confile: add lxc.init.groups to keep additional groups

src/lxc/conf.c

@@ -3919,6 +3919,7 @@ void lxc_conf_free(struct lxc_conf *conf)
 	free(conf->rcfile);
 	free(conf->execute_cmd);
 	free(conf->init_cmd);
+	free(conf->init_groups.list);
 	free(conf->init_cwd);
 	free(conf->unexpanded_config);
 	free(conf->syslog);

src/lxc/conf.h

@@ -417,6 +417,10 @@ struct lxc_conf {
 	 * should run under when using lxc-execute */
 	uid_t init_uid;
 	gid_t init_gid;
+	struct {
+		int size;
+		gid_t *list;
+	} init_groups;
 
 	/* indicator if the container will be destroyed on shutdown */
 	unsigned int ephemeral;

src/lxc/confile.c

@@ -94,6 +94,7 @@ lxc_config_define(init_cmd);
 lxc_config_define(init_cwd);
 lxc_config_define(init_gid);
 lxc_config_define(init_uid);
+lxc_config_define(init_groups);
 lxc_config_define(keyring_session);
 lxc_config_define(log_file);
 lxc_config_define(log_level);
@@ -211,6 +212,7 @@ static struct lxc_config_t config_jump_table[] = {
 	{ "lxc.include",                    set_config_includefiles,               get_config_includefiles,               clr_config_includefiles,               },
 	{ "lxc.init.cmd",                   set_config_init_cmd,                   get_config_init_cmd,                   clr_config_init_cmd,                   },
 	{ "lxc.init.gid",                   set_config_init_gid,                   get_config_init_gid,                   clr_config_init_gid,                   },
+	{ "lxc.init.groups",                set_config_init_groups,                get_config_init_groups,                clr_config_init_groups,                },
 	{ "lxc.init.uid",                   set_config_init_uid,                   get_config_init_uid,                   clr_config_init_uid,                   },
 	{ "lxc.init.cwd",                   set_config_init_cwd,                   get_config_init_cwd,                   clr_config_init_cwd,                   },
 	{ "lxc.keyring.session",            set_config_keyring_session,            get_config_keyring_session,            clr_config_keyring_session             },
@@ -1178,6 +1180,53 @@ static int set_config_init_gid(const char *key, const char *value,
 	return 0;
 }
 
+static int set_config_init_groups(const char *key, const char *value,
+				  struct lxc_conf *lxc_conf, void *data)
+{
+	__do_free char *value_dup = NULL;
+	__do_free gid_t *init_groups = NULL;
+	int num_groups = 0;
+	int iter = 0;
+	char *token;
+
+	if (lxc_config_value_empty(value))
+		return clr_config_init_groups(key, lxc_conf, NULL);
+
+	value_dup = strdup(value);
+	if (!value_dup)
+		return -ENOMEM;
+
+	lxc_iterate_parts(token, value_dup, ",")
+		num_groups++;
+
+	if (num_groups == 0)
+		return clr_config_init_groups(key, lxc_conf, NULL);
+
+	init_groups = zalloc(sizeof(gid_t) * num_groups);
+	if (!init_groups)
+		return ret_errno(ENOMEM);
+
+	/* Restore duplicated value so we can call lxc_iterate_parts() again. */
+	strcpy(value_dup, value);
+
+	lxc_iterate_parts(token, value_dup, ",") {
+		int ret;
+
+		gid_t group;
+
+		ret = lxc_safe_uint(token, &group);
+		if (ret)
+			return ret;
+
+		init_groups[iter++] = group;
+	}
+
+	lxc_conf->init_groups.size = num_groups;
+	lxc_conf->init_groups.list = move_ptr(init_groups);
+
+	return 0;
+}
+
 static int set_config_hooks(const char *key, const char *value,
 			    struct lxc_conf *lxc_conf, void *data)
 {
@@ -4278,6 +4327,26 @@ static int get_config_init_gid(const char *key, char *retv, int inlen,
 	return lxc_get_conf_int(c, retv, inlen, c->init_gid);
 }
 
+static int get_config_init_groups(const char *key, char *retv, int inlen,
+				  struct lxc_conf *c, void *data)
+{
+	int fulllen = 0, len;
+
+	if (!retv)
+		inlen = 0;
+	else
+		memset(retv, 0, inlen);
+
+	if (c->init_groups.size == 0)
+		return 0;
+
+	for (int i = 0; i < c->init_groups.size; i++)
+		strprint(retv, inlen, "%s%d", (i > 0) ? "," : "",
+			 c->init_groups.list[i]);
+
+	return fulllen;
+}
+
 static int get_config_ephemeral(const char *key, char *retv, int inlen,
 				struct lxc_conf *c, void *data)
 {
@@ -4964,6 +5033,14 @@ static inline int clr_config_init_gid(const char *key, struct lxc_conf *c,
 	return 0;
 }
 
+static inline int clr_config_init_groups(const char *key, struct lxc_conf *c,
+					 void *data)
+{
+	free_disarm(c->init_groups.list);
+	c->init_groups.size = 0;
+	return 0;
+}
+
 static inline int clr_config_ephemeral(const char *key, struct lxc_conf *c,
 				       void *data)
 {

src/lxc/start.c

@@ -1406,12 +1406,21 @@ static int do_start(void *data)
 	 * we switched to root in the new user namespace further above. Only
 	 * drop groups if we can, so ensure that we have necessary privilege.
 	 */
-	if (lxc_list_empty(&handler->conf->id_map))
+	if (lxc_list_empty(&handler->conf->id_map)) {
 		#if HAVE_LIBCAP
 		if (lxc_proc_cap_is_set(CAP_SETGID, CAP_EFFECTIVE))
 		#endif
+		{
+			if (handler->conf->init_groups.size > 0) {
+				if (!lxc_setgroups(handler->conf->init_groups.list,
+						   handler->conf->init_groups.size))
+					goto out_warn_father;
+			} else {
 				if (!lxc_drop_groups())
 					goto out_warn_father;
+			}
+		}
+	}
 
 	if (!lxc_switch_uid_gid(new_uid, new_gid))
 		goto out_warn_father;

src/tests/get_item.c

@@ -136,6 +136,34 @@ int main(int argc, char *argv[])
 	}
 	printf("lxc.init_gid returned %d %s\n", ret, v2);
 
+	if (!c->set_config_item(c, "lxc.init.groups", "")) {
+		fprintf(stderr, "%d: failed to set init_groups\n", __LINE__);
+		goto out;
+	}
+
+	if (!c->set_config_item(c, "lxc.init.groups", "10,20,foo,40")) {
+		printf("failed to set init_groups to '10,20,foo,40' as expected\n");
+	} else {
+		goto out;
+	}
+
+	if (!c->set_config_item(c, "lxc.init.groups", "10,20,30,40")) {
+		fprintf(stderr, "%d: failed to set init_groups\n", __LINE__);
+		goto out;
+	}
+
+	ret = c->get_config_item(c, "lxc.init.groups", v2, 255);
+	if (ret < 0) {
+		fprintf(stderr, "%d: get_config_item(lxc.init_gid) returned %d\n",
+			__LINE__, ret);
+		goto out;
+	}
+	ret = strcmp("10,20,30,40", v2);
+	printf("lxc.init_groups returned %d %s\n", ret, v2);
+	if (ret != 0) {
+		goto out;
+	}
+
 #define HNAME "hostname1"
 	// demonstrate proper usage:
 	char *alloced;