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

[Shuah Khan <skhan@linuxfoundation.org>]

On 10/10/24 12:15, Lorenzo Stoakes wrote:
> 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        | 136 ++++++++++++++++++
>   .../selftests/pidfd/pidfd_setns_test.c        |  11 ++
>   tools/testing/selftests/pidfd/pidfd_test.c    |  67 +++++++--
>   4 files changed, 213 insertions(+), 9 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
> +

Can't we pick these up from linux/pidfd.h - patch 2/3 adds
them.

>   /*
>    * 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..10793fc845ed 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 +116,89 @@ static int child(int sk)
>   	return ret;
>   }
>   
> +static int __pidfd_self_thread_worker(unsigned long page_size)
> +{
> +	int memfd;
> +	int newfd;
> +	char *ptr;
> +	int ret = 0;
> +
> +	/*
> +	 * Unshare our FDs so we have our own set. This means
> +	 * PIDFD_SELF_THREAD_GROUP will fail.
> +	 */
> +	if (unshare(CLONE_FILES) < 0) {
> +		ret = -errno;
> +		goto exit;
> +	}
> +
> +	/* Truncate, map in and write to our memfd. */
> +	memfd = sys_memfd_create("test_self_child", 0);

Missing eror check.

> +	if (ftruncate(memfd, page_size)) {
> +		ret = -errno;
> +		goto exit;

Hmm. you probably need scoped cleanup paths. "exit" closes
memfd and newfd which isn't open yet and sys_memfd_create()
could fail and memfd doesn't need closing?

> +	}
> +
> +	ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
> +		   MAP_SHARED, memfd, 0);
> +	if (ptr == MAP_FAILED) {
> +		ret = -errno;
> +		goto exit;
> +	}
> +	ptr[0] = 'y';
> +	if (munmap(ptr, page_size)) {
> +		ret = -errno;
> +		goto exit;
> +	}
> +
> +	/* Get a thread-local duplicate of our memfd. */
> +	newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD, memfd, 0);
> +	if (newfd < 0) {
> +		ret = -errno;
> +		goto exit;

Same comment here - "exit" closes newfd

> +	}
> +
> +	if (memfd == newfd) {
> +		ret = -EINVAL;
> +		goto exit;
> +	}
> +
> +	/* 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) {
> +		ret = -errno;
> +		goto exit;
> +	}
> +
> +	if (ptr[0] != 'y') {
> +		ret = -EINVAL;
> +		goto exit;
> +	}
> +
> +	if (munmap(ptr, page_size)) {
> +		ret = -errno;
> +		goto exit;
> +	}
> +
> +exit:
> +	/* Cleanup. */
> +	close(newfd);
> +	close(memfd);
> +
> +	return ret;
> +}
> +
> +static void *pidfd_self_thread_worker(void *arg)
> +{
> +	unsigned long page_size = (unsigned long)arg;
> +	int ret;
> +
> +	ret = __pidfd_self_thread_worker(page_size);

Don't you want to check error here?

> +
> +	return (void *)(intptr_t)ret;
> +}
> +
>   FIXTURE(child)
>   {
>   	/*
> @@ -264,6 +349,57 @@ 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..ab5caa0368a1 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;
> +
> +	ret = send_signal(pidfd);
> +

Same here - don't you have to check ret?

> +	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 res;
>   
>   	if (!have_pidfd_send_signal) {
>   		ksft_test_result_skip(
> @@ -74,17 +106,34 @@ static int test_pidfd_send_signal_simple_success(void)
>   
>   	signal(SIGUSR1, set_signal_received_on_sigusr1);
>   
> -	ret = sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0);
> +	send_signal(pidfd);
>   	close(pidfd);
> -	if (ret < 0)
> -		ksft_exit_fail_msg("%s test: Failed to send signal\n",
> +
> +	/* Now try the same thing only using PIDFD_SELF_THREAD_GROUP. */
> +	res = send_signal(PIDFD_SELF_THREAD_GROUP);
> +	if (res)
> +		ksft_exit_fail_msg(
> +			"%s test: Error %d on PIDFD_SELF_THREAD_GROUP signal\n",
> +			test_name, res);
> +
> +	/*
> +	 * 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);
> +	res = (int)(intptr_t)thread_res;
> +	if (res)
> +		ksft_exit_fail_msg(
> +			"%s test: Error %d on PIDFD_SELF_THREAD signal\n",
> +			test_name, res);
>   
> -	signal_received = 0;
>   	ksft_test_result_pass("%s test: Sent signal\n", test_name);
>   	return 0;
>   }

thanks,
-- Shuah