CIFS: Clarify SMB1 code for SetFileSize

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 setting the file size using SMB1. This changeset
doesn't change the address but makes it slightly clearer.

Addresses-Coverity: 711525 ("Out of bounds write")
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: smfrench

fs/cifs/cifssmb.c

@@ -5628,9 +5628,9 @@ CIFSSMBSetFileSize(const unsigned int xid, struct cifs_tcon *tcon,
 	pSMB->TotalDataCount = pSMB->DataCount;
 	pSMB->TotalParameterCount = pSMB->ParameterCount;
 	pSMB->ParameterOffset = cpu_to_le16(param_offset);
+	/* SMB offsets are from the beginning of SMB which is 4 bytes in, after RFC1001 field */
 	parm_data =
-		(struct file_end_of_file_info *) (((char *) &pSMB->hdr.Protocol)
-				+ offset);
+		(struct file_end_of_file_info *)(((char *)pSMB) + offset + 4);
 	pSMB->DataOffset = cpu_to_le16(offset);
 	parm_data->FileSize = cpu_to_le64(size);
 	pSMB->Fid = cfile->fid.netfid;