linux-kernel - Re: [syzbot] [net?] kernel BUG in ipgre

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Message-ID: <6910ed5f.a70a0220.22f260.00c1.GAE@google.com>
Date: Sun, 09 Nov 2025 11:37:03 -0800
From: syzbot <syzbot+a2a3b519de727b0f7903@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	zlatistiv@...il.com
Subject: Re: [syzbot] [net?] kernel BUG in ipgre_header (3)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel BUG in ipgre_header

skbuff: skb_under_panic: text:ffffffff89db8e37 len:1318440572 put:1318440500 head:ffff88805841d040 data:ffff888009ac02cc tail:0x108 end:0x180 dev:team0
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:212!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 54 Comm: kworker/u4:4 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: ipv6_addrconf addrconf_dad_work
RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:212
Code: c7 20 10 6e 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 be 96 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:ffffc9000101f2f8 EFLAGS: 00010282
RAX: 0000000000000097 RBX: dffffc0000000000 RCX: 0329d406b208d700
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000180 R08: ffffc9000101f007 R09: 1ffff92000203e00
R10: dffffc0000000000 R11: fffff52000203e01 R12: ffff88805434e290
R13: ffff88805841d040 R14: ffff888009ac02cc R15: 0000000000000108
FS:  0000000000000000(0000) GS:ffff88808d75f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555771e9588 CR3: 0000000059800000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 skb_under_panic net/core/skbuff.c:222 [inline]
 skb_push+0xc3/0xe0 net/core/skbuff.c:2602
 ipgre_header+0x67/0x290 net/ipv4/ip_gre.c:895
 dev_hard_header include/linux/netdevice.h:3419 [inline]
 neigh_connected_output+0x286/0x460 net/core/neighbour.c:1619
 neigh_output include/net/neighbour.h:547 [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 include/linux/netfilter.h:318 [inline]
 ndisc_send_skb+0xbce/0x1510 net/ipv6/ndisc.c:512
 ndisc_send_ns+0xcb/0x150 net/ipv6/ndisc.c:670
 addrconf_dad_work+0xaae/0x14b0 net/ipv6/addrconf.c:4282
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 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:212
Code: c7 20 10 6e 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 be 96 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:ffffc9000101f2f8 EFLAGS: 00010282
RAX: 0000000000000097 RBX: dffffc0000000000 RCX: 0329d406b208d700
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000180 R08: ffffc9000101f007 R09: 1ffff92000203e00
R10: dffffc0000000000 R11: fffff52000203e01 R12: ffff88805434e290
R13: ffff88805841d040 R14: ffff888009ac02cc R15: 0000000000000108
FS:  0000000000000000(0000) GS:ffff88808d75f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033


Tested on:

commit:         f850568e Merge tag 'i2c-for-6.18-rc5' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15634b42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=486aa0235ebabcac
dashboard link: https://syzkaller.appspot.com/bug?extid=a2a3b519de727b0f7903
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.