Merge tag 'seccomp-v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull seccomp updates from Kees Cook:

 - Rework USER_NOTIF notification ordering and kill logic (Sargun
   Dhillon)

 - Improved PTRACE_O_SUSPEND_SECCOMP selftest (Jann Horn)

 - Gracefully handle failed unshare() in selftests (Yang Guang)

 - Spelling fix (Colin Ian King)

* tag 'seccomp-v5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  selftests/seccomp: Fix spelling mistake "Coud" -> "Could"
  selftests/seccomp: Add test for wait killable notifier
  selftests/seccomp: Refactor get_proc_stat to split out file reading code
  seccomp: Add wait_killable semantic to seccomp user notifier
  selftests/seccomp: Ensure that notifications come in FIFO order
  seccomp: Use FIFO semantics to order notifications
  selftests/seccomp: Add SKIP for failed unshare()
  selftests/seccomp: Test PTRACE_O_SUSPEND_SECCOMP without CAP_SYS_ADMIN

6 files changed, 482 insertions, 5 deletions

diff --git a/Documentation/userspace-api/seccomp_filter.rst b/Documentation/userspace-api/seccomp_filter.rst
index 539e9d4a4860..d1e2b9193f09 100644
--- a/Documentation/userspace-api/seccomp_filter.rst
+++ b/Documentation/userspace-api/seccomp_filter.rst
@@ -271,6 +271,16 @@ notifying process it will be replaced. The supervisor can also add an FD, and
 respond atomically by using the ``SECCOMP_ADDFD_FLAG_SEND`` flag and the return
 value will be the injected file descriptor number.
 
+The notifying process can be preempted, resulting in the notification being
+aborted. This can be problematic when trying to take actions on behalf of the
+notifying process that are long-running and typically retryable (mounting a
+filesytem). Alternatively, at filter installation time, the
+``SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV`` flag can be set. This flag makes it
+such that when a user notification is received by the supervisor, the notifying
+process will ignore non-fatal signals until the response is sent. Signals that
+are sent prior to the notification being received by userspace are handled
+normally.
+
 It is worth noting that ``struct seccomp_data`` contains the values of register
 arguments to the syscall, but does not contain pointers to memory. The task's
 memory is accessible to suitably privileged traces via ``ptrace()`` or
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 0c564e5d40ff..d31d76be4982 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -8,7 +8,8 @@
 					 SECCOMP_FILTER_FLAG_LOG | \
 					 SECCOMP_FILTER_FLAG_SPEC_ALLOW | \
 					 SECCOMP_FILTER_FLAG_NEW_LISTENER | \
-					 SECCOMP_FILTER_FLAG_TSYNC_ESRCH)
+					 SECCOMP_FILTER_FLAG_TSYNC_ESRCH | \
+					 SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV)
 
 /* sizeof() the first published struct seccomp_notif_addfd */
 #define SECCOMP_NOTIFY_ADDFD_SIZE_VER0 24
diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index 78074254ab98..0fdc6ef02b94 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -23,6 +23,8 @@
 #define SECCOMP_FILTER_FLAG_SPEC_ALLOW		(1UL << 2)
 #define SECCOMP_FILTER_FLAG_NEW_LISTENER	(1UL << 3)
 #define SECCOMP_FILTER_FLAG_TSYNC_ESRCH		(1UL << 4)
+/* Received notifications wait in killable state (only respond to fatal signals) */
+#define SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV	(1UL << 5)
 
 /*
  * All BPF programs must return a 32-bit value.
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index b5ac87f6dbd4..e9852d1b4a5e 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -200,6 +200,8 @@ static inline void seccomp_cache_prepare(struct seccomp_filter *sfilter)
  *	   the filter can be freed.
  * @cache: cache of arch/syscall mappings to actions
  * @log: true if all actions except for SECCOMP_RET_ALLOW should be logged
+ * @wait_killable_recv: Put notifying process in killable state once the
+ *			notification is received by the userspace listener.
  * @prev: points to a previously installed, or inherited, filter
  * @prog: the BPF program to evaluate
  * @notif: the struct that holds all notification related information
@@ -220,6 +222,7 @@ struct seccomp_filter {
 	refcount_t refs;
 	refcount_t users;
 	bool log;
+	bool wait_killable_recv;
 	struct action_cache cache;
 	struct seccomp_filter *prev;
 	struct bpf_prog *prog;
@@ -893,6 +896,10 @@ static long seccomp_attach_filter(unsigned int flags,
 	if (flags & SECCOMP_FILTER_FLAG_LOG)
 		filter->log = true;
 
+	/* Set wait killable flag, if present. */
+	if (flags & SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV)
+		filter->wait_killable_recv = true;
+
 	/*
 	 * If there is an existing filter, make it the prev and don't drop its
 	 * task reference.
@@ -1080,6 +1087,12 @@ static void seccomp_handle_addfd(struct seccomp_kaddfd *addfd, struct seccomp_kn
 	complete(&addfd->completion);
 }
 
+static bool should_sleep_killable(struct seccomp_filter *match,
+				  struct seccomp_knotif *n)
+{
+	return match->wait_killable_recv && n->state == SECCOMP_NOTIFY_SENT;
+}
+
 static int seccomp_do_user_notification(int this_syscall,
 					struct seccomp_filter *match,
 					const struct seccomp_data *sd)
@@ -1100,7 +1113,7 @@ static int seccomp_do_user_notification(int this_syscall,
 	n.data = sd;
 	n.id = seccomp_next_notify_id(match);
 	init_completion(&n.ready);
-	list_add(&n.list, &match->notif->notifications);
+	list_add_tail(&n.list, &match->notif->notifications);
 	INIT_LIST_HEAD(&n.addfd);
 
 	up(&match->notif->request);
@@ -1110,11 +1123,25 @@ static int seccomp_do_user_notification(int this_syscall,
 	 * This is where we wait for a reply from userspace.
 	 */
 	do {
+		bool wait_killable = should_sleep_killable(match, &n);
+
 		mutex_unlock(&match->notify_lock);
-		err = wait_for_completion_interruptible(&n.ready);
+		if (wait_killable)
+			err = wait_for_completion_killable(&n.ready);
+		else
+			err = wait_for_completion_interruptible(&n.ready);
 		mutex_lock(&match->notify_lock);
-		if (err != 0)
+
+		if (err != 0) {
+			/*
+			 * Check to see if the notifcation got picked up and
+			 * whether we should switch to wait killable.
+			 */
+			if (!wait_killable && should_sleep_killable(match, &n))
+				continue;
+
 			goto interrupted;
+		}
 
 		addfd = list_first_entry_or_null(&n.addfd,
 						 struct seccomp_kaddfd, list);
@@ -1484,6 +1511,9 @@ out:
 		mutex_lock(&filter->notify_lock);
 		knotif = find_notification(filter, unotif.id);
 		if (knotif) {
+			/* Reset the process to make sure it's not stuck */
+			if (should_sleep_killable(filter, knotif))
+				complete(&knotif->ready);
 			knotif->state = SECCOMP_NOTIFY_INIT;
 			up(&filter->notif->request);
 		}
@@ -1829,6 +1859,14 @@ static long seccomp_set_mode_filter(unsigned int flags,
 	    ((flags & SECCOMP_FILTER_FLAG_TSYNC_ESRCH) == 0))
 		return -EINVAL;
 
+	/*
+	 * The SECCOMP_FILTER_FLAG_WAIT_KILLABLE_SENT flag doesn't make sense
+	 * without the SECCOMP_FILTER_FLAG_NEW_LISTENER flag.
+	 */
+	if ((flags & SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV) &&
+	    ((flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) == 0))
+		return -EINVAL;
+
 	/* Prepare the new filter before holding any locks. */
 	prepared = seccomp_prepare_user_filter(filter);
 	if (IS_ERR(prepared))
diff --git a/tools/testing/selftests/seccomp/Makefile b/tools/testing/selftests/seccomp/Makefile
index 585f7a0c10cb..f017c382c036 100644
--- a/tools/testing/selftests/seccomp/Makefile
+++ b/tools/testing/selftests/seccomp/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += -Wl,-no-as-needed -Wall -isystem ../../../../usr/include/
 LDFLAGS += -lpthread
+LDLIBS += -lcap
 
 TEST_GEN_PROGS := seccomp_bpf seccomp_benchmark
 include ../lib.mk
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 313bb0cbfb1e..136df5b76319 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -46,6 +46,7 @@
 #include <sys/ioctl.h>
 #include <linux/kcmp.h>
 #include <sys/resource.h>
+#include <sys/capability.h>
 
 #include <unistd.h>
 #include <sys/syscall.h>
@@ -59,6 +60,8 @@
 #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 +271,10 @@ 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)
 {
@@ -3742,7 +3749,10 @@ TEST(user_notification_fault_recv)
 	struct seccomp_notif req = {};
 	struct seccomp_notif_resp resp = {};
 
-	ASSERT_EQ(unshare(CLONE_NEWUSER), 0);
+	ASSERT_EQ(unshare(CLONE_NEWUSER), 0) {
+		if (errno == EINVAL)
+			SKIP(return, "kernel missing CLONE_NEWUSER support");
+	}
 
 	listener = user_notif_syscall(__NR_getppid,
 				      SECCOMP_FILTER_FLAG_NEW_LISTENER);
@@ -4231,6 +4241,421 @@ TEST(user_notification_addfd_rlimit)
 	close(memfd);
 }
 
+/* Make sure PTRACE_O_SUSPEND_SECCOMP requires CAP_SYS_ADMIN. */
+FIXTURE(O_SUSPEND_SECCOMP) {
+	pid_t pid;
+};
+
+FIXTURE_SETUP(O_SUSPEND_SECCOMP)
+{
+	ERRNO_FILTER(block_read, E2BIG);
+	cap_value_t cap_list[] = { CAP_SYS_ADMIN };
+	cap_t caps;
+
+	self->pid = 0;
+
+	/* make sure we don't have CAP_SYS_ADMIN */
+	caps = cap_get_proc();
+	ASSERT_NE(NULL, caps);
+	ASSERT_EQ(0, cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_list, CAP_CLEAR));
+	ASSERT_EQ(0, cap_set_proc(caps));
+	cap_free(caps);
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+	ASSERT_EQ(0, prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_block_read));
+
+	self->pid = fork();
+	ASSERT_GE(self->pid, 0);
+
+	if (self->pid == 0) {
+		while (1)
+			pause();
+		_exit(127);
+	}
+}
+
+FIXTURE_TEARDOWN(O_SUSPEND_SECCOMP)
+{
+	if (self->pid)
+		kill(self->pid, SIGKILL);
+}
+
+TEST_F(O_SUSPEND_SECCOMP, setoptions)
+{
+	int wstatus;
+
+	ASSERT_EQ(0, ptrace(PTRACE_ATTACH, self->pid, NULL, 0));
+	ASSERT_EQ(self->pid, wait(&wstatus));
+	ASSERT_EQ(-1, ptrace(PTRACE_SETOPTIONS, self->pid, NULL, PTRACE_O_SUSPEND_SECCOMP));
+	if (errno == EINVAL)
+		SKIP(return, "Kernel does not support PTRACE_O_SUSPEND_SECCOMP (missing CONFIG_CHECKPOINT_RESTORE?)");
+	ASSERT_EQ(EPERM, errno);
+}
+
+TEST_F(O_SUSPEND_SECCOMP, seize)
+{
+	int ret;
+
+	ret = ptrace(PTRACE_SEIZE, self->pid, NULL, PTRACE_O_SUSPEND_SECCOMP);
+	ASSERT_EQ(-1, ret);
+	if (errno == EINVAL)
+		SKIP(return, "Kernel does not support PTRACE_O_SUSPEND_SECCOMP (missing CONFIG_CHECKPOINT_RESTORE?)");
+	ASSERT_EQ(EPERM, errno);
+}
+
+/*
+ * get_nth - Get the nth, space separated entry in a file.
+ *
+ * Returns the length of the read field.
+ * Throws error if field is zero-lengthed.
+ */
+static ssize_t get_nth(struct __test_metadata *_metadata, const char *path,
+		     const unsigned int position, char **entry)
+{
+	char *line = NULL;
+	unsigned int i;
+	ssize_t nread;
+	size_t len = 0;
+	FILE *f;
+
+	f = fopen(path, "r");
+	ASSERT_NE(f, NULL) {
+		TH_LOG("Could not open %s: %s", path, strerror(errno));
+	}
+
+	for (i = 0; i < position; i++) {
+		nread = getdelim(&line, &len, ' ', f);
+		ASSERT_GE(nread, 0) {
+			TH_LOG("Failed to read %d entry in file %s", i, path);
+		}
+	}
+	fclose(f);
+
+	ASSERT_GT(nread, 0) {
+		TH_LOG("Entry in file %s had zero length", path);
+	}
+
+	*entry = line;
+	return nread - 1;
+}
+
+/* For a given PID, get the task state (D, R, etc...) */
+static char get_proc_stat(struct __test_metadata *_metadata, pid_t pid)
+{
+	char proc_path[100] = {0};
+	char status;
+	char *line;
+
+	snprintf(proc_path, sizeof(proc_path), "/proc/%d/stat", pid);
+	ASSERT_EQ(get_nth(_metadata, proc_path, 3, &line), 1);
+
+	status = *line;
+	free(line);
+
+	return status;
+}
+
+TEST(user_notification_fifo)
+{
+	struct seccomp_notif_resp resp = {};
+	struct seccomp_notif req = {};
+	int i, status, listener;
+	pid_t pid, pids[3];
+	__u64 baseid;
+	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!");
+	}
+
+	/* Setup a listener */
+	listener = user_notif_syscall(__NR_getppid,
+				      SECCOMP_FILTER_FLAG_NEW_LISTENER);
+	ASSERT_GE(listener, 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		ret = syscall(__NR_getppid);
+		exit(ret != USER_NOTIF_MAGIC);
+	}
+
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+	baseid = req.id + 1;
+
+	resp.id = req.id;
+	resp.error = 0;
+	resp.val = USER_NOTIF_MAGIC;
+
+	/* check that we make sure flags == 0 */
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0);
+
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(true, WIFEXITED(status));
+	EXPECT_EQ(0, WEXITSTATUS(status));
+
+	/* Start children, and generate notifications */
+	for (i = 0; i < ARRAY_SIZE(pids); i++) {
+		pid = fork();
+		if (pid == 0) {
+			ret = syscall(__NR_getppid);
+			exit(ret != USER_NOTIF_MAGIC);
+		}
+		pids[i] = pid;
+	}
+
+	/* This spins until all of the children are sleeping */
+restart_wait:
+	for (i = 0; i < ARRAY_SIZE(pids); i++) {
+		if (get_proc_stat(_metadata, pids[i]) != 'S') {
+			nanosleep(&delay, NULL);
+			goto restart_wait;
+		}
+	}
+
+	/* Read the notifications in order (and respond) */
+	for (i = 0; i < ARRAY_SIZE(pids); i++) {
+		memset(&req, 0, sizeof(req));
+		EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+		EXPECT_EQ(req.id, baseid + i);
+		resp.id = req.id;
+		EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0);
+	}
+
+	/* Make sure notifications were received */
+	for (i = 0; i < ARRAY_SIZE(pids); i++) {
+		EXPECT_EQ(waitpid(pids[i], &status, 0), pids[i]);
+		EXPECT_EQ(true, WIFEXITED(status));
+		EXPECT_EQ(0, WEXITSTATUS(status));
+	}
+}
+
+/* get_proc_syscall - Get the syscall in progress for a given pid
+ *
+ * Returns the current syscall number for a given process
+ * Returns -1 if not in syscall (running or blocked)
+ */
+static long get_proc_syscall(struct __test_metadata *_metadata, int pid)
+{
+	char proc_path[100] = {0};
+	long ret = -1;
+	ssize_t nread;
+	char *line;
+
+	snprintf(proc_path, sizeof(proc_path), "/proc/%d/syscall", pid);
+	nread = get_nth(_metadata, proc_path, 1, &line);
+	ASSERT_GT(nread, 0);
+
+	if (!strncmp("running", line, MIN(7, nread)))
+		ret = strtol(line, NULL, 16);
+
+	free(line);
+	return ret;
+}
+
+/* Ensure non-fatal signals prior to receive are unmodified */
+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 non-fatal sigaction without SA_RESTART */
+		if (sigaction(SIGUSR1, &new_action, NULL)) {
+			perror("sigaction");
+			exit(1);
+		}
+
+		ret = syscall(__NR_getppid);
+		/* Make sure we got a return from a signal interruption */
+		exit(ret != -1 || errno != EINTR);
+	}
+
+	/*
+	 * Make sure we've gotten to the seccomp user notification wait
+	 * from getppid prior to sending any signals
+	 */
+	while (get_proc_syscall(_metadata, pid) != __NR_getppid &&
+	       get_proc_stat(_metadata, pid) != 'S')
+		nanosleep(&delay, NULL);
+
+	/* Send non-fatal kill signal */
+	EXPECT_EQ(kill(pid, SIGUSR1), 0);
+
+	/* wait for process to exit (exit checks for EINTR) */
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(true, WIFEXITED(status));
+	EXPECT_EQ(0, WEXITSTATUS(status));
+
+	EXPECT_EQ(read(sk_pair[0], &c, 1), 1);
+}
+
+/* Ensure non-fatal signals after receive are blocked */
+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);
+	}
+
+	/*
+	 * Get the notification, to make move the notifying process into a
+	 * non-preemptible (TASK_KILLABLE) state.
+	 */
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+	/* Send non-fatal kill signal */
+	EXPECT_EQ(kill(pid, SIGUSR1), 0);
+
+	/*
+	 * Make sure the task enters moves to TASK_KILLABLE by waiting for
+	 * D (Disk Sleep) state after receiving non-fatal signal.
+	 */
+	while (get_proc_stat(_metadata, pid) != 'D')
+		nanosleep(&delay, NULL);
+
+	resp.id = req.id;
+	resp.val = USER_NOTIF_MAGIC;
+	/* Make sure the notification is found and able to be replied to */
+	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);
+	/* wait for process to exit (exit checks for USER_NOTIF_MAGIC) */
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(true, WIFEXITED(status));
+	EXPECT_EQ(0, WEXITSTATUS(status));
+}
+
+/* Ensure fatal signals after receive are not blocked */
+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 as it should get a SIGTERM */
+		syscall(__NR_getppid);
+		exit(1);
+	}
+
+	while (get_proc_stat(_metadata, pid) != 'S')
+		nanosleep(&delay, NULL);
+
+	/*
+	 * Get the notification, to make move the notifying process into a
+	 * non-preemptible (TASK_KILLABLE) state.
+	 */
+	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+	/* Kill the process with a fatal signal */
+	EXPECT_EQ(kill(pid, SIGTERM), 0);
+
+	/*
+	 * Wait for the process to exit, and make sure the process terminated
+	 * due to the SIGTERM signal.
+	 */
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(true, WIFSIGNALED(status));
+	EXPECT_EQ(SIGTERM, WTERMSIG(status));
+}
+
 /*
  * TODO:
  * - expand NNP testing