smb: server: Fix extension string in ksmbd_extract_shortname()

In ksmbd_extract_shortname(), strscpy() is incorrectly called with the
length of the source string (excluding the NUL terminator) rather than
the size of the destination buffer. This results in "__" being copied
to 'extension' rather than "___" (two underscores instead of three).

Use the destination buffer size instead to ensure that the string "___"
(three underscores) is copied correctly.

Cc: [email protected]
Fixes: e2f3448 ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Thorsten Blum <[email protected]>
Acked-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: toblux

fs/smb/server/smb_common.c

@@ -515,7 +515,7 @@ int ksmbd_extract_shortname(struct ksmbd_conn *conn, const char *longname,
 
 	p = strrchr(longname, '.');
 	if (p == longname) { /*name starts with a dot*/
-		strscpy(extension, "___", strlen("___"));
+		strscpy(extension, "___", sizeof(extension));
 	} else {
 		if (p) {
 			p++;