linux: Add tst-pidfd.c

To check for the pidfd functions pidfd_open, pidfd_getfd, pid_send_signal,
and waitid with P_PIDFD.

Checked on x86_64-linux-gnu and i686-linux-gnu.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/unix/sysv/linux/Makefile

@@ -128,6 +128,7 @@ tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
   tst-scm_rights \
   tst-epoll \
   tst-getauxval \
+  tst-pidfd \
   # tests
 
 # For +depfiles in Makerules.

sysdeps/unix/sysv/linux/tst-pidfd.c

@@ -0,0 +1,172 @@
+/* Basic tests for Linux pidfd interfaces.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <support/process_state.h>
+#include <support/support.h>
+#include <support/xsignal.h>
+#include <support/xunistd.h>
+#include <support/xsocket.h>
+#include <sys/pidfd.h>
+#include <sys/wait.h>
+
+#define REMOTE_PATH "/dev/null"
+
+/* The pair of sockets used for coordination.  The subprocess uses
+   sockets[1].  */
+static int sockets[2];
+
+static pid_t ppid;
+static uid_t puid;
+
+static void
+sighandler (int sig)
+{
+}
+
+static void
+subprocess (void)
+{
+  xsignal (SIGUSR1, sighandler);
+  xsignal (SIGUSR2, sighandler);
+
+  /* Check first pidfd_send_signal with default NULL siginfo_t argument.  */
+  {
+    sigset_t set;
+    sigemptyset (&set);
+    sigaddset (&set, SIGUSR1);
+    siginfo_t info;
+    TEST_COMPARE (sigtimedwait (&set, &info, NULL), SIGUSR1);
+    TEST_COMPARE (info.si_signo, SIGUSR1);
+    TEST_COMPARE (info.si_errno, 0);
+    TEST_COMPARE (info.si_code, SI_USER);
+    TEST_COMPARE (info.si_pid, ppid);
+    TEST_COMPARE (info.si_uid, puid);
+  }
+
+  /* Check second pidfd_send_signal with crafted siginfo_t argument.  */
+  {
+    sigset_t set;
+    sigemptyset (&set);
+    sigaddset (&set, SIGUSR2);
+    siginfo_t info;
+    TEST_COMPARE (sigtimedwait (&set, &info, NULL), SIGUSR2);
+    TEST_COMPARE (info.si_signo, SIGUSR2);
+    TEST_COMPARE (info.si_errno, EAGAIN);
+    TEST_COMPARE (info.si_code, -10);
+    TEST_COMPARE (info.si_pid, ppid);
+    TEST_COMPARE (info.si_uid, puid);
+  }
+
+  /* Send a local file descriptor value to check pidfd_getfd.  */
+  int remote_fd = xopen (REMOTE_PATH, O_WRONLY | O_CLOEXEC, 0);
+  xsendto (sockets[1], &remote_fd, sizeof (remote_fd), 0, NULL, 0);
+
+  /* Wait for final pidfd_send_signal.  */
+  pause ();
+
+  _exit (0);
+}
+
+static int
+do_test (void)
+{
+  {
+    /* The pidfd_getfd syscall was the last in the set of pidfd related
+       syscalls added to the kernel.  Use pidfd_getfd to decide if this
+       kernel has pidfd support that we can test.  */
+    int r = pidfd_getfd (0, 0, 1);
+    TEST_VERIFY_EXIT (r == -1);
+    if (errno == ENOSYS)
+      FAIL_UNSUPPORTED ("kernel does not support pidfd_getfd, skipping test");
+  }
+
+  ppid = getpid ();
+  puid = getuid ();
+
+  TEST_COMPARE (socketpair (AF_UNIX, SOCK_STREAM, 0, sockets), 0);
+
+  pid_t pid = xfork ();
+  if (pid == 0)
+    {
+      xclose (sockets[0]);
+      subprocess ();
+    }
+  xclose (sockets[1]);
+
+  TEST_COMPARE (pidfd_open (-1, 0), -1);
+  TEST_COMPARE (errno, EINVAL);
+
+  int pidfd = pidfd_open (pid, 0);
+  TEST_VERIFY (pidfd != -1);
+
+  /* Wait for first sigtimedwait.  */
+  support_process_state_wait (pid, support_process_state_sleeping);
+  TEST_COMPARE (pidfd_send_signal (pidfd, SIGUSR1, NULL, 0), 0);
+
+  /* Wait for second sigtimedwait.  */
+  support_process_state_wait (pid, support_process_state_sleeping);
+  {
+    siginfo_t info =
+      {
+	.si_signo = SIGUSR2,
+	.si_errno = EAGAIN,
+	.si_code = -10,
+	.si_pid = ppid,
+	.si_uid = puid
+      };
+    TEST_COMPARE (pidfd_send_signal (pidfd, SIGUSR2, &info, 0), 0);
+  }
+
+  /* Get remote file descriptor to check for pidfd_getfd.  */
+  {
+    int remote_fd;
+    xrecvfrom (sockets[0], &remote_fd, sizeof (remote_fd), 0, NULL, 0);
+
+    int fd = pidfd_getfd (pidfd, remote_fd, 0);
+    TEST_VERIFY (fd > 0);
+
+    char *path = xasprintf ("/proc/%d/fd/%d", pid, remote_fd);
+    char *resolved = xreadlink (path);
+    TEST_COMPARE_STRING (resolved, REMOTE_PATH);
+
+    int remote_fd_mode = fcntl (fd, F_GETFL);
+    TEST_VERIFY (remote_fd_mode != -1);
+    TEST_VERIFY (remote_fd_mode & O_WRONLY);
+
+    int remote_fd_flags = fcntl (fd, F_GETFD);
+    TEST_VERIFY (remote_fd_flags != -1);
+    TEST_VERIFY (remote_fd_flags & FD_CLOEXEC);
+  }
+
+  TEST_COMPARE (pidfd_send_signal (pidfd, SIGKILL, NULL, 0), 0);
+  {
+    siginfo_t info;
+    int r = waitid (P_PIDFD, pidfd, &info, WEXITED);
+    TEST_COMPARE (r, 0);
+    TEST_COMPARE (info.si_status, SIGKILL);
+    TEST_COMPARE (info.si_code, CLD_KILLED);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>