CIFS: Clarify SMB1 code for UnixCreateSymLink

Coverity also complains about the way we calculate the offset
(starting from the address of a 4 byte array within the
header structure rather than from the beginning of the struct
plus 4 bytes) for creating SMB1 symlinks when using the Unix
extensions.  This doesn't change the address but
makes it slightly clearer.

Addresses-Coverity: 711530 ("Out of bounds read")
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: smfrench

fs/cifs/cifssmb.c

@@ -2925,7 +2925,8 @@ CIFSUnixCreateSymLink(const unsigned int xid, struct cifs_tcon *tcon,
 				InformationLevel) - 4;
 	offset = param_offset + params;
 
-	data_offset = (char *) (&pSMB->hdr.Protocol) + offset;
+	/* SMB offsets are from the beginning of SMB which is 4 bytes in, after RFC1001 field */
+	data_offset = (char *)pSMB + offset + 4;
 	if (pSMB->hdr.Flags2 & SMBFLG2_UNICODE) {
 		name_len_target =
 		    cifsConvertToUTF16((__le16 *) data_offset, toName,