[syzbot] [net?] kernel BUG in ip6gre_header (6)

[syzbot <syzbot+43a2ebcf2a64b1102d64@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    2061f18ad76e Merge tag 'caps-pr-20251204' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10cb0992580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=eaa3e2adda258a7
dashboard link: https://syzkaller.appspot.com/bug?extid=43a2ebcf2a64b1102d64
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e5dc1a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11fe021a580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-2061f18a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/28ad059bceaa/vmlinux-2061f18a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/747fcec76ac7/bzImage-2061f18a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+43a2ebcf2a64b1102d64@syzkaller.appspotmail.com

skbuff: skb_under_panic: text:ffffffff8a1d69a8 len:136 put:40 head:ffff888059bc7000 data:ffff888059bc6fe8 tail:0x70 end:0x6c0 dev:team0
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:213!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 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
Workqueue: mld mld_ifc_work
RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:213
Code: c7 e0 1a 6f 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 8e 94 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:ffffc900001b7280 EFLAGS: 00010282
RAX: 0000000000000087 RBX: dffffc0000000000 RCX: 98444bb9450e1700
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 00000000000006c0 R08: ffffc900001b6f87 R09: 1ffff92000036df0
R10: dffffc0000000000 R11: fffff52000036df1 R12: ffff88804ce8add0
R13: ffff888059bc7000 R14: ffff888059bc6fe8 R15: 0000000000000070
FS:  0000000000000000(0000) GS:ffff88808d683000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055555bb765c8 CR3: 000000001fd7c000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 skb_under_panic net/core/skbuff.c:223 [inline]
 skb_push+0xc3/0xe0 net/core/skbuff.c:2641
 ip6gre_header+0xc8/0x790 net/ipv6/ip6_gre.c:1371
 dev_hard_header include/linux/netdevice.h:3436 [inline]
 neigh_connected_output+0x286/0x460 net/core/neighbour.c:1618
 neigh_output include/net/neighbour.h:556 [inline]
 ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136
 __ip6_finish_output net/ipv6/ip6_output.c:-1 [inline]
 ip6_finish_output+0x234/0x7d0 net/ipv6/ip6_output.c:220
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247
 NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318
 mld_sendpack+0x8d4/0xe60 net/ipv6/mcast.c:1855
 mld_send_cr net/ipv6/mcast.c:2154 [inline]
 mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:213
Code: c7 e0 1a 6f 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 8e 94 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:ffffc900001b7280 EFLAGS: 00010282
RAX: 0000000000000087 RBX: dffffc0000000000 RCX: 98444bb9450e1700
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 00000000000006c0 R08: ffffc900001b6f87 R09: 1ffff92000036df0
R10: dffffc0000000000 R11: fffff52000036df1 R12: ffff88804ce8add0
R13: ffff888059bc7000 R14: ffff888059bc6fe8 R15: 0000000000000070
FS:  0000000000000000(0000) GS:ffff88808d683000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc5c02a230 CR3: 000000003b4e8000 CR4: 0000000000352ef0


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