From: Naman Gulati <namangulati@google.com>
To: Pablo Neira Ayuso <pablo@netfilter.org>,
Florian Westphal <fw@strlen.de>,
"David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>
Cc: Phil Sutter <phil@nwl.cc>, Simon Horman <horms@kernel.org>,
netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
netdev@vger.kernel.org,
syzbot+4bd730aede2791e40bdf@syzkaller.appspotmail.com,
Naman Gulati <namangulati@google.com>
Subject: [PATCH net] netfilter: ctnetlink: fix suspicious RCU usage in expect_iter_name
Date: Sat, 12 Sep 2026 01:10:51 +0000 [thread overview]
Message-ID: <20260912011051.4092897-1-namangulati@google.com> (raw)
expect_iter_name() is invoked by nf_ct_expect_iterate_net() under
spin_lock_bh(&nf_conntrack_expect_lock). It does not hold
rcu_read_lock().
When accessing exp->helper with rcu_dereference() in syzbot's report,
lockdep warns:
=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
net/netfilter/nf_conntrack_netlink.c:3393 suspicious rcu_dereference_check() usage!
locks held by syz-executor381/5628: 2, last CPU#1:
#0: ffffffff9aee42a0 (nfnl_subsys_ctnetlink_exp){+.+.}-{4:4},
at: nfnetlink_rcv_msg+0xa69/0x12b0
#1: ffffffff8ea74d58 (nf_conntrack_expect_lock){+...}-{3:3},
at: nf_ct_expect_iterate_net+0x38/0x180
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150
lockdep_rcu_suspicious+0x140/0x1d0
expect_iter_name+0xfb/0x100
nf_ct_expect_iterate_net+0xf2/0x180
ctnetlink_del_expect+0x45d/0x640
nfnetlink_rcv_msg+0xcc2/0x12b0
netlink_rcv_skb+0x226/0x4a0
nfnetlink_rcv+0x2b9/0x28c0
netlink_unicast+0x7bd/0x940
netlink_sendmsg+0x813/0xb40
____sys_sendmsg+0x54e/0x850
___sys_sendmsg+0x2a5/0x360
__sys_sendmsg+0x2a5/0x360
do_syscall_64+0x166/0x520
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Use rcu_dereference_protected() with lockdep_is_held() on
nf_conntrack_expect_lock instead, similar to expect_iter_me() in
nf_conntrack_helper.c.
Fixes: f01794106042 ("netfilter: nf_conntrack_expect: use expect->helper")
Reported-by: syzbot+4bd730aede2791e40bdf@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6aa4a377.f81106d8.2ab401.0024.GAE@google.com/T/#u
Signed-off-by: Naman Gulati <namangulati@google.com>
---
net/netfilter/nf_conntrack_netlink.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 579ada063b1b..4e5d7c701436 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3392,7 +3392,8 @@ static bool expect_iter_name(struct nf_conntrack_expect *exp, void *data)
struct nf_conntrack_helper *helper;
const char *name = data;
- helper = rcu_dereference(exp->helper);
+ helper = rcu_dereference_protected(exp->helper,
+ lockdep_is_held(&nf_conntrack_expect_lock));
if (!helper)
return false;
--
2.55.0.1007.g17ff1f9808-goog
reply other threads:[~2026-09-12 1:11 UTC|newest]
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