selftests/seccomp: check that a zombie leader doesn't affect others

Ensure that a dead thread leader doesn't prevent installing new filters
with SECCOMP_FILTER_FLAG_TSYNC from other threads.

Signed-off-by: Andrei Vagin <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Tycho Andersen <[email protected]>
Signed-off-by: Kees Cook <[email protected]>

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 390781d7c9518a9f455c454820b7a0e078a8ee20..e3f97f90d8db0f6fb8864d9641da44f9138c8b6b 100644 (file)
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -4809,6 +4809,83 @@ TEST(user_notification_wait_killable_fatal)
        EXPECT_EQ(SIGTERM, WTERMSIG(status));
 }
 
+struct tsync_vs_thread_leader_args {
+       pthread_t leader;
+};
+
+static void *tsync_vs_dead_thread_leader_sibling(void *_args)
+{
+       struct sock_filter allow_filter[] = {
+               BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+       };
+       struct sock_fprog allow_prog = {
+               .len = (unsigned short)ARRAY_SIZE(allow_filter),
+               .filter = allow_filter,
+       };
+       struct tsync_vs_thread_leader_args *args = _args;
+       void *retval;
+       long ret;
+
+       ret = pthread_join(args->leader, &retval);
+       if (ret)
+               exit(1);
+       if (retval != _args)
+               exit(2);
+       ret = seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_TSYNC, &allow_prog);
+       if (ret)
+               exit(3);
+
+       exit(0);
+}
+
+/*
+ * Ensure that a dead thread leader doesn't prevent installing new filters with
+ * SECCOMP_FILTER_FLAG_TSYNC from other threads.
+ */
+TEST(tsync_vs_dead_thread_leader)
+{
+       int status;
+       pid_t pid;
+       long ret;
+
+       ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+       ASSERT_EQ(0, ret) {
+               TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
+       }
+
+       pid = fork();
+       ASSERT_GE(pid, 0);
+
+       if (pid == 0) {
+               struct sock_filter allow_filter[] = {
+                       BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+               };
+               struct sock_fprog allow_prog = {
+                       .len = (unsigned short)ARRAY_SIZE(allow_filter),
+                       .filter = allow_filter,
+               };
+               struct  tsync_vs_thread_leader_args *args;
+               pthread_t sibling;
+
+               args = malloc(sizeof(*args));
+               ASSERT_NE(NULL, args);
+               args->leader = pthread_self();
+
+               ret = pthread_create(&sibling, NULL,
+                                    tsync_vs_dead_thread_leader_sibling, args);
+               ASSERT_EQ(0, ret);
+
+               /* Install a new filter just to the leader thread. */
+               ret = seccomp(SECCOMP_SET_MODE_FILTER, 0, &allow_prog);
+               ASSERT_EQ(0, ret);
+               pthread_exit(args);
+               exit(1);
+       }
+
+       EXPECT_EQ(pid, waitpid(pid, &status, 0));
+       EXPECT_EQ(0, status);
+}
+
 /*
  * TODO:
  * - expand NNP testing