net: netlink: Check address length before reading groups field

mainline inclusion
from mainline-5.1-rc6
commit d852be84770c
category: bugfix
bugzilla: 14091
CVE: NA

-------------------------------------------------

KMSAN will complain if valid address length passed to bind() is shorter
than sizeof(struct sockaddr_nl) bytes.
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NZhiqiang Liu <liuzhiqiang26@huawei.com>
Reviewed-by: NWenan Mao <maowenan@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/netlink/af_netlink.c

@@ -993,7 +993,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 	struct netlink_sock *nlk = nlk_sk(sk);
 	struct sockaddr_nl *nladdr = (struct sockaddr_nl *)addr;
 	int err = 0;
-	unsigned long groups = nladdr->nl_groups;
+	unsigned long groups;
 	bool bound;
 
 	if (addr_len < sizeof(struct sockaddr_nl))
@@ -1001,6 +1001,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 
 	if (nladdr->nl_family != AF_NETLINK)
 		return -EINVAL;
+	groups = nladdr->nl_groups;
 
 	/* Only superuser is allowed to listen multicasts */
 	if (groups) {