restore: Skip setgroups() when already correct.

Skip calling setgroups() when the list of auxiliary groups already has the values we want. This allows restoring into an unprivileged user namespace where setgroups() is disabled. From: Ambrose Feinstein <[email protected]> Signed-off-by: Michał Mirosław <[email protected]>
checkpoint-restore · Jul 22, 2023 · 53dd6ba · 53dd6ba
1 parent b9f360b
commit 53dd6ba
Showing 1 changed file with 18 additions and 4 deletions.
diff --git a/criu/pie/restorer.c b/criu/pie/restorer.c
@@ -51,6 +51,11 @@
 #include "shmem.h"
 #include "restorer.h"
 
+/*
+ * sys_getgroups() buffer size. Not too much, to avoid stack overflow.
+ */
+#define MAX_GETGROUPS_CHECKED (512 / sizeof(unsigned int))
+
 #ifndef PR_SET_PDEATHSIG
 #define PR_SET_PDEATHSIG 1
 #endif
@@ -198,10 +203,19 @@ static int restore_creds(struct thread_creds_args *args, int procfd, int lsm_typ
 	 * Setup supplementary group IDs early.
 	 */
 	if (args->groups) {
-		ret = sys_setgroups(ce->n_groups, args->groups);
-		if (ret) {
-			pr_err("Can't setup supplementary group IDs: %d\n", ret);
-			return -1;
+		/*
+		 * We may be in an unprivileged user namespace where setgroups
+		 * is disabled.  If the current list of groups is already what
+		 * we want, skip the call to setgroups.
+		 */
+		unsigned int gids[MAX_GETGROUPS_CHECKED];
+		int n = sys_getgroups(MAX_GETGROUPS_CHECKED, gids);
+		if (n != ce->n_groups || memcmp(gids, args->groups, n * sizeof(*gids))) {
+			ret = sys_setgroups(ce->n_groups, args->groups);
+			if (ret) {
+				pr_err("Can't setgroups([%zu gids]): %d\n", ce->n_groups, ret);
+				return -1;
+			}
 		}
 	}