[PATCH v3 3/3] selftests: pidfd: add tests for PIDFD_SELF_*

Lorenzo Stoakes
2024-10-16T10:21:08Z

Add tests to assert that PIDFD_SELF_* correctly refers to the current
thread and process.

This is only practically meaningful to pidfd_send_signal() and
pidfd_getfd(), but also explicitly test that we disallow this feature for
setns() where it would make no sense.

We cannot reasonably wait on ourself using waitid(P_PIDFD, ...) so while in
theory PIDFD_SELF_* would work here, we'd be left blocked if we tried it.

We defer testing of mm-specific functionality which uses pidfd, namely
process_madvise() and process_mrelease() to mm testing (though note the
latter can not be sensibly tested as it would require the testing process
to be dying).

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/testing/selftests/pidfd/pidfd.h | 8 +
.../selftests/pidfd/pidfd_getfd_test.c | 141 ++++++++++++++++++
.../selftests/pidfd/pidfd_setns_test.c | 11 ++
tools/testing/selftests/pidfd/pidfd_test.c | 76 ++++++++--
4 files changed, 224 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 88d6830ee004..1640b711889b 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -50,6 +50,14 @@
#define PIDFD_NONBLOCK O_NONBLOCK
#endif

+/* System header file may not have this available. */
+#ifndef PIDFD_SELF_THREAD
+#define PIDFD_SELF_THREAD -100
+#endif
+#ifndef PIDFD_SELF_THREAD_GROUP
+#define PIDFD_SELF_THREAD_GROUP -200
+#endif
+
/*
* The kernel reserves 300 pids via RESERVED_PIDS in kernel/pid.c
* That means, when it wraps around any pid < 300 will be skipped.
diff --git a/tools/testing/selftests/pidfd/pidfd_getfd_test.c b/tools/testing/selftests/pidfd/pidfd_getfd_test.c
index cd51d547b751..48d224b13c01 100644
--- a/tools/testing/selftests/pidfd/pidfd_getfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_getfd_test.c
@@ -6,6 +6,7 @@
#include <limits.h>
#include <linux/types.h>
#include <poll.h>
+#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
@@ -15,6 +16,7 @@
#include <sys/prctl.h>
#include <sys/wait.h>
#include <unistd.h>
+#include <sys/mman.h>
#include <sys/socket.h>
#include <linux/kcmp.h>

@@ -114,6 +116,94 @@ static int child(int sk)
return ret;
}

+static int __pidfd_self_thread_worker(unsigned long page_size)
+{
+ int memfd;
+ int newfd;
+ char *ptr;
+ int err = 0;
+
+ /*
+ * Unshare our FDs so we have our own set. This means
+ * PIDFD_SELF_THREAD_GROUP will fal.
+ */
+ if (unshare(CLONE_FILES) < 0) {
+ err = -errno;
+ goto exit;
+ }
+
+ /* Truncate, map in and write to our memfd. */
+ memfd = sys_memfd_create("test_self_child", 0);
+ if (memfd < 0) {
+ err = -errno;
+ goto exit;
+ }
+
+ if (ftruncate(memfd, page_size)) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, memfd, 0);
+ if (ptr == MAP_FAILED) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+ ptr[0] = 'y';
+ if (munmap(ptr, page_size)) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+
+ /* Get a thread-local duplicate of our memfd. */
+ newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD, memfd, 0);
+ if (newfd < 0) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+
+ if (memfd == newfd) {
+ err = -EINVAL;
+ goto exit_close_fds;
+ }
+
+ /* Map in new fd and make sure that the data is as expected. */
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, newfd, 0);
+ if (ptr == MAP_FAILED) {
+ err = -errno;
+ goto exit_close_fds;
+ }
+
+ if (ptr[0] != 'y') {
+ err = -EINVAL;
+ goto exit_close_fds;
+ }
+
+ if (munmap(ptr, page_size)) {
+ err = -errno;
+ goto exit_close_fds;
+ }
+
+exit_close_fds:
+ close(newfd);
+exit_close_memfd:
+ close(memfd);
+exit:
+ return err;
+}
+
+static void *pidfd_self_thread_worker(void *arg)
+{
+ unsigned long page_size = (unsigned long)arg;
+ int ret;
+
+ /* We forward any errors for the caller to handle. */
+ ret = __pidfd_self_thread_worker(page_size);
+ return (void *)(intptr_t)ret;
+}
+
FIXTURE(child)
{
/*
@@ -264,6 +354,57 @@ TEST_F(child, no_strange_EBADF)
EXPECT_EQ(errno, ESRCH);
}

+TEST(pidfd_self)
+{
+ int memfd = sys_memfd_create("test_self", 0);
+ unsigned long page_size = sysconf(_SC_PAGESIZE);
+ int newfd;
+ char *ptr;
+ pthread_t thread;
+ void *res;
+ int err;
+
+ ASSERT_GE(memfd, 0);
+ ASSERT_EQ(ftruncate(memfd, page_size), 0);
+
+ /*
+ * Map so we can assert that the duplicated fd references the same
+ * memory.
+ */
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, memfd, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+ ptr[0] = 'x';
+ ASSERT_EQ(munmap(ptr, page_size), 0);
+
+ /* Now get a duplicate of our memfd. */
+ newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD_GROUP, memfd, 0);
+ ASSERT_GE(newfd, 0);
+ ASSERT_NE(memfd, newfd);
+
+ /* Now map duplicate fd and make sure it references the same memory. */
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, newfd, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+ ASSERT_EQ(ptr[0], 'x');
+ ASSERT_EQ(munmap(ptr, page_size), 0);
+
+ /* Cleanup. */
+ close(memfd);
+ close(newfd);
+
+ /*
+ * Fire up the thread and assert that we can lookup the thread-specific
+ * PIDFD_SELF_THREAD (also aliased by PIDFD_SELF).
+ */
+ ASSERT_EQ(pthread_create(&thread, NULL, pidfd_self_thread_worker,
+ (void *)page_size), 0);
+ ASSERT_EQ(pthread_join(thread, &res), 0);
+ err = (int)(intptr_t)res;
+
+ ASSERT_EQ(err, 0);
+}
+
#if __NR_pidfd_getfd == -1
int main(void)
{
diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
index 7c2a4349170a..bbd39dc5ceb7 100644
--- a/tools/testing/selftests/pidfd/pidfd_setns_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
@@ -752,4 +752,15 @@ TEST(setns_einval)
close(fd);
}

+TEST(setns_pidfd_self_disallowed)
+{
+ ASSERT_EQ(setns(PIDFD_SELF_THREAD, 0), -1);
+ EXPECT_EQ(errno, EBADF);
+
+ errno = 0;
+
+ ASSERT_EQ(setns(PIDFD_SELF_THREAD_GROUP, 0), -1);
+ EXPECT_EQ(errno, EBADF);
+}
+
TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
index 9faa686f90e4..440447cf89ba 100644
--- a/tools/testing/selftests/pidfd/pidfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_test.c
@@ -42,12 +42,41 @@ static pid_t pidfd_clone(int flags, int *pidfd, int (*fn)(void *))
#endif
}

-static int signal_received;
+static pthread_t signal_received;

static void set_signal_received_on_sigusr1(int sig)
{
if (sig == SIGUSR1)
- signal_received = 1;
+ signal_received = pthread_self();
+}
+
+static int send_signal(int pidfd)
+{
+ int ret = 0;
+
+ if (sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0) < 0) {
+ ret = -EINVAL;
+ goto exit;
+ }
+
+ if (signal_received != pthread_self()) {
+ ret = -EINVAL;
+ goto exit;
+ }
+
+exit:
+ signal_received = 0;
+ return ret;
+}
+
+static void *send_signal_worker(void *arg)
+{
+ int pidfd = (int)(intptr_t)arg;
+ int ret;
+
+ /* We forward any errors for the caller to handle. */
+ ret = send_signal(pidfd);
+ return (void *)(intptr_t)ret;
}

/*
@@ -56,8 +85,11 @@ static void set_signal_received_on_sigusr1(int sig)
*/
static int test_pidfd_send_signal_simple_success(void)
{
- int pidfd, ret;
+ int pidfd;
const char *test_name = "pidfd_send_signal send SIGUSR1";
+ pthread_t thread;
+ void *thread_res;
+ int err;

if (!have_pidfd_send_signal) {
ksft_test_result_skip(
@@ -66,25 +98,45 @@ static int test_pidfd_send_signal_simple_success(void)
return 0;
}

+ signal(SIGUSR1, set_signal_received_on_sigusr1);
+
+ /* Try sending a signal to ourselves via /proc/self. */
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);
+ err = send_signal(pidfd);
+ if (err)
+ ksft_exit_fail_msg(
+ "%s test: Error %d on sending pidfd signal\n",
+ test_name, err);
+ close(pidfd);

- signal(SIGUSR1, set_signal_received_on_sigusr1);
+ /* Now try the same thing only using PIDFD_SELF_THREAD_GROUP. */
+ err = send_signal(PIDFD_SELF_THREAD_GROUP);
+ if (err)
+ ksft_exit_fail_msg(
+ "%s test: Error %d on PIDFD_SELF_THREAD_GROUP signal\n",
+ test_name, err);

- 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",
+ /*
+ * Now try the same thing in a thread and assert thread ID is equal to
+ * worker thread ID.
+ */
+ if (pthread_create(&thread, NULL, send_signal_worker,
+ (void *)(intptr_t)PIDFD_SELF_THREAD))
+ ksft_exit_fail_msg("%s test: Failed to create thread\n",
test_name);
-
- if (signal_received != 1)
- ksft_exit_fail_msg("%s test: Failed to receive signal\n",
+ if (pthread_join(thread, &thread_res))
+ ksft_exit_fail_msg("%s test: Failed to join thread\n",
test_name);
+ err = (int)(intptr_t)thread_res;
+ if (err)
+ ksft_exit_fail_msg(
+ "%s test: Error %d on PIDFD_SELF_THREAD signal\n",
+ test_name, err);

- signal_received = 0;
ksft_test_result_pass("%s test: Sent signal\n", test_name);
return 0;
}
--
2.46.2