WARNING in neigh_mark_dead

Status: upstream: reported on 2026/09/30 19:57
Subsystems: net
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+5a8857f0b4a0a7b12c62@syzkaller.appspotmail.com
First crash: 6d23h, last: 1d06h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
f7042c41 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING in neigh_mark_dead 2026/09/26 09:17 2026/09/26 09:17 2026/09/26 10:41 a3c7249d
719dc4b0 assessment-security 💥 WARNING in neigh_mark_dead 2026/09/25 00:34 2026/09/25 00:34 2026/09/25 01:47 3c3cdf19
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH v1 net-next 6/8] ipv6: Use ipv6_neigh_lookup() and friends. 1 (1) 2026/09/30 20:03
[syzbot] [net?] WARNING in neigh_mark_dead 0 (1) 2026/09/30 19:57

Sample crash report:
netlink: 'syz.0.857': attribute type 4 has an invalid length.
------------[ cut here ]------------
debug_locks && !(lock_is_held(&(&n->tbl->lock)->dep_map) != 0)
WARNING: net/core/neighbour.c:154 at neigh_mark_dead+0x2fb/0x340 net/core/neighbour.c:154, CPU#0: syz.0.857/9765
Modules linked in:
CPU: 0 UID: 0 PID: 9765 Comm: syz.0.857 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:neigh_mark_dead+0x2fb/0x340 net/core/neighbour.c:154
Code: e8 03 42 80 3c 28 00 74 08 48 89 df e8 ee 9a 80 f8 4c 89 33 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 86 95 10 f8 90 <0f> 0b 90 e9 8f fd ff ff 48 c7 c1 80 9a 7a 90 80 e1 07 80 c1 03 38
RSP: 0018:ffffc90003726600 EFLAGS: 00010287
RAX: ffffffff89b7467a RBX: ffff888022e86000 RCX: 0000000000080000
RDX: ffffc900047fa000 RSI: 0000000000003e08 RDI: 0000000000003e09
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520006e4cb8 R12: ffff888022e8613c
R13: dffffc0000000000 R14: ffff888022e86020 R15: ffff888022e86000
FS:  00007f9c30f046c0(0000) GS:ffff888124cc6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000076c56000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 neigh_flush_one+0x27c/0x5a0 net/core/neighbour.c:388
 neigh_flush_dev net/core/neighbour.c:432 [inline]
 __neigh_ifdown+0x1fb/0xc70 net/core/neighbour.c:465
 neigh_ifdown+0x1f/0x30 net/core/neighbour.c:487
 rt6_disable_ip+0x751/0x7e0 net/ipv6/route.c:5058
 addrconf_ifdown+0x155/0x1ad0 net/ipv6/addrconf.c:3892
 addrconf_notify+0x1bc/0x1050 net/ipv6/addrconf.c:-1
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 call_netdevice_notifiers_mtu net/core/dev.c:2350 [inline]
 netif_set_mtu_ext+0x5ac/0x830 net/core/dev.c:9963
 do_setlink+0xa81/0x47a0 net/core/rtnetlink.c:3247
 rtnl_setlink+0x578/0x820 net/core/rtnetlink.c:3623
 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7159
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2572
 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
 netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1361
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1916
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 sock_write_iter+0x2de/0x3e0 net/socket.c:1266
 do_iter_readv_writev+0x612/0x8c0 fs/read_write.c:-1
 vfs_writev+0x343/0x990 fs/read_write.c:1058
 do_writev+0x154/0x2e0 fs/read_write.c:1104
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9c2ff9e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9c30f04028 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f9c30225fa0 RCX: 00007f9c2ff9e159
RDX: 0000000000000001 RSI: 00002000000003c0 RDI: 0000000000000004
RBP: 00007f9c3003506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9c30226038 R14: 00007f9c30225fa0 R15: 00007ffed3c74808
 </TASK>

Crashes (11):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/28 01:27 net-next 014d795c7383 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in neigh_mark_dead
2026/09/29 16:54 linux-next 6375e61c01e9 7bf4ea23 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce WARNING in neigh_mark_dead
2026/09/28 22:59 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/28 22:58 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/28 22:57 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/28 22:55 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/28 22:55 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/28 20:59 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/26 13:33 linux-next f5f84daefcd9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce WARNING in neigh_mark_dead
2026/09/24 00:02 linux-next a8c591ed6b67 0a1606bc .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
2026/09/23 23:53 linux-next a8c591ed6b67 0a1606bc .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in neigh_mark_dead
* Struck through repros no longer work on HEAD.