net/rds: Check address length before reading address family

syzbot is reporting uninitialized value at rds_connect() [1] and
rds_bind() [2]. This is because syzbot is passing ulen == 0 whereas
these functions expect that it is safe to access sockaddr->family field
in order to determine minimal address length for validation.

[1] https://syzkaller.appspot.com/bug?id=f4e61c010416c1e6f0fa3ffe247561b60a50ad71
[2] https://syzkaller.appspot.com/bug?id=a4bf9e41b7e055c3823fdcd83e8c58ca7270e38fReported-by: syzbot <syzbot+0049bebbf3042dbd2e8f@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+915c9f99f3dbc4bd6cd1@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/af_rds.c

@@ -543,6 +543,9 @@ static int rds_connect(struct socket *sock, struct sockaddr *uaddr,
 	struct rds_sock *rs = rds_sk_to_rs(sk);
 	int ret = 0;
 
+	if (addr_len < offsetofend(struct sockaddr, sa_family))
+		return -EINVAL;
+
 	lock_sock(sk);
 
 	switch (uaddr->sa_family) {

net/rds/bind.c

@@ -173,6 +173,8 @@ int rds_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	/* We allow an RDS socket to be bound to either IPv4 or IPv6
 	 * address.
 	 */
+	if (addr_len < offsetofend(struct sockaddr, sa_family))
+		return -EINVAL;
 	if (uaddr->sa_family == AF_INET) {
 		struct sockaddr_in *sin = (struct sockaddr_in *)uaddr;