diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 7de69e161c34..a3a2b6df2ee2 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3847,13 +3847,13 @@ EXPORT_SYMBOL(tcp_md5_hash_skb_data);
 
 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp, const struct tcp_md5sig_key *key)
 {
-	u8 keylen = key->keylen;
+	u8 keylen = READ_ONCE(key->keylen); /* paired with WRITE_ONCE() in tcp_md5_do_add */
 	struct scatterlist sg;
 
-	smp_rmb(); /* paired with smp_wmb() in tcp_md5_do_add() */
-
 	sg_init_one(&sg, key->key, keylen);
 	ahash_request_set_crypt(hp->md5_req, &sg, NULL, keylen);
+
+	/* tcp_md5_do_add() might change key->key under us */
 	return crypto_ahash_update(hp->md5_req);
 }
 EXPORT_SYMBOL(tcp_md5_hash_key);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 7bb8747d86f1..35f963690a70 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1077,12 +1077,18 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
 
 	key = tcp_md5_do_lookup_exact(sk, addr, family, prefixlen);
 	if (key) {
-		/* Pre-existing entry - just update that one. */
+		/* Pre-existing entry - just update that one.
+		 * Note that the key might be used concurrently.
+		 */
 		memcpy(key->key, newkey, newkeylen);
 
-		smp_wmb(); /* pairs with smp_rmb() in tcp_md5_hash_key() */
+		/* Pairs with READ_ONCE() in tcp_md5_hash_key().
+		 * Also note that a reader could catch new key->keylen value
+		 * but old key->key[], this is the reason we use __GFP_ZERO
+		 * at sock_kmalloc() time below these lines.
+		 */
+		WRITE_ONCE(key->keylen, newkeylen);
 
-		key->keylen = newkeylen;
 		return 0;
 	}
 
@@ -1098,7 +1104,7 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
 		rcu_assign_pointer(tp->md5sig_info, md5sig);
 	}
 
-	key = sock_kmalloc(sk, sizeof(*key), gfp);
+	key = sock_kmalloc(sk, sizeof(*key), gfp | __GFP_ZERO);
 	if (!key)
 		return -ENOMEM;
 	if (!tcp_alloc_md5sig_pool()) {