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Subject[PATCH v7 2/2] selftests: add tests for pidfd_send_signal()
Date
As suggested by Andrew Morton in [1] add selftests for the new
sys_pidfd_send_signal() syscall:

/* test_pidfd_send_signal_syscall_support */
Test whether the pidfd_send_signal() syscall is supported and the tests can
be run or need to be skipped.

/* test_pidfd_send_signal_simple_success */
Test whether sending a signal via a pidfd works.

/* test_pidfd_send_signal_exited_fail */
Verify that sending a signal to an already exited process fails with ESRCH.

/* test_pidfd_send_signal_recycled_pid_fail */
Verify that a recycled pid cannot be signaled via a pidfd referring to an
already exited process that had the same pid (cf. [2], [3]).

[1]: https://lore.kernel.org/lkml/20181228152012.dbf0508c2508138efc5f2bbe@linux-foundation.org/
[2]: https://lore.kernel.org/lkml/20181230210245.GA30252@mail.hallyn.com/
[3]: https://lore.kernel.org/lkml/20181230232711.7aayb7vnhogbv4co@brauner.io/

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jann Horn <jannh@google.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Christian Brauner <christian@brauner.io>
Acked-by: Serge Hallyn <serge@hallyn.com>
---
/* Changelog */
v7:
- add test for pid recycling (cf. [2] and [3]) as suggested by Serge
- add test for pidfd_send_signal() syscalls support so we can skip tests if
it isn't
v6:
- patch introduced
v5..v0:
- patch not present
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/pidfd/Makefile | 6 +
tools/testing/selftests/pidfd/pidfd_test.c | 381 +++++++++++++++++++++
3 files changed, 388 insertions(+)
create mode 100644 tools/testing/selftests/pidfd/Makefile
create mode 100644 tools/testing/selftests/pidfd/pidfd_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index eb54df682d56..84dd78a684e4 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -29,6 +29,7 @@ TARGETS += net
TARGETS += netfilter
TARGETS += networking/timestamping
TARGETS += nsfs
+TARGETS += pidfd
TARGETS += powerpc
TARGETS += proc
TARGETS += pstore
diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
new file mode 100644
index 000000000000..deaf8073bc06
--- /dev/null
+++ b/tools/testing/selftests/pidfd/Makefile
@@ -0,0 +1,6 @@
+CFLAGS += -g -I../../../../usr/include/
+
+TEST_GEN_PROGS := pidfd_test
+
+include ../lib.mk
+
diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
new file mode 100644
index 000000000000..d59378a93782
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_test.c
@@ -0,0 +1,381 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/types.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/mount.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
+ unsigned int flags)
+{
+ return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
+}
+
+static int signal_received;
+
+static void set_signal_received_on_sigusr1(int sig)
+{
+ if (sig == SIGUSR1)
+ signal_received = 1;
+}
+
+/*
+ * Straightforward test to see whether pidfd_send_signal() works is to send
+ * a signal to ourself.
+ */
+static int test_pidfd_send_signal_simple_success(void)
+{
+ int pidfd, ret;
+ const char *test_name = "pidfd_send_signal send SIGUSR1";
+
+ pidfd = open("/proc/self", O_DIRECTORY | O_CLOEXEC);
+ if (pidfd < 0)
+ ksft_exit_fail_msg(
+ "%s test: Failed to open process file descriptor\n",
+ test_name);
+
+ signal(SIGUSR1, set_signal_received_on_sigusr1);
+
+ ret = sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0);
+ close(pidfd);
+ if (ret < 0)
+ ksft_exit_fail_msg("%s test: Failed to send signal\n",
+ test_name);
+
+ if (signal_received != 1)
+ ksft_exit_fail_msg("%s test: Failed to receive signal\n",
+ test_name);
+
+ signal_received = 0;
+ ksft_test_result_pass("%s test: Sent signal\n", test_name);
+ return 0;
+}
+
+static int wait_for_pid(pid_t pid)
+{
+ int status, ret;
+
+again:
+ ret = waitpid(pid, &status, 0);
+ if (ret == -1) {
+ if (errno == EINTR)
+ goto again;
+
+ return -1;
+ }
+
+ if (ret != pid)
+ goto again;
+
+ if (!WIFEXITED(status))
+ return -1;
+
+ return WEXITSTATUS(status);
+}
+
+static int test_pidfd_send_signal_exited_fail(void)
+{
+ int pidfd, ret, saved_errno;
+ char buf[256];
+ pid_t pid;
+ const char *test_name = "pidfd_send_signal signal exited process";
+
+ pid = fork();
+ if (pid < 0)
+ ksft_exit_fail_msg("%s test: Failed to create new process\n",
+ test_name);
+
+ if (pid == 0)
+ _exit(EXIT_SUCCESS);
+
+ snprintf(buf, sizeof(buf), "/proc/%d", pid);
+
+ pidfd = open(buf, O_DIRECTORY | O_CLOEXEC);
+
+ (void)wait_for_pid(pid);
+
+ if (pidfd < 0)
+ ksft_exit_fail_msg(
+ "%s test: Failed to open process file descriptor\n",
+ test_name);
+
+ ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
+ saved_errno = errno;
+ close(pidfd);
+ if (ret == 0)
+ ksft_exit_fail_msg(
+ "%s test: Managed to send signal to process even though it should have failed\n",
+ test_name);
+
+ if (saved_errno != ESRCH)
+ ksft_exit_fail_msg(
+ "%s test: Expected to receive ESRCH as errno value but received %d instead\n",
+ test_name, saved_errno);
+
+ ksft_test_result_pass("%s test: Failed to send signal as expected\n",
+ test_name);
+ return 0;
+}
+
+/*
+ * The kernel reserves 300 pids via RESERVED_PIDS in kernel/pid.c
+ * That means, when it wraps around any pid < 300 will be skipped.
+ * So we need to use a pid > 300 in order to test recycling.
+ */
+#define PID_RECYCLE 1000
+
+/*
+ * Maximum number of cycles we allow. This is equivalent to PID_MAX_DEFAULT.
+ * If users set a higher limit or we have cycled PIDFD_MAX_DEFAULT number of
+ * times then we skip the test to not go into an infinite loop or block for a
+ * long time.
+ */
+#define PIDFD_MAX_DEFAULT 0x8000
+
+/*
+ * Define a few custom error codes for the child process to clearly indicate
+ * what is happening. This way we can tell the difference between a system
+ * error, a test error, etc.
+ */
+#define PIDFD_PASS 0
+#define PIDFD_FAIL 1
+#define PIDFD_ERROR 2
+#define PIDFD_SKIP 3
+#define PIDFD_XFAIL 4
+
+static int test_pidfd_send_signal_recycled_pid_fail(void)
+{
+ int i, ret;
+ pid_t pid1;
+ const char *test_name = "pidfd_send_signal signal recycled pid";
+
+ ret = unshare(CLONE_NEWPID);
+ if (ret < 0)
+ ksft_exit_fail_msg("%s test: Failed to unshare pid namespace\n",
+ test_name);
+
+ ret = unshare(CLONE_NEWNS);
+ if (ret < 0)
+ ksft_exit_fail_msg(
+ "%s test: Failed to unshare mount namespace\n",
+ test_name);
+
+ ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
+ if (ret < 0)
+ ksft_exit_fail_msg("%s test: Failed to remount / private\n",
+ test_name);
+
+ /* pid 1 in new pid namespace */
+ pid1 = fork();
+ if (pid1 < 0)
+ ksft_exit_fail_msg("%s test: Failed to create new process\n",
+ test_name);
+
+ if (pid1 == 0) {
+ char buf[256];
+ pid_t pid2;
+ int pidfd = -1;
+
+ (void)umount2("/proc", MNT_DETACH);
+ ret = mount("proc", "/proc", "proc", 0, NULL);
+ if (ret < 0)
+ _exit(PIDFD_ERROR);
+
+ /* grab pid PID_RECYCLE */
+ for (i = 0; i <= PIDFD_MAX_DEFAULT; i++) {
+ pid2 = fork();
+ if (pid2 < 0)
+ _exit(PIDFD_ERROR);
+
+ if (pid2 == 0)
+ _exit(PIDFD_PASS);
+
+ if (pid2 == PID_RECYCLE) {
+ snprintf(buf, sizeof(buf), "/proc/%d", pid2);
+ ksft_print_msg("pid to recycle is %d\n", pid2);
+ pidfd = open(buf, O_DIRECTORY | O_CLOEXEC);
+ }
+
+ if (wait_for_pid(pid2))
+ _exit(PIDFD_ERROR);
+
+ if (pid2 >= PID_RECYCLE)
+ break;
+ }
+
+ /*
+ * We want to be as predictable as we can so if we haven't been
+ * able to grab pid PID_RECYCLE skip the test.
+ */
+ if (pid2 != PID_RECYCLE) {
+ /* skip test */
+ close(pidfd);
+ _exit(PIDFD_SKIP);
+ }
+
+ if (pidfd < 0)
+ _exit(PIDFD_ERROR);
+
+ for (i = 0; i <= PIDFD_MAX_DEFAULT; i++) {
+ char c;
+ int pipe_fds[2];
+ pid_t recycled_pid;
+ int child_ret = PIDFD_PASS;
+
+ ret = pipe2(pipe_fds, O_CLOEXEC);
+ if (ret < 0)
+ _exit(PIDFD_ERROR);
+
+ recycled_pid = fork();
+ if (recycled_pid < 0)
+ _exit(PIDFD_ERROR);
+
+ if (recycled_pid == 0) {
+ close(pipe_fds[1]);
+ (void)read(pipe_fds[0], &c, 1);
+ close(pipe_fds[0]);
+
+ _exit(PIDFD_PASS);
+ }
+
+ /*
+ * Stop the child so we can inspect whether we have
+ * recycled pid PID_RECYCLE.
+ */
+ close(pipe_fds[0]);
+ ret = kill(recycled_pid, SIGSTOP);
+ close(pipe_fds[1]);
+ if (ret) {
+ (void)wait_for_pid(recycled_pid);
+ _exit(PIDFD_ERROR);
+ }
+
+ /*
+ * We have recycled the pid. Try to signal it. This
+ * needs to fail since this is a different process than
+ * the one the pidfd refers to.
+ */
+ if (recycled_pid == PID_RECYCLE) {
+ ret = sys_pidfd_send_signal(pidfd, SIGCONT,
+ NULL, 0);
+ if (ret && errno == ESRCH)
+ child_ret = PIDFD_XFAIL;
+ else
+ child_ret = PIDFD_FAIL;
+ }
+
+ /* let the process move on */
+ ret = kill(recycled_pid, SIGCONT);
+ if (ret)
+ (void)kill(recycled_pid, SIGKILL);
+
+ if (wait_for_pid(recycled_pid))
+ _exit(PIDFD_ERROR);
+
+ switch (child_ret) {
+ case PIDFD_FAIL:
+ /* fallthrough */
+ case PIDFD_XFAIL:
+ _exit(child_ret);
+ case PIDFD_PASS:
+ break;
+ default:
+ /* not reached */
+ _exit(PIDFD_ERROR);
+ }
+
+ /*
+ * If the user set a custom pid_max limit we could be
+ * in the millions.
+ * Skip the test in this case.
+ */
+ if (recycled_pid > PIDFD_MAX_DEFAULT)
+ _exit(PIDFD_SKIP);
+ }
+
+ /* failed to recycle pid */
+ _exit(PIDFD_SKIP);
+ }
+
+ ret = wait_for_pid(pid1);
+ switch (ret) {
+ case PIDFD_FAIL:
+ ksft_exit_fail_msg(
+ "%s test: Managed to signal recycled pid %d\n",
+ test_name, PID_RECYCLE);
+ case PIDFD_PASS:
+ ksft_exit_fail_msg("%s test: Failed to recycle pid %d\n",
+ test_name, PID_RECYCLE);
+ case PIDFD_SKIP:
+ ksft_print_msg("%s test: Skipping test\n", test_name);
+ ret = 0;
+ break;
+ case PIDFD_XFAIL:
+ ksft_test_result_pass(
+ "%s test: Failed to signal recycled pid as expected\n",
+ test_name);
+ ret = 0;
+ break;
+ default /* PIDFD_ERROR */:
+ ksft_exit_fail_msg("%s test: Error while running tests\n",
+ test_name);
+ }
+
+ return ret;
+}
+
+static int test_pidfd_send_signal_syscall_support(void)
+{
+ int pidfd, ret;
+ const char *test_name = "pidfd_send_signal check for support";
+
+ pidfd = open("/proc/self", O_DIRECTORY | O_CLOEXEC);
+ if (pidfd < 0)
+ ksft_exit_fail_msg(
+ "%s test: Failed to open process file descriptor\n",
+ test_name);
+
+ ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
+ if (ret < 0) {
+ /*
+ * pidfd_send_signal() will currently return ENOSYS when
+ * CONFIG_PROC_FS is not set.
+ */
+ if (errno == ENOSYS)
+ ksft_exit_skip(
+ "%s test: pidfd_send_signal() syscall not supported (Ensure that CONFIG_PROC_FS=y is set)\n",
+ test_name);
+
+ ksft_exit_fail_msg("%s test: Failed to send signal\n",
+ test_name);
+ }
+
+ close(pidfd);
+ ksft_test_result_pass(
+ "%s test: pidfd_send_signal() syscall is supported. Tests can be executed\n",
+ test_name);
+ return 0;
+}
+
+int main(int argc, char **argv)
+{
+ ksft_print_header();
+
+ test_pidfd_send_signal_syscall_support();
+ test_pidfd_send_signal_simple_success();
+ test_pidfd_send_signal_exited_fail();
+ test_pidfd_send_signal_recycled_pid_fail();
+
+ return ksft_exit_pass();
+}
--
2.19.1
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