cifs: avoid extra calls in posix_info_parse

In posix_info_parse() we call posix_info_sid_size twice for each of the owner and the group
sid. The first time to check that it is valid, i.e. >= 0 and the second time
to just pass it in as a length to memcpy().
As this is a pure function we know that it can not be negative the second time and this
is technically a false warning in coverity.
However, as it is a pure function we are just wasting cycles by calling it a second time.
Record the length from the first time we call it and save some cycles as well as make
Coverity happy.

Addresses-Coverity-ID: 1491379 ("Argument can not be negative")
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -4498,7 +4498,7 @@ int posix_info_parse(const void *beg, const void *end,
 
 {
 	int total_len = 0;
-	int sid_len;
+	int owner_len, group_len;
 	int name_len;
 	const void *owner_sid;
 	const void *group_sid;
@@ -4521,17 +4521,17 @@ int posix_info_parse(const void *beg, const void *end,
 
 	/* check owner sid */
 	owner_sid = beg + total_len;
-	sid_len = posix_info_sid_size(owner_sid, end);
-	if (sid_len < 0)
+	owner_len = posix_info_sid_size(owner_sid, end);
+	if (owner_len < 0)
 		return -1;
-	total_len += sid_len;
+	total_len += owner_len;
 
 	/* check group sid */
 	group_sid = beg + total_len;
-	sid_len = posix_info_sid_size(group_sid, end);
-	if (sid_len < 0)
+	group_len = posix_info_sid_size(group_sid, end);
+	if (group_len < 0)
 		return -1;
-	total_len += sid_len;
+	total_len += group_len;
 
 	/* check name len */
 	if (beg + total_len + 4 > end)
@@ -4552,10 +4552,8 @@ int posix_info_parse(const void *beg, const void *end,
 		out->size = total_len;
 		out->name_len = name_len;
 		out->name = name;
-		memcpy(&out->owner, owner_sid,
-		       posix_info_sid_size(owner_sid, end));
-		memcpy(&out->group, group_sid,
-		       posix_info_sid_size(group_sid, end));
+		memcpy(&out->owner, owner_sid, owner_len);
+		memcpy(&out->group, group_sid, group_len);
 	}
 	return total_len;
 }