kconfig: use snprintf for formatting pathnames

Valid pathnames will never exceed PATH_MAX, but these file names
are unsanitized and can cause buffer overflow if set incorrectly.
Use snprintf to avoid this. This was flagged during a Coverity scan
of the coreboot project, which also uses kconfig for its build system.
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/confdata.c

@@ -241,7 +241,7 @@ char *conf_get_default_confname(void)
 	name = expand_string(conf_defname);
 	env = getenv(SRCTREE);
 	if (env) {
-		sprintf(fullname, "%s/%s", env, name);
+		snprintf(fullname, sizeof(fullname), "%s/%s", env, name);
 		if (is_present(fullname))
 			return fullname;
 	}

scripts/kconfig/lexer.l

@@ -378,7 +378,8 @@ FILE *zconf_fopen(const char *name)
 	if (!f && name != NULL && name[0] != '/') {
 		env = getenv(SRCTREE);
 		if (env) {
-			sprintf(fullname, "%s/%s", env, name);
+			snprintf(fullname, sizeof(fullname),
+				 "%s/%s", env, name);
 			f = fopen(fullname, "r");
 		}
 	}