cifs: fix dereference on ses before it is null checked

The assignment of pointer server dereferences pointer ses, however,
this dereference occurs before ses is null checked and hence we
have a potential null pointer dereference.  Fix this by only
dereferencing ses after it has been null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: 2808c6639104 ("cifs: add new debugging macro cifs_server_dbg")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -2759,8 +2759,10 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	else
 		return -EIO;
 
+	if (!ses)
+		return -EIO;
 	server = ses->server;
-	if (!ses || !(server))
+	if (!server)
 		return -EIO;
 
 	if (smb3_encryption_required(tcon))
@@ -3058,13 +3060,16 @@ query_info(const unsigned int xid, struct cifs_tcon *tcon,
 	int rc = 0;
 	int resp_buftype = CIFS_NO_BUFFER;
 	struct cifs_ses *ses = tcon->ses;
-	struct TCP_Server_Info *server = ses->server;
+	struct TCP_Server_Info *server;
 	int flags = 0;
 	bool allocated = false;
 
 	cifs_dbg(FYI, "Query Info\n");
 
-	if (!ses || !(server))
+	if (!ses)
+		return -EIO;
+	server = ses->server;
+	if (!server)
 		return -EIO;
 
 	if (smb3_encryption_required(tcon))

fs/cifs/transport.c

@@ -1242,12 +1242,13 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
 	struct kvec iov = { .iov_base = in_buf, .iov_len = len };
 	struct smb_rqst rqst = { .rq_iov = &iov, .rq_nvec = 1 };
 	struct cifs_credits credits = { .value = 1, .instance = 0 };
-	struct TCP_Server_Info *server = ses->server;
+	struct TCP_Server_Info *server;
 
 	if (ses == NULL) {
 		cifs_dbg(VFS, "Null smb session\n");
 		return -EIO;
 	}
+	server = ses->server;
 	if (server == NULL) {
 		cifs_dbg(VFS, "Null tcp session\n");
 		return -EIO;