tcp: add rcu protection around tp->fastopen_rsk

Both tcp_v4_err() and tcp_v6_err() do the following operations
while they do not own the socket lock :

	fastopen = tp->fastopen_rsk;
 	snd_una = fastopen ? tcp_rsk(fastopen)->snt_isn : tp->snd_una;

The problem is that without appropriate barrier, the compiler
might reload tp->fastopen_rsk and trigger a NULL deref.

request sockets are protected by RCU, we can simply add
the missing annotations and barriers to solve the issue.

Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index dbcf34ec8dd2..eb30fc1770de 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -906,7 +906,7 @@ static void inet_child_forget(struct sock *sk, struct request_sock *req,
         percpu_counter_inc(sk->sk_prot->orphan_count);
 
         if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(req)->tfo_listener) {
-                BUG_ON(tcp_sk(child)->fastopen_rsk != req);
+                BUG_ON(rcu_access_pointer(tcp_sk(child)->fastopen_rsk) != req);
                 BUG_ON(sk != req->rsk_listener);
 
                 /* Paranoid, to prevent race condition if
@@ -915,7 +915,7 @@ static void inet_child_forget(struct sock *sk, struct request_sock *req,
                  * Also to satisfy an assertion in
                  * tcp_v4_destroy_sock().
                  */
-                tcp_sk(child)->fastopen_rsk = NULL;
+                RCU_INIT_POINTER(tcp_sk(child)->fastopen_rsk, NULL);
         }
         inet_csk_destroy_sock(child);
 }