets/431bb38ff9e1/bzImage-561c8036.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a2a3b519de727b0f7903@syzkaller.appspotmail.com

skbuff: skb_under_panic: text:ffffffff8a12f557 len:1304825492 put:1304825396 head:ffff888044b36000 data:ffff887ff6ed528c tail:0x120 end:0x6c0 dev:team0
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:211!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted 6.16.0-syzkaller-12256-g561c80369df0 #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
Workqueue: mld mld_ifc_work
RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:211
Code: c7 40 f9 93 8c 48 8b 74 24 08 48 8b 54 24 10 8b 0c 24 44 8b 44 24 04 4d 89 e9 50 55 41 57 41 56 e8 5e 0d f5 ff 48 83 c4 20 90 <0f> 0b cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc900001b7418 EFLAGS: 00010286
RAX: 0000000000000097 RBX: dffffc0000000000 RCX: b46b6e5b0ea16b00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 00000000000006c0 R08: ffffc900001b7127 R09: 1ffff92000036e24
R10: dffffc0000000000 R11: fffff52000036e25 R12: ffff888043e08a10
R13: ffff888044b36000 R14: ffff887ff6ed528c R15: 0000000000000120
FS: 0000000000000000(0000) GS:ffff88808d211000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c004aec000 CR3: 0000000059814000 CR4: 0000000000352ef0
Call Trace:
<TASK>
skb_under_panic net/core/skbuff.c:221 [inline]
skb_push+0xc3/0xe0 net/core/skbuff.c:2601
ipgre_header+0x67/0x290 net/ipv4/ip_gre.c:895
dev_hard_header include/linux/netdevice.h:3412 [inline]
neigh_connected_output+0x286/0x460 net/core/neighbour.c:1619
neigh_output include/net/neighbour.h:547 [inline]
ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141
__ip6_finish_output net/ipv6/ip6_output.c:-1 [inline]
ip6_finish_output+0x234/0x7d0 net/ipv6/ip6_output.c:226
NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318
mld_sendpack+0x800/0xd80 net/ipv6/mcast.c:1860
mld_send_cr net/ipv6/mcast.c:2159 [inline]
mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2698
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:211
Code: c7 40 f9 93 8c 48 8b 74 24 08 48 8b 54 24 10 8b 0c 24 44 8b 44 24 04 4d 89 e9 50 55 41 57 41 56 e8 5e 0d f5 ff 48 83 c4 20 90 <0f> 0b cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc900001b7418 EFLAGS: 00010286
RAX: 0000000000000097 RBX: dffffc0000000000 RCX: b46b6e5b0ea16b00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 00000000000006c0 R08: ffffc900001b7127 R09: 1ffff92000036e24
R10: dffffc0000000000 R11: fffff52000036e25 R12: ffff888043e08a10
R13: ffff888044b36000 R14: ffff887ff6ed528c R15: 0000000000000120
FS: 0000000000000000(0000) GS:ffff88808d211000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c004af0000 CR3: 0000000000e16000 CR4: 0000000000352ef0

---
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