smb3: add additional null check in SMB2_ioctl

Although unlikely for it to be possible for rsp to be null here,
the check is safer to add, and quiets a Coverity warning.

Addresses-Coverity: 1443909 ("Explicit Null dereference")
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: smfrench

fs/cifs/smb2pdu.c

@@ -3162,6 +3162,16 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	if ((plen == NULL) || (out_data == NULL))
 		goto ioctl_exit;
 
+	/*
+	 * Although unlikely to be possible for rsp to be null and rc not set,
+	 * adding check below is slightly safer long term (and quiets Coverity
+	 * warning)
+	 */
+	if (rsp == NULL) {
+		rc = -EIO;
+		goto ioctl_exit;
+	}
+
 	*plen = le32_to_cpu(rsp->OutputCount);
 
 	/* We check for obvious errors in the output buffer length and offset */