[syzbot] [netfilter?] WARNING in xt_dnat_target_v2

[syzbot] [netfilter?] WARNING in xt_dnat_target_v2

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    787268686c64 ipmr, ip6mr: queue netlink route queries out ..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git
console output: https://syzkaller.appspot.com/x/log.txt?x=170b444e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d30e1495ee3ac817
dashboard link: https://syzkaller.appspot.com/bug?extid=2e819f6641708bb6ab9d
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=108b444e580000

AI-generated root cause summary:
When an incoming TCP packet is rejected by an nftables reject rule
(nft_reject_ipv4_eval), nf_send_reset() creates a TCP RST reply and attaches the
original packet's conntrack entry via nf_ct_attach(), marking its ctinfo as
IP_CT_RELATED_REPLY. As the RST packet traverses the NF_INET_LOCAL_OUT hook,
nf_nat_ipv4_fn() passes it to nf_nat_inet_fn() because it is not an ICMP packet.
In nf_nat_inet_fn(), IP_CT_RELATED_REPLY falls through to evaluation of
uninitialized NAT mappings, executing rules in the LOCAL_OUT NAT chain. If the
chain includes an xtables DNAT target (evaluated via nft_compat),
xt_dnat_target_v2() triggers WARN_ON because its assertion checks only for
IP_CT_NEW or IP_CT_RELATED, omitting IP_CT_RELATED_REPLY.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=2e819f6641708bb6ab9d

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2e819f6641708bb6ab9d@syzkaller.appspotmail.com

------------[ cut here ]------------
!(ct != NULL && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED))
WARNING: net/netfilter/xt_nat.c:154 at xt_dnat_target_v2+0x97/0xc0 net/netfilter/xt_nat.c:153, CPU#0: syz-executor145/6031
Modules linked in:
CPU: 0 UID: 0 PID: 6031 Comm: syz-executor145 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026
RIP: 0010:xt_dnat_target_v2+0x97/0xc0 net/netfilter/xt_nat.c:153
Code: 74 22 41 83 e7 07 41 83 c7 fd bf fe ff ff ff 44 89 fe e8 ac 1e 90 f7 41 83 ff fe 72 25 e8 91 19 90 f7 eb 09 e8 8a 19 90 f7 90 <0f> 0b 90 4c 89 f7 48 89 de ba 01 00 00 00 5b 41 5e 41 5f e9 21 17
RSP: 0018:ffffc90000006de0 EFLAGS: 00010246
RAX: ffffffff8a38fc64 RBX: ffff8880614cd418 RCX: ffff88807c979f40
RDX: 0000000000000100 RSI: 0000000000000100 RDI: 00000000fffffffe
RBP: ffffc90000006ed0 R08: 0000000000000100 R09: 0000000000000000
R10: ffffc900000070b0 R11: ffffffff8a38fbb0 R12: ffffffff919e5438
R13: 1ffff92000000dc4 R14: ffff8880247c8900 R15: 0000000000000001
FS:  0000555563505400(0000) GS:ffff88812361d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe16ab8280 CR3: 0000000034dea000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 nft_target_eval_xt+0x1ad/0x2b0 net/netfilter/nft_compat.c:100
 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
 nft_do_chain+0x48d/0x1b10 net/netfilter/nf_tables_core.c:285
 nft_nat_do_chain+0x360/0x4b0 net/netfilter/nft_chain_nat.c:32
 nf_nat_inet_fn+0x5de/0xb50 net/netfilter/nf_nat_core.c:931
 nf_nat_ipv4_fn net/netfilter/nf_nat_proto.c:583 [inline]
 nf_nat_ipv4_local_fn+0x18c/0x570 net/netfilter/nf_nat_proto.c:738
 nf_hook_entry_hookfn include/linux/netfilter.h:165 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:633
 nf_hook+0x22a/0x3a0 include/linux/netfilter.h:280
 __ip_local_out+0x558/0x6a0 net/ipv4/ip_output.c:120
 ip_local_out+0x2a/0x190 net/ipv4/ip_output.c:129
 nf_send_reset+0xd8d/0x1530 net/ipv4/netfilter/nf_reject_ipv4.c:339
 nft_reject_ipv4_eval+0xf6/0x230 net/ipv4/netfilter/nft_reject_ipv4.c:30
 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
 nft_do_chain+0x48d/0x1b10 net/netfilter/nf_tables_core.c:285
 nft_do_chain_ipv4+0x195/0x290 net/netfilter/nft_chain_filter.c:24
 nf_hook_entry_hookfn include/linux/netfilter.h:165 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:633
 nf_hook include/linux/netfilter.h:280 [inline]
 NF_HOOK+0x21f/0x3c0 include/linux/netfilter.h:323
 __netif_receive_skb_one_core net/core/dev.c:6433 [inline]
 __netif_receive_skb net/core/dev.c:6546 [inline]
 process_backlog+0xa6b/0x18b0 net/core/dev.c:6897
 __napi_poll+0xaa/0x330 net/core/dev.c:7977
 napi_poll net/core/dev.c:8040 [inline]
 net_rx_action+0x61d/0xf50 net/core/dev.c:8197
 handle_softirqs+0x265/0x8d0 kernel/softirq.c:669
 do_softirq+0x77/0xd0 kernel/softirq.c:569
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x100/0x140 kernel/softirq.c:473
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:923 [inline]
 __dev_queue_xmit+0x1efb/0x3920 net/core/dev.c:5121
 neigh_output include/net/neighbour.h:554 [inline]
 ip_finish_output2+0xc4b/0x10b0 net/ipv4/ip_output.c:236
 NF_HOOK_COND include/linux/netfilter.h:314 [inline]
 ip_output+0x29f/0x450 net/ipv4/ip_output.c:437
 __ip_queue_xmit+0x10df/0x1b10 net/ipv4/ip_output.c:533
 __tcp_transmit_skb+0x2d06/0x47b0 net/ipv4/tcp_output.c:1773
 tcp_transmit_skb net/ipv4/tcp_output.c:1790 [inline]
 tcp_connect+0x1a7e/0x4990 net/ipv4/tcp_output.c:4451
 tcp_v4_connect+0x1264/0x1b20 net/ipv4/tcp_ipv4.c:348
 __inet_stream_connect+0x28c/0xf50 net/ipv4/af_inet.c:684
 inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:755
 connect_socket net/socket.c:2143 [inline]
 __sys_connect_file net/socket.c:2168 [inline]
 __sys_connect+0x316/0x450 net/socket.c:2185
 __do_sys_connect net/socket.c:2191 [inline]
 __se_sys_connect net/socket.c:2188 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2188
 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: 0033:0x7f81c24b2ff7
Code: 48 89 fa 4c 89 df e8 98 1d 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffe16aca280 EFLAGS: 00000202 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000555563505400 RCX: 00007f81c24b2ff7
RDX: 0000000000000010 RSI: 00007ffe16aca300 RDI: 0000000000000005
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000d2040002
R13: 00007f81c24eed50 R14: 00007ffe16aca300 R15: 00007f81c24ec06c
 </TASK>


---
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Forwarded: Re: [syzbot] [netfilter?] WARNING in xt_dnat_target_v2

[syzbot]

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Subject: Re: [syzbot] [netfilter?] WARNING in xt_dnat_target_v2
Author: xujiahao@cmss.chinamobile.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git master

Testing the attached patch for this crash.

Forwarded: Re: [syzbot] [netfilter?] WARNING in xt_dnat_target_v2

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

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Subject: Re: [syzbot] [netfilter?] WARNING in xt_dnat_target_v2
Author: xujiahao@cmss.chinamobile.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Testing the attached patch for this crash.