bpf: Check address length before reading address family

KMSAN will complain if valid address length passed to bpf_bind() is
shorter than sizeof("struct sockaddr"->sa_family) bytes.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -4383,6 +4383,8 @@ BPF_CALL_3(bpf_bind, struct bpf_sock_addr_kern *, ctx, struct sockaddr *, addr,
 	 * Only binding to IP is supported.
 	 */
 	err = -EINVAL;
+	if (addr_len < offsetofend(struct sockaddr, sa_family))
+		return err;
 	if (addr->sa_family == AF_INET) {
 		if (addr_len < sizeof(struct sockaddr_in))
 			return err;