From: Tijs Van Buggenhout tijs.van.buggenhout@axsguard.com
[ Upstream commit e1f543dc660b44618a1bd72ddb4ca0828a95f7ad ]
An nf_conntrack_helper from nf_conn_help may become NULL after DNAT.
Observed when TCP port 1720 (Q931_PORT), associated with h323 conntrack helper, is DNAT'ed to another destination port (e.g. 1730), while nfqueue is being used for final acceptance (e.g. snort).
This happenned after transition from kernel 4.14 to 5.10.161.
Workarounds: * keep the same port (1720) in DNAT * disable nfqueue * disable/unload h323 NAT helper
$ linux-5.10/scripts/decode_stacktrace.sh vmlinux < /tmp/kernel.log BUG: kernel NULL pointer dereference, address: 0000000000000084 [..] RIP: 0010:nf_conntrack_update (net/netfilter/nf_conntrack_core.c:2080 net/netfilter/nf_conntrack_core.c:2134) nf_conntrack [..] nfqnl_reinject (net/netfilter/nfnetlink_queue.c:237) nfnetlink_queue nfqnl_recv_verdict (net/netfilter/nfnetlink_queue.c:1230) nfnetlink_queue nfnetlink_rcv_msg (net/netfilter/nfnetlink.c:241) nfnetlink [..]
Fixes: ee04805ff54a ("netfilter: conntrack: make conntrack userspace helpers work again") Signed-off-by: Tijs Van Buggenhout tijs.van.buggenhout@axsguard.com Signed-off-by: Florian Westphal fw@strlen.de Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/netfilter/nf_conntrack_core.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 193a18bfddc0a..f82a234ac53a1 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -2075,6 +2075,9 @@ static int nf_confirm_cthelper(struct sk_buff *skb, struct nf_conn *ct, return 0;
helper = rcu_dereference(help->helper); + if (!helper) + return 0; + if (!(helper->flags & NF_CT_HELPER_F_USERSPACE)) return 0;