3 files changed, 36 insertions, 5 deletions

diff --git a/src/config.c b/src/config.c
index 2d387f3..b857d60 100644
--- a/src/config.c
+++ b/src/config.c
@@ -848,6 +848,20 @@ static void configure_user(fastd_context_t *ctx, fastd_config_t *conf) {
 
 		conf->gid = grpr->gr_gid;
 	}
+
+	if (conf->user) {
+		int ngroups = 0;
+		if (getgrouplist(conf->user, conf->gid, NULL, &ngroups) < 0) {
+			/* the user has supplementary groups */
+
+			conf->groups = calloc(ngroups, sizeof(gid_t));
+			if (getgrouplist(conf->user, conf->gid, conf->groups, &ngroups) < 0)
+				exit_errno(ctx, "getgrouplist");
+
+			conf->n_groups = ngroups;
+		}
+	}
+
 }
 
 void fastd_configure(fastd_context_t *ctx, fastd_config_t *conf, int argc, char *const argv[]) {
@@ -1036,6 +1050,7 @@ void fastd_config_release(fastd_context_t *ctx, fastd_config_t *conf) {
 
 	free(conf->user);
 	free(conf->group);
+	free(conf->groups);
 	free(conf->ifname);
 	free(conf->secret);
 	free(conf->on_up);
diff --git a/src/fastd.c b/src/fastd.c
index 22d64b9..3b72922 100644
--- a/src/fastd.c
+++ b/src/fastd.c
@@ -1037,11 +1037,6 @@ static void set_user(fastd_context_t *ctx) {
 		if (setgid(ctx->conf->gid) < 0)
 			exit_errno(ctx, "setgid");
 
-		if (setgroups(1, &ctx->conf->gid) < 0) {
-			if (errno != EPERM)
-				pr_debug_errno(ctx, "setgroups");
-		}
-
 		if (setuid(ctx->conf->uid) < 0)
 			exit_errno(ctx, "setuid");
 
@@ -1049,6 +1044,21 @@ static void set_user(fastd_context_t *ctx) {
 	}
 }
 
+static void set_groups(fastd_context_t *ctx) {
+	if (ctx->conf->groups) {
+		if (setgroups(ctx->conf->n_groups, ctx->conf->groups) < 0) {
+			if (errno != EPERM)
+				pr_debug_errno(ctx, "setgroups");
+		}
+	}
+	else if (ctx->conf->user || ctx->conf->group) {
+		if (setgroups(1, &ctx->conf->gid) < 0) {
+			if (errno != EPERM)
+				pr_debug_errno(ctx, "setgroups");
+		}
+	}
+}
+
 static void drop_caps(fastd_context_t *ctx) {
 	set_user(ctx);
 	fastd_cap_drop(ctx);
@@ -1089,6 +1099,9 @@ int main(int argc, char *argv[]) {
 
 	fastd_cap_init(&ctx);
 
+	/* change groups early as the can be relevant for file access (for PID file & log files) */
+	set_groups(&ctx);
+
 	crypto_init(&ctx);
 
 	init_sockets(&ctx);
diff --git a/src/fastd.h b/src/fastd.h
index df84c97..5323c1c 100644
--- a/src/fastd.h
+++ b/src/fastd.h
@@ -199,8 +199,11 @@ struct fastd_config {
 
 	char *user;
 	char *group;
+
 	uid_t uid;
 	gid_t gid;
+	size_t n_groups;
+	gid_t *groups;
 
 	const fastd_protocol_t *protocol;
 	const fastd_method_t *methods[MAX_METHODS];