Re: [PATCH v3 2/2] selftests/seccomp: Add test for wait killable notifier

[Kees Cook <keescook@chromium.org>]

On Thu, Apr 28, 2022 at 07:31:13PM -0700, Sargun Dhillon wrote:
> This verifies that if a filter is set up with the wait killable feature
> that it obeys the semantics that non-fatal signals are ignored during
> a notification after the notification is received.
> 
> Cases tested:
>  * Non-fatal signal prior to receive
>  * Non-fatal signal during receive
>  * Fatal signal after receive
> 
> The pre-receive signal handling is tested elsewhere, and that codepath
> remains unchanged.
> 
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> ---
>  tools/testing/selftests/seccomp/seccomp_bpf.c | 240 ++++++++++++++++++
>  1 file changed, 240 insertions(+)
> 
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index 9d126d7fabdb..825b179b6751 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -59,6 +59,8 @@
>  #define SKIP(s, ...)	XFAIL(s, ##__VA_ARGS__)
>  #endif
>  
> +#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
> +
>  #ifndef PR_SET_PTRACER
>  # define PR_SET_PTRACER 0x59616d61
>  #endif
> @@ -268,6 +270,10 @@ struct seccomp_notif_addfd_big {
>  #define SECCOMP_FILTER_FLAG_TSYNC_ESRCH (1UL << 4)
>  #endif
>  
> +#ifndef SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV
> +#define SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV (1UL << 5)
> +#endif
> +
>  #ifndef seccomp
>  int seccomp(unsigned int op, unsigned int flags, void *args)
>  {
> @@ -4231,6 +4237,240 @@ TEST(user_notification_addfd_rlimit)
>  	close(memfd);
>  }
>  
> +static char get_proc_stat(int pid)
> +{
> +	char proc_path[100] = { 0 };
> +	char *line = NULL;
> +	size_t len = 0;
> +	ssize_t nread;
> +	char status;
> +	FILE *f;
> +	int i;
> +
> +	snprintf(proc_path, sizeof(proc_path), "/proc/%d/stat", pid);
> +	f = fopen(proc_path, "r");
> +	if (f == NULL)
> +		ksft_exit_fail_msg("%s - Could not open %s\n", strerror(errno),
> +				   proc_path);
> +
> +	for (i = 0; i < 3; i++) {
> +		nread = getdelim(&line, &len, ' ', f);
> +		if (nread <= 0)
> +			ksft_exit_fail_msg("Failed to read status: %s\n",
> +					   strerror(errno));
> +	}
> +
> +	status = *line;
> +	free(line);
> +	fclose(f);
> +
> +	return status;
> +}
> +
> +/* Returns -1 if not in syscall (running or blocked) */
> +static long get_proc_syscall(int pid)
> +{
> +	char proc_path[100] = { 0 };
> +	char *line = NULL;
> +	size_t len = 0;
> +	ssize_t nread;
> +	long ret = -1;
> +	FILE *f;
> +
> +	snprintf(proc_path, sizeof(proc_path), "/proc/%d/syscall", pid);
> +	f = fopen(proc_path, "r");
> +	if (f == NULL)
> +		ksft_exit_fail_msg("%s - Could not open %s\n", strerror(errno),
> +				   proc_path);
> +
> +	nread = getdelim(&line, &len, ' ', f);
> +	if (nread <= 0)
> +		ksft_exit_fail_msg("Failed to read status: %s\n",
> +				   strerror(errno));
> +
> +	if (!strncmp("running", line, MIN(7, nread)))
> +		ret = strtol(line, NULL, 16);
> +
> +	free(line);
> +	fclose(f);
> +
> +	return ret;
> +}

I think these should be merged as they're almost entirely the same. The
differences are position wanted and file read. Also, passing metadata in
will let it break out on errors.

static char *get_proc_delim(struct __test_metadata *_metadata,
			    unsigned int pid, const char *name,
			    const unsigned int position)
{
	char proc_path[100] = { 0 };
	char *line = NULL;
	size_t len = 0;
	ssize_t nread;
	unsigned int i;
	FILE *f;

	snprintf(proc_path, sizeof(proc_path), "/proc/%d/%s", pid, name);
	f = fopen(proc_path, "r");
	ASSERT_NE(f, NULL) {
		TH_LOG("%s: %s\n", proc_path, strerror(errno));
	}

	for (i = 0; i < position; i++) {
		nread = getdelim(&line, &len, ' ', f);
		ASSERT_GE(nread, 0) {
			TH_LOG("%s: %s\n", proc_path, strerror(errno));
		}
	}
	fclose(f);

	return line;
}

static char get_proc_status(struct __test_metadata *_metadata, int pid)
{
	char status;
	char *item;

	item = get_proc_delim(_metadata,, pid, "stat", 3);
	status = *line;
	free(line);

	return status;
}

static long get_proc_syscall(struct __test_metadata *_metadata, int pid)
{
	char *item;
	long syscall = -1;

	item = get_proc_delim(_metadata, pid, "syscall", 1);
	syscall = strtol(line, item, 16);

	if (!strcmp("running", item)) {
		syscall = strtol(line, NULL, 16);
		ASSERT_NE(syscall, LONG_MIN);
		ASSERT_NE(syscall, LONG_MAX);
	}
	free(item);

	return syscall;
}

> +
> +TEST(user_notification_wait_killable_pre_notification)
> +{
> +	struct sigaction new_action = {
> +		.sa_handler = signal_handler,
> +	};
> +	int listener, status, sk_pair[2];
> +	pid_t pid;
> +	long ret;
> +	char c;
> +	/* 100 ms */
> +	struct timespec delay = { .tv_nsec = 100000000 };
> +
> +	ASSERT_EQ(sigemptyset(&new_action.sa_mask), 0);
> +
> +	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!");
> +	}
> +
> +	ASSERT_EQ(socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sk_pair), 0);
> +
> +
> +	listener = user_notif_syscall(__NR_getppid,
> +				      SECCOMP_FILTER_FLAG_NEW_LISTENER |
> +				      SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV);
> +	ASSERT_GE(listener, 0);
> +
> +	/*
> +	 * Check that we can kill the process with SIGUSR1 prior to receiving
> +	 * the notification. SIGUSR1 is wired up to a custom signal handler,
> +	 * and make sure it gets called.
> +	 */
> +	pid = fork();
> +	ASSERT_GE(pid, 0);
> +
> +	if (pid == 0) {
> +		close(sk_pair[0]);
> +		handled = sk_pair[1];
> +
> +		/* Setup the sigaction without SA_RESTART */
> +		if (sigaction(SIGUSR1, &new_action, NULL)) {
> +			perror("sigaction");
> +			exit(1);
> +		}
> +
> +		ret = syscall(__NR_getppid);
> +		exit(ret != -1 || errno != EINTR);
> +	}

I could use more comments in here. IIUC, they would be:

> +

	/* Wait for process to block for user_notif in getppid */
> +	while (get_proc_syscall(pid) != __NR_getppid &&
> +	       get_proc_stat(pid) != 'S')
> +		nanosleep(&delay, NULL);
> +

	/* Kill process */
> +	EXPECT_EQ(kill(pid, SIGUSR1), 0);
> +

	/*
	 * Make sure the process ends happily (i.e. its getppid()
	 * failed with EINTR.
	 */
> +	EXPECT_EQ(waitpid(pid, &status, 0), pid);
> +	EXPECT_EQ(true, WIFEXITED(status));
> +	EXPECT_EQ(0, WEXITSTATUS(status));
> +

	/* Also make sure the signal handler fired. */
> +	EXPECT_EQ(read(sk_pair[0], &c, 1), 1);
> +}
> +
> +TEST(user_notification_wait_killable)
> +{
> +	struct sigaction new_action = {
> +		.sa_handler = signal_handler,
> +	};
> +	struct seccomp_notif_resp resp = {};
> +	struct seccomp_notif req = {};
> +	int listener, status, sk_pair[2];
> +	pid_t pid;
> +	long ret;
> +	char c;
> +	/* 100 ms */
> +	struct timespec delay = { .tv_nsec = 100000000 };
> +
> +	ASSERT_EQ(sigemptyset(&new_action.sa_mask), 0);
> +
> +	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!");
> +	}
> +
> +	ASSERT_EQ(socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sk_pair), 0);
> +
> +	listener = user_notif_syscall(__NR_getppid,
> +				      SECCOMP_FILTER_FLAG_NEW_LISTENER |
> +				      SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV);
> +	ASSERT_GE(listener, 0);
> +
> +	pid = fork();
> +	ASSERT_GE(pid, 0);
> +
> +	if (pid == 0) {
> +		close(sk_pair[0]);
> +		handled = sk_pair[1];
> +
> +		/* Setup the sigaction without SA_RESTART */
> +		if (sigaction(SIGUSR1, &new_action, NULL)) {
> +			perror("sigaction");
> +			exit(1);
> +		}
> +
> +		/* Make sure that the syscall is completed (no EINTR) */
> +		ret = syscall(__NR_getppid);
> +		exit(ret != USER_NOTIF_MAGIC);
> +	}
> +
> +	while (get_proc_syscall(pid) != __NR_getppid &&
> +	       get_proc_stat(pid) != 'S')
> +		nanosleep(&delay, NULL);
> +
> +	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
> +	/* Kill the process to make sure it enters the wait_killable state */
> +	EXPECT_EQ(kill(pid, SIGUSR1), 0);
> +
> +	/* TASK_KILLABLE is considered D (Disk Sleep) state */
> +	while (get_proc_stat(pid) != 'D')
> +		nanosleep(&delay, NULL);

Should a NOWAIT waitpid() happen in this loop to make sure this doesn't
spin forever?

i.e. running these tests on a kernel that doesn't have the support
shouldn't hang -- yes it'll time out eventually but that's annoying. ;)

> +
> +	resp.id = req.id;
> +	resp.val = USER_NOTIF_MAGIC;
> +	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0);
> +
> +	/*
> +	 * Make sure that the signal handler does get called once we're back in
> +	 * userspace.
> +	 */
> +	EXPECT_EQ(read(sk_pair[0], &c, 1), 1);
> +	EXPECT_EQ(waitpid(pid, &status, 0), pid);
> +	EXPECT_EQ(true, WIFEXITED(status));
> +	EXPECT_EQ(0, WEXITSTATUS(status));
> +}
> +
> +TEST(user_notification_wait_killable_fatal)
> +{
> +	struct seccomp_notif req = {};
> +	int listener, status;
> +	pid_t pid;
> +	long ret;
> +	/* 100 ms */
> +	struct timespec delay = { .tv_nsec = 100000000 };
> +
> +	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!");
> +	}
> +
> +	listener = user_notif_syscall(__NR_getppid,
> +				      SECCOMP_FILTER_FLAG_NEW_LISTENER |
> +				      SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV);
> +	ASSERT_GE(listener, 0);
> +
> +	pid = fork();
> +	ASSERT_GE(pid, 0);
> +
> +	if (pid == 0) {
> +		/* This should never complete */
> +		syscall(__NR_getppid);
> +		exit(1);
> +	}
> +
> +	while (get_proc_stat(pid) != 'S')
> +		nanosleep(&delay, NULL);
> +
> +	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
> +	/* Kill the process with a fatal signal */
> +	EXPECT_EQ(kill(pid, SIGTERM), 0);
> +
> +	EXPECT_EQ(waitpid(pid, &status, 0), pid);
> +	EXPECT_EQ(true, WIFSIGNALED(status));
> +	EXPECT_EQ(SIGTERM, WTERMSIG(status));
> +}

Should there be a test validating the inverse of this, as in _without_
SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV, how should the above tests
behave?

Otherwise, looks good! Yay tests!

-- 
Kees Cook