[syzbot] [netfilter?] WARNING in nf_reject_fill_skb_dst

[syzbot <syzbot+b17c05ecb64771a892d1@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    5c69e0b395c1 Merge branch 'stmmac-stop-silently-dropping-b..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=128597a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5b2fdcd062d798f6
dashboard link: https://syzkaller.appspot.com/bug?extid=b17c05ecb64771a892d1
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=12175442580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=124c16f0580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ef95b68de898/disk-5c69e0b3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/70d343b8a3cf/vmlinux-5c69e0b3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/55dad8818bb6/bzImage-5c69e0b3.xz

The issue was bisected to:

commit a890348adcc993f48d1ae38f1174dc8de4c3c5ac
Author: Stanislav Fomichev <sdf@fomichev.me>
Date:   Mon Aug 18 15:40:32 2025 +0000

    net: Add skb_dst_check_unset

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12d1b7a2580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=11d1b7a2580000
console output: https://syzkaller.appspot.com/x/log.txt?x=16d1b7a2580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b17c05ecb64771a892d1@syzkaller.appspotmail.com
Fixes: a890348adcc9 ("net: Add skb_dst_check_unset")

------------[ cut here ]------------
WARNING: CPU: 1 PID: 1038 at ./include/linux/skbuff.h:1165 skb_dst_check_unset include/linux/skbuff.h:1164 [inline]
WARNING: CPU: 1 PID: 1038 at ./include/linux/skbuff.h:1165 skb_dst_set include/linux/skbuff.h:1211 [inline]
WARNING: CPU: 1 PID: 1038 at ./include/linux/skbuff.h:1165 nf_reject_fill_skb_dst+0x2a4/0x330 net/ipv4/netfilter/nf_reject_ipv4.c:234
Modules linked in:
CPU: 1 UID: 0 PID: 1038 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: ipv6_addrconf addrconf_dad_work
RIP: 0010:skb_dst_check_unset include/linux/skbuff.h:1164 [inline]
RIP: 0010:skb_dst_set include/linux/skbuff.h:1211 [inline]
RIP: 0010:nf_reject_fill_skb_dst+0x2a4/0x330 net/ipv4/netfilter/nf_reject_ipv4.c:234
Code: 8b 0d 10 6f 8b 08 48 3b 8c 24 e0 00 00 00 75 5d 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 fd ca aa f7 90 <0f> 0b 90 e9 38 ff ff ff 44 89 f9 80 e1 07 fe c1 38 c1 0f 8c 2b fe
RSP: 0018:ffffc90000a08360 EFLAGS: 00010246
RAX: ffffffff8a14e133 RBX: ffff888079c898c0 RCX: ffff8880266ada00
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000a08490 R08: ffffffff8fa37e37 R09: 1ffffffff1f46fc6
R10: dffffc0000000000 R11: fffffbfff1f46fc7 R12: ffff88807be46101
R13: dffffc0000000001 R14: 1ffff92000141070 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888125d1b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f95283b6088 CR3: 000000000df36000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 nf_send_unreach+0x17b/0x6e0 net/ipv4/netfilter/nf_reject_ipv4.c:325
 nft_reject_inet_eval+0x4bc/0x690 net/netfilter/nft_reject_inet.c:27
 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
 nft_do_chain+0x40c/0x1920 net/netfilter/nf_tables_core.c:285
 nft_do_chain_inet+0x25d/0x340 net/netfilter/nft_chain_filter.c:161
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:623
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x206/0x3a0 include/linux/netfilter.h:316
 __netif_receive_skb_one_core net/core/dev.c:5979 [inline]
 __netif_receive_skb+0x143/0x380 net/core/dev.c:6092
 process_backlog+0x60e/0x14f0 net/core/dev.c:6444
 __napi_poll+0xc7/0x360 net/core/dev.c:7494
 napi_poll net/core/dev.c:7557 [inline]
 net_rx_action+0x707/0xe30 net/core/dev.c:7684
 handle_softirqs+0x283/0x870 kernel/softirq.c:579
 do_softirq+0xec/0x180 kernel/softirq.c:480
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x17d/0x1c0 kernel/softirq.c:407
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:910 [inline]
 __dev_queue_xmit+0x1d79/0x3b50 net/core/dev.c:4740
 neigh_output include/net/neighbour.h:547 [inline]
 ip6_finish_output2+0x11fb/0x16a0 net/ipv6/ip6_output.c:141
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ndisc_send_skb+0xb96/0x1470 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:3236 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x711/0x8a0 kernel/kthread.c:463


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup