FAILED: patch "[PATCH] tcp: add a missing nf_reset_ct() in 3WHS handling" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6f0012e35160cd08a53e46e3b3bbf724b92dfe68 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <[email protected]>
Date: Thu, 23 Jun 2022 05:04:36 +0000
Subject: [PATCH] tcp: add a missing nf_reset_ct() in 3WHS handling

When the third packet of 3WHS connection establishment contains payload, it is added into socket receive queue without the XFRM check and the drop of connection tracking context.

This means that if the data is left unread in the socket receive queue, conntrack module can not be unloaded.

As most applications usually reads the incoming data immediately after accept(), bug has been hiding for quite a long time.

Commit 68822bdf76f1 ("net: generalize skb freeing deferral to per-cpu lists") exposed this bug because even if the application reads this data, the skb with nfct state could stay in a per-cpu cache for an arbitrary time, if said cpu no longer process RX softirqs.

Many thanks to Ilya Maximets for reporting this issue, and for testing various patches:
https://lore.kernel.org/netdev/[email protected]/

Note that I also added a missing xfrm4_policy_check() call, although this is probably not a big issue, as the SYN packet should have been dropped earlier.

index fe8f23b95d32..da5a3c44c4fb 100644
@@ -1964,7 +1964,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
 		struct sock *nsk;
 
 		sk = req->rsk_listener;
-		drop_reason = tcp_inbound_md5_hash(sk, skb,
+		if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
+			drop_reason = SKB_DROP_REASON_XFRM_POLICY;
+		else
+			drop_reason = tcp_inbound_md5_hash(sk, skb,
 						   &iph->saddr, &iph->daddr,
 						   AF_INET, dif, sdif);
 		if (unlikely(drop_reason)) {

@@ -2016,6 +2019,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 			}
 			goto discard_and_relse;
 		}
+		nf_reset_ct(skb);
 		if (nsk == sk) {
 			reqsk_put(req);
 			tcp_v4_restore_cb(skb);