[PATCH 3/3] selftests/seccomp: Test NOTIF_RECV empty/dead errors

[Jann Horn]

Test that SECCOMP_IOCTL_NOTIF_RECV on a seccomp fd with zero users returns
-ENOTCONN, both in blocking and in non-blocking mode.
Also test that SECCOMP_IOCTL_NOTIF_RECV on a seccomp fd with no active
notifications returns -ENOENT in non-blocking mode.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 127 ++++++++++++++++++
 1 file changed, 127 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 5318f9cb1aec..8214c431ad4b 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -28,6 +28,7 @@
 #include <linux/prctl.h>
 #include <linux/ptrace.h>
 #include <linux/seccomp.h>
+#include <linux/futex.h>
 #include <pthread.h>
 #include <semaphore.h>
 #include <signal.h>
@@ -315,6 +316,35 @@ static int __filecmp(pid_t pid1, pid_t pid2, int fd1, int fd2)
 	}						\
 	_ret; })
 
+static void store_and_wake(int *ptr, int value)
+{
+	__atomic_store(ptr, &value, __ATOMIC_RELEASE);
+	if (syscall(__NR_futex, ptr, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) == -1) {
+		perror("FUTEX_WAKE failed unexpectedly");
+		exit(EXIT_FAILURE);
+	}
+}
+
+static int wait_and_load(int *ptr, int placeholder)
+{
+	int futex_ret;
+	int value;
+
+retry:
+	futex_ret = syscall(__NR_futex, ptr, FUTEX_WAIT, placeholder, NULL,
+			    NULL, 0);
+	if (futex_ret == -1 && errno != EAGAIN) {
+		if (errno == EINTR)
+			goto retry;
+		perror("FUTEX_WAIT failed unexpectedly");
+		exit(EXIT_FAILURE);
+	}
+	value = __atomic_load_n(ptr, __ATOMIC_ACQUIRE);
+	if (value == placeholder)
+		goto retry;
+	return value;
+}
+
 TEST(kcmp)
 {
 	int ret;
@@ -4160,6 +4190,103 @@ TEST(user_notification_addfd_rlimit)
 	close(memfd);
 }
 
+TEST(user_notification_recv_dead)
+{
+	pid_t pid;
+	int status;
+	struct __clone_args args = {
+		.flags = CLONE_FILES,
+		.exit_signal = SIGCHLD,
+	};
+	struct seccomp_notif notif = {};
+	struct shared_data {
+		int notif_fd;
+	} *shared_data;
+
+	shared_data = mmap(NULL, sizeof(struct shared_data),
+			   PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_SHARED,
+			   -1, 0);
+	ASSERT_NE(NULL, shared_data);
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+		TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
+	}
+
+	pid = sys_clone3(&args, sizeof(args));
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		shared_data->notif_fd = user_notif_syscall(
+				__NR_mknodat, SECCOMP_FILTER_FLAG_NEW_LISTENER);
+		if (shared_data->notif_fd < 0)
+			_exit(EXIT_FAILURE);
+
+		_exit(EXIT_SUCCESS);
+	}
+
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(true, WIFEXITED(status));
+	EXPECT_EQ(0, WEXITSTATUS(status));
+
+	/* non-blocking recv */
+	EXPECT_EQ(-1, ioctl(shared_data->notif_fd, SECCOMP_IOCTL_NOTIF_RECV, &notif));
+	EXPECT_EQ(ENOTCONN, errno);
+
+	/* blocking recv */
+	set_blocking(shared_data->notif_fd);
+	EXPECT_EQ(-1, ioctl(shared_data->notif_fd, SECCOMP_IOCTL_NOTIF_RECV, &notif));
+	EXPECT_EQ(ENOTCONN, errno);
+}
+
+TEST(user_notification_recv_nonblock)
+{
+	pid_t pid;
+	struct __clone_args args = {
+		.flags = CLONE_FILES,
+		.exit_signal = SIGCHLD,
+	};
+	struct seccomp_notif notif = {};
+	struct shared_data {
+		int notif_fd;
+	} *shared_data;
+
+	shared_data = mmap(NULL, sizeof(struct shared_data),
+			   PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_SHARED,
+			   -1, 0);
+	ASSERT_NE(NULL, shared_data);
+	shared_data->notif_fd = -1;
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+		TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
+	}
+
+	pid = sys_clone3(&args, sizeof(args));
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		int fd;
+
+		fd = user_notif_syscall(__NR_mknodat,
+					SECCOMP_FILTER_FLAG_NEW_LISTENER);
+		if (fd < 0) {
+			store_and_wake(&shared_data->notif_fd, -2);
+			_exit(EXIT_FAILURE);
+		}
+		store_and_wake(&shared_data->notif_fd, fd);
+
+		while (1)
+			pause();
+	}
+
+	wait_and_load(&shared_data->notif_fd, -1);
+
+	/* non-blocking recv */
+	EXPECT_EQ(-1, ioctl(shared_data->notif_fd, SECCOMP_IOCTL_NOTIF_RECV,
+			    &notif));
+	EXPECT_EQ(ENOENT, errno);
+
+	kill(pid, SIGKILL);
+}
+
 /*
  * TODO:
  * - expand NNP testing
-- 
2.29.1.341.ge80a0c044ae-goog