cifs: clarify SMB1 code for UnixCreateHardLink

Coverity 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).  This doesn't change the address but
makes it slightly clearer.

Addresses-Coverity: 711529 ("Out of bounds read")
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifspdu.h

@@ -1785,6 +1785,7 @@ struct smb_com_transaction2_sfi_req {
 	__u16 Fid;
 	__le16 InformationLevel;
 	__u16 Reserved4;
+	__u8  payload[];
 } __attribute__((packed));
 
 struct smb_com_transaction2_sfi_rsp {

fs/cifs/cifssmb.c

@@ -3009,7 +3009,8 @@ CIFSUnixCreateHardLink(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, fromName,