FAILED: patch "[PATCH] net: rds: acquire refcount on TCP sockets" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-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 3a58f13a881ed351198ffab4cf9953cf19d2ab3a Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <[email protected]>
Date: Mon, 2 May 2022 10:40:18 +0900
Subject: [PATCH] net: rds: acquire refcount on TCP sockets

syzbot is reporting use-after-free read in tcp_retransmit_timer() [1], for TCP socket used by RDS is accessing sock_net() without acquiring a refcount on net namespace. Since TCP's retransmission can happen after a process which created net namespace terminated, we need to explicitly acquire a refcount.

index 5327d130c4b5..2f638f8b7b1e 100644
@@ -495,6 +495,14 @@ void rds_tcp_tune(struct socket *sock)
 
 	tcp_sock_set_nodelay(sock->sk);
 	lock_sock(sk);
+	/* TCP timer functions might access net namespace even after
+	 * a process which created this net namespace terminated.
+	 */
+	if (!sk->sk_net_refcnt) {
+		sk->sk_net_refcnt = 1;
+		get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
+		sock_inuse_add(net, 1);
+	}
 	if (rtn->sndbuf_size > 0) {
 		sk->sk_sndbuf = rtn->sndbuf_size;
 		sk->sk_userlocks |= SOCK_SNDBUF_LOCK;