cifs: always initialize struct msghdr smb_msg completely

So far we were just lucky because the uninitialized members
of struct msghdr are not used by default on a SOCK_STREAM tcp
socket.

But as new things like msg_ubuf and sg_from_iter where added
recently, we should play on the safe side and avoid potention
problems in future.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Cc: stable@vger.kernel.org
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -702,9 +702,6 @@ cifs_readv_from_socket(struct TCP_Server_Info *server, struct msghdr *smb_msg)
 	int length = 0;
 	int total_read;
 
-	smb_msg->msg_control = NULL;
-	smb_msg->msg_controllen = 0;
-
 	for (total_read = 0; msg_data_left(smb_msg); total_read += length) {
 		try_to_freeze();
 
@@ -760,7 +757,7 @@ int
 cifs_read_from_socket(struct TCP_Server_Info *server, char *buf,
 		      unsigned int to_read)
 {
-	struct msghdr smb_msg;
+	struct msghdr smb_msg = {};
 	struct kvec iov = {.iov_base = buf, .iov_len = to_read};
 	iov_iter_kvec(&smb_msg.msg_iter, READ, &iov, 1, to_read);
 
@@ -770,15 +767,13 @@ cifs_read_from_socket(struct TCP_Server_Info *server, char *buf,
 ssize_t
 cifs_discard_from_socket(struct TCP_Server_Info *server, size_t to_read)
 {
-	struct msghdr smb_msg;
+	struct msghdr smb_msg = {};
 
 	/*
 	 *  iov_iter_discard already sets smb_msg.type and count and iov_offset
 	 *  and cifs_readv_from_socket sets msg_control and msg_controllen
 	 *  so little to initialize in struct msghdr
 	 */
-	smb_msg.msg_name = NULL;
-	smb_msg.msg_namelen = 0;
 	iov_iter_discard(&smb_msg.msg_iter, READ, to_read);
 
 	return cifs_readv_from_socket(server, &smb_msg);
@@ -788,7 +783,7 @@ int
 cifs_read_page_from_socket(struct TCP_Server_Info *server, struct page *page,
 	unsigned int page_offset, unsigned int to_read)
 {
-	struct msghdr smb_msg;
+	struct msghdr smb_msg = {};
 	struct bio_vec bv = {
 		.bv_page = page, .bv_len = to_read, .bv_offset = page_offset};
 	iov_iter_bvec(&smb_msg.msg_iter, READ, &bv, 1, to_read);

fs/cifs/transport.c

@@ -194,10 +194,6 @@ smb_send_kvec(struct TCP_Server_Info *server, struct msghdr *smb_msg,
 
 	*sent = 0;
 
-	smb_msg->msg_name = NULL;
-	smb_msg->msg_namelen = 0;
-	smb_msg->msg_control = NULL;
-	smb_msg->msg_controllen = 0;
 	if (server->noblocksnd)
 		smb_msg->msg_flags = MSG_DONTWAIT + MSG_NOSIGNAL;
 	else
@@ -309,7 +305,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 	sigset_t mask, oldmask;
 	size_t total_len = 0, sent, size;
 	struct socket *ssocket = server->ssocket;
-	struct msghdr smb_msg;
+	struct msghdr smb_msg = {};
 	__be32 rfc1002_marker;
 
 	if (cifs_rdma_enabled(server)) {