[syzbot ci] Re: netfilter: nf_tables: avoid chain re-validation if possible

[syzbot ci]

syzbot ci has tested the following series

[v3] netfilter: nf_tables: avoid chain re-validation if possible
https://lore.kernel.org/all/202512111230...@strlen.de
* [PATCH nf v3] netfilter: nf_tables: avoid chain re-validation if possible

and found the following issue:
WARNING in nft_chain_validate

Full report is available here:
https://ci.syzbot.org/series/498345c4-bb9b-4e13-9cd1-42a483844f55

***

WARNING in nft_chain_validate

tree: nf
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netfilter/nf.git
base: 6a107cfe9c99a079e578a4c5eb70038101a3599f
arch: amd64
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config: https://ci.syzbot.org/builds/e56f0271-a9ee-403c-ad73-fe3d0fb22785/config
C repro: https://ci.syzbot.org/findings/c4c03a63-b1c1-4815-b601-f7c763a99b6c/c_repro
syz repro: https://ci.syzbot.org/findings/c4c03a63-b1c1-4815-b601-f7c763a99b6c/syz_repro

------------[ cut here ]------------
WARNING: net/netfilter/nf_tables_api.c:4112 at nft_chain_vstate_update net/netfilter/nf_tables_api.c:4112 [inline], CPU#1: syz.0.17/5982
WARNING: net/netfilter/nf_tables_api.c:4112 at nft_chain_validate+0x6b0/0x8c0 net/netfilter/nf_tables_api.c:4176, CPU#1: syz.0.17/5982
Modules linked in:
CPU: 1 UID: 0 PID: 5982 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:nft_chain_vstate_update net/netfilter/nf_tables_api.c:4112 [inline]
RIP: 0010:nft_chain_validate+0x6b0/0x8c0 net/netfilter/nf_tables_api.c:4176
Code: 31 db 89 d8 48 83 c4 50 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 2d 32 42 f8 bb fc ff ff ff eb de e8 21 32 42 f8 90 <0f> 0b 90 49 83 c5 78 ba 04 00 00 00 4c 89 ef 31 f6 e8 ea 18 a8 f8
RSP: 0018:ffffc90003df6fe0 EFLAGS: 00010293
RAX: ffffffff897f183f RBX: 0000000000000000 RCX: ffff888102f93a80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000040 R08: ffff888102f93a80 R09: 0000000000000002
R10: 0000000000000010 R11: 0000000000000000 R12: ffff88816a79c510
R13: ffff88816a79c500 R14: ffff88816a79c500 R15: dffffc0000000000
FS: 000055555e417500(0000) GS:ffff8882a9eb1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000005000 CR3: 000000017531c000 CR4: 00000000000006f0
Call Trace:
<TASK>
nft_validate_register_store+0xf6/0x1d0 net/netfilter/nf_tables_api.c:11750
nft_parse_register_store+0x225/0x2c0 net/netfilter/nf_tables_api.c:11787
nft_immediate_init+0x1cf/0x390 net/netfilter/nft_immediate.c:67
nf_tables_newexpr net/netfilter/nf_tables_api.c:3550 [inline]
nf_tables_newrule+0x1794/0x28a0 net/netfilter/nf_tables_api.c:4419
nfnetlink_rcv_batch net/netfilter/nfnetlink.c:526 [inline]
nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:649 [inline]
nfnetlink_rcv+0x11d9/0x2590 net/netfilter/nfnetlink.c:667
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:718 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:733
____sys_sendmsg+0x505/0x820 net/socket.c:2608
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2662
__sys_sendmsg net/socket.c:2694 [inline]
__do_sys_sendmsg net/socket.c:2699 [inline]
__se_sys_sendmsg net/socket.c:2697 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2697
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f577a58f7c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe377887c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f577a7e5fa0 RCX: 00007f577a58f7c9
RDX: 0000000000000000 RSI: 00002000000000c0 RDI: 0000000000000003
RBP: 00007f577a5f297f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f577a7e5fa0 R14: 00007f577a7e5fa0 R15: 0000000000000003
</TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syz...@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzk...@googlegroups.com.

[Florian Westphal]

Righ, this patch depends on the already pending patch
"netfilter: nf_tables: remove redundant chain validation on register store",
which removes the only case where the function is called with ctx->chain
not set to a base chain.