samples/landlock: Fix incorrect free in populate_ruleset_net

Pointer env_port_name changes after strsep(). Memory allocated via
strdup() will not be freed if landlock_add_rule() returns non-zero value.

Fixes: 5e990dc ("samples/landlock: Support TCP restrictions")
Signed-off-by: Ivanov Mikhail <ivanov.mikhail1@huawei-partners.com>
Reviewed-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20240326095625.3576164-1-ivanov.mikhail1@huawei-partners.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Author: sm1ling-knight

samples/landlock/sandboxer.c

@@ -153,7 +153,7 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
 				const __u64 allowed_access)
 {
 	int ret = 1;
-	char *env_port_name, *strport;
+	char *env_port_name, *env_port_name_next, *strport;
 	struct landlock_net_port_attr net_port = {
 		.allowed_access = allowed_access,
 		.port = 0,
@@ -165,7 +165,8 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
 	env_port_name = strdup(env_port_name);
 	unsetenv(env_var);
 
-	while ((strport = strsep(&env_port_name, ENV_DELIMITER))) {
+	env_port_name_next = env_port_name;
+	while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) {
 		net_port.port = atoi(strport);
 		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
 				      &net_port, 0)) {