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Date:   Tue, 1 Jan 2019 16:07:44 +0100
From:   Christian Brauner <christian@brauner.io>
To:     "Serge E. Hallyn" <serge@hallyn.com>
Cc:     linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        luto@kernel.org, arnd@arndb.de, keescook@chromium.org,
        akpm@linux-foundation.org, jannh@google.com, oleg@redhat.com,
        cyphar@cyphar.com, viro@zeniv.linux.org.uk,
        linux-fsdevel@vger.kernel.org, dancol@google.com,
        timmurray@google.com, fweimer@redhat.com, tglx@linutronix.de,
        x86@kernel.org, ebiederm@xmission.com
Subject: Re: [PATCH v6 2/2] selftests: add tests for pidfd_send_signal()
Message-ID: <20190101150743.ikrrfcogqec2oqeh@brauner.io>
References: <20181229222756.30027-1-christian@brauner.io>
 <20181229222756.30027-2-christian@brauner.io>
 <20181230210245.GA30252@mail.hallyn.com>
 <20181230232711.7aayb7vnhogbv4co@brauner.io>
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On Mon, Dec 31, 2018 at 12:27:13AM +0100, Christian Brauner wrote:
> On Sun, Dec 30, 2018 at 03:02:45PM -0600, Serge Hallyn wrote:
> > On Sat, Dec 29, 2018 at 11:27:56PM +0100, Christian Brauner wrote:
> > > As suggested by Andrew Morton in [1] add selftests for the new
> > > sys_pidfd_send_signal() syscall.
> > > This tests whether we can send a signal to an existing process and whether
> > > sending a signal to a process that has already exited fails with ESRCH.
> > > 
> > > [1]: https://lore.kernel.org/lkml/20181228152012.dbf0508c2508138efc5f2bbe@linux-foundation.org/
> > > 
> > > Cc: Arnd Bergmann <arnd@arndb.de>
> > > Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> > > Cc: Kees Cook <keescook@chromium.org>
> > > Cc: Serge Hallyn <serge@hallyn.com>
> > 
> > Acked-by: Serge Hallyn <serge@hallyn.com>
> > 
> > Not saying you need to do this, but it would be neat if you could test
> > sending to a pid which has been recycled :)
> 
> Yeah, I thought about it but it's a little weird code. First of all, we
> can't set /proc/sys/kernel/pid_max to a very low value since this is a
> system wide setting. So we need to recycle a lot via fork(). Something
> along the lines of:
> - unshare pid namespace
> - fork to create pid 1 in new pid namespace
> - cycle with fork() until pid > 300 since pids lower than 300 are
>   reserved by the kernel.
>   (That means if we simply use the first fork() after we created pid 1 we
>   would never be able to recycle the pid since we skip over it. :))
> - get pidfd to the pid > 300 we just created
> - wait on the pid > 300
> - cycle via fork() until we have reached the same pid > 300 again
> - send SIGSTOP to that recycled process
> - test that we cannot send SIGCONT to this SIGSTOPed task via the pidfd we
>   received before
> - send SIGCONT to the SIGSTOPed recycled pid and exit

Ok, I have something like this in my tree now that tests for pid
recycling. I'm going to send it out tomorrow since I reckon Andrew and
others will be off today.
But fwiw it sits in https://github.com/brauner/linux/commits/2018-12-02/procfds

> 
> Christian
> 
> > 
> > > 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>
> > > ---
> > > /* Changelog */
> > > 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 | 130 +++++++++++++++++++++
> > >  3 files changed, 137 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 24b9934fb269..63b0d8a0ebf7 100644
> > > --- a/tools/testing/selftests/Makefile
> > > +++ b/tools/testing/selftests/Makefile
> > > @@ -27,6 +27,7 @@ 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..edcd59979b10
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/pidfd/pidfd_test.c
> > > @@ -0,0 +1,130 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +#define _GNU_SOURCE
> > > +#include <errno.h>
> > > +#include <fcntl.h>
> > > +#include <linux/types.h>
> > > +#include <signal.h>
> > > +#include <stdio.h>
> > > +#include <stdlib.h>
> > > +#include <string.h>
> > > +#include <syscall.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 do_exit_success(int sig)
> > > +{
> > > +	signal_received = 1;
> > > +}
> > > +
> > > +/*
> > > + * Straightforward test to see whether pidfd_send_signal() works is to send
> > > + * a signal to ourselves.
> > > + */
> > > +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, do_exit_success);
> > > +
> > > +	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 void wait_for_pid(pid_t pid)
> > > +{
> > > +	int status, ret;
> > > +
> > > +again:
> > > +	ret = waitpid(pid, &status, 0);
> > > +	if (ret == -1) {
> > > +		if (errno == EINTR)
> > > +			goto again;
> > > +
> > > +		return;
> > > +	}
> > > +
> > > +	if (ret != pid)
> > > +		goto again;
> > > +}
> > > +
> > > +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);
> > > +
> > > +	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;
> > > +}
> > > +
> > > +int main(int argc, char **argv)
> > > +{
> > > +	ksft_print_header();
> > > +
> > > +	test_pidfd_send_signal_simple_success();
> > > +	test_pidfd_send_signal_exited_fail();
> > > +
> > > +	return ksft_exit_pass();
> > > +}
> > > -- 
> > > 2.19.1