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-rw-r--r--src/timesync/timesyncd.c82
1 files changed, 82 insertions, 0 deletions
diff --git a/src/timesync/timesyncd.c b/src/timesync/timesyncd.c
index aefbd27c7b..33c04df933 100644
--- a/src/timesync/timesyncd.c
+++ b/src/timesync/timesyncd.c
@@ -33,6 +33,9 @@
#include <sys/timex.h>
#include <sys/socket.h>
#include <resolv.h>
+#include <sys/prctl.h>
+#include <sys/types.h>
+#include <grp.h>
#include "missing.h"
#include "util.h"
@@ -49,6 +52,7 @@
#include "sd-network.h"
#include "event-util.h"
#include "network-util.h"
+#include "capability.h"
#include "timesyncd.h"
#define TIME_T_MAX (time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)
@@ -1138,6 +1142,80 @@ static int manager_network_monitor_listen(Manager *m) {
return 0;
}
+static int drop_priviliges(void) {
+ static const cap_value_t bits[] = {
+ CAP_SYS_TIME,
+ };
+
+ _cleanup_cap_free_ cap_t d = NULL;
+ const char *name = "systemd-timesync";
+ uid_t uid;
+ gid_t gid;
+ int r;
+
+ /* Unfortunately we cannot leave privilige dropping to PID 1
+ * here, since we want to run as user but want to keep te
+ * CAP_SYS_TIME capability. Since file capabilities have been
+ * introduced this cannot be done across exec() anymore,
+ * unless our binary has the capability configured in the file
+ * system, which we want to avoid. */
+
+ r = get_user_creds(&name, &uid, &gid, NULL, NULL);
+ if (r < 0) {
+ log_error("Cannot resolve user name %s: %s", name, strerror(-r));
+ return r;
+ }
+
+ if (setresgid(gid, gid, gid) < 0) {
+ log_error("Failed change group ID: %m");
+ return -errno;
+ }
+
+ if (setgroups(0, NULL) < 0) {
+ log_error("Failed to drop auxiliary groups list: %m");
+ return -errno;
+ }
+
+ if (prctl(PR_SET_KEEPCAPS, 1) < 0) {
+ log_error("Failed to enable keep capabilities flag: %m");
+ return -errno;
+ }
+
+ r = setresuid(uid, uid, uid);
+ if (r < 0) {
+ log_error("Failed change user ID: %m");
+ return -errno;
+ }
+
+ if (prctl(PR_SET_KEEPCAPS, 0) < 0) {
+ log_error("Failed to disable keep capabilities flag: %m");
+ return -errno;
+ }
+
+ r = capability_bounding_set_drop(~(1ULL << CAP_SYS_TIME), true);
+ if (r < 0) {
+ log_error("Failed to drop capabilities: %s", strerror(-r));
+ return r;
+ }
+
+ d = cap_init();
+ if (!d)
+ return log_oom();
+
+ if (cap_set_flag(d, CAP_EFFECTIVE, ELEMENTSOF(bits), bits, CAP_SET) < 0 ||
+ cap_set_flag(d, CAP_PERMITTED, ELEMENTSOF(bits), bits, CAP_SET) < 0) {
+ log_error("Failed to enable capabilities bits: %m");
+ return -errno;
+ }
+
+ if (cap_set_proc(d) < 0) {
+ log_error("Failed to increase capabilities: %m");
+ return -errno;
+ }
+
+ return 0;
+}
+
int main(int argc, char *argv[]) {
_cleanup_manager_free_ Manager *m = NULL;
int r;
@@ -1154,6 +1232,10 @@ int main(int argc, char *argv[]) {
umask(0022);
+ r = drop_priviliges();
+ if (r < 0)
+ goto out;
+
assert_se(sigprocmask_many(SIG_BLOCK, SIGTERM, SIGINT, -1) == 0);
r = manager_new(&m);