Fix clone (CLONE_VM) pid/tid reset (BZ#19957)

As discussed in libc-alpha [1] current clone with CLONE_VM (without
CLONE_THREAD set) will reset the pthread pid/tid fields to -1.  The
issue is since memory is shared between the parent and child it will
clobber parent's cached pid/tid leading to internal inconsistencies
if the value is not restored.

And even it is restored it may lead to racy conditions when between
set/restore a thread might invoke pthread function that validate the
pthread with INVALID_TD_P/INVALID_NOT_TERMINATED_TD_P and thus get
wrong results.

As stated in BZ19957, previously reports of this behaviour was close
with EWONTFIX due the fact usage of clone outside glibc is tricky
since glibc requires consistent internal pthread, while using clone
directly may not provide it. However since now posix_spawn uses
clone (CLONE_VM) to fixes various issues related to previous vfork
usage this issue requires fixing.

The vfork implementation also does something similar, but instead
it negates and restores only the *pid* field and functions that
might access its value know to handle such case (getpid, raise
and pthread ones that uses INVALID_TD_P/INVALID_NOT_TERMINATED_TD_P
macros that check only *tid* field).  Also vfork does not call
__clone directly, instead calling either __NR_vfork or __NR_clone
directly.

So this patch removes this clone behavior by avoiding setting
the pthread pid/tid field for CLONE_VM. There is no need to
check for CLONE_THREAD, since the minimum supported kernel in all
architecture implies that CLONE_VM must be used with CLONE_THREAD,
otherwise clone returns EINVAL.

Instead of current approach of:

   int clone(int (*fn)(void *), void *child_stack, int flags, ...)
      [...]
      if (flags & CLONE_THREAD)
        goto do_syscall;
      pid_t new_value;
      if (flags & CLONE_VM)
        new_value = -1;
      else
        new_value = getpid ();
      THREAD_SETMEM (THREAD_SELF, pid, new_value);
      THREAD_SETMEM (THREAD_SELF, tid, new_value);

    do_syscall:
      [...]

The new approach uses:

   int clone(int (*fn)(void *), void *child_stack, int flags, ...)
      [...]
      if (flags & CLONE_VM)
        goto do_syscall;
      pid_t new_value = getpid ();
      THREAD_SETMEM (THREAD_SELF, pid, new_value);
      THREAD_SETMEM (THREAD_SELF, tid, new_value);

    do_syscall:
      [...]

It also removes the linux tst-getpid2.c test which expects the previous
behavior and instead add another clone test.

Tested on x86_64, i686, x32, powerpc64le, aarch64, armhf, s390, and
s390x. I also did limited check on mips32 and sparc64 (using the new
added test).

I also got reviews from both m68k, hppa, and tile.  So I presume for
these architecture the patch works.

The fixes for alpha, microblaze, sh, ia64, and nio2 have not been
tested.

[1] https://sourceware.org/ml/libc-alpha/2016-04/msg00307.html

	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == nptl] (test): Remove
	tst-getpid2.
	(test): Add tst-clone2.
	* sysdeps/unix/sysv/linux/tst-clone2.c: New file.
	* sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Do not change
	pid/tid fields for CLONE_VM.
	* sysdeps/unix/sysv/linux/arm/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/i386/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/mips/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/tst-getpid2.c: Remove file.

1 files changed, 178 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/tst-clone2.c b/sysdeps/unix/sysv/linux/tst-clone2.c
new file mode 100644
index 0000000000..68a7e6d6e2
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-clone2.c
@@ -0,0 +1,178 @@
+/* Test if CLONE_VM does not change pthread pid/tid field (BZ #19957)
+   Copyright (C) 2016 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sched.h>
+#include <signal.h>
+#include <string.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <tls.h> /* for THREAD_* macros.  */
+
+static int sig;
+static int pipefd[2];
+
+static int
+f (void *a)
+{
+  close (pipefd[0]);
+
+  pid_t pid = THREAD_GETMEM (THREAD_SELF, pid);
+  pid_t tid = THREAD_GETMEM (THREAD_SELF, tid);
+
+  while (write (pipefd[1], &pid, sizeof pid) < 0)
+    continue;
+  while (write (pipefd[1], &tid, sizeof tid) < 0)
+    continue;
+
+  return 0;
+}
+
+
+static int
+clone_test (int clone_flags)
+{
+  sig = SIGRTMIN;
+  sigset_t ss;
+  sigemptyset (&ss);
+  sigaddset (&ss, sig);
+  if (sigprocmask (SIG_BLOCK, &ss, NULL) != 0)
+    {
+      printf ("sigprocmask failed: %m\n");
+      return 1;
+    }
+
+  if (pipe2 (pipefd, O_CLOEXEC))
+    {
+      printf ("sigprocmask failed: %m\n");
+      return 1;
+    }
+
+  pid_t ppid = getpid ();
+
+#ifdef __ia64__
+  extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base,
+		       size_t __child_stack_size, int __flags,
+		       void *__arg, ...);
+  char st[256 * 1024] __attribute__ ((aligned));
+  pid_t p = __clone2 (f, st, sizeof (st), clone_flags, 0);
+#else
+  char st[128 * 1024] __attribute__ ((aligned));
+#if _STACK_GROWS_DOWN
+  pid_t p = clone (f, st + sizeof (st), clone_flags, 0);
+#elif _STACK_GROWS_UP
+  pid_t p = clone (f, st, clone_flags, 0);
+#else
+#error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
+#endif
+#endif
+  close (pipefd[1]);
+
+  if (p == -1)
+    {
+      printf ("clone failed: %m\n");
+      return 1;
+    }
+
+  pid_t pid, tid;
+  if (read (pipefd[0], &pid, sizeof pid) != sizeof pid)
+    {
+      printf ("read pid failed: %m\n");
+      kill (p, SIGKILL);
+      return 1;
+    }
+  if (read (pipefd[0], &tid, sizeof tid) != sizeof tid)
+    {
+      printf ("read pid failed: %m\n");
+      kill (p, SIGKILL);
+      return 1;
+    }
+
+  close (pipefd[0]);
+
+  int ret = 0;
+
+  /* For CLONE_VM glibc clone implementation does not change the pthread
+     pid/tid field.  */
+  if ((clone_flags & CLONE_VM) == CLONE_VM)
+    {
+      if ((ppid != pid) || (ppid != tid))
+	{
+	  printf ("parent pid (%i) != received pid/tid (%i/%i)\n",
+		  (int)ppid, (int)pid, (int)tid);
+	  ret = 1;
+	}
+    }
+  /* For any other flag clone updates the new pthread pid and tid with
+     the clone return value.  */
+  else
+    {
+      if ((p != pid) || (p != tid))
+	{
+	  printf ("child pid (%i) != received pid/tid (%i/%i)\n",
+		  (int)p, (int)pid, (int)tid);
+	  ret = 1;
+	}
+    }
+
+  int e;
+  if (waitpid (p, &e, __WCLONE) != p)
+    {
+      puts ("waitpid failed");
+      kill (p, SIGKILL);
+      return 1;
+    }
+  if (!WIFEXITED (e))
+    {
+      if (WIFSIGNALED (e))
+	printf ("died from signal %s\n", strsignal (WTERMSIG (e)));
+      else
+	puts ("did not terminate correctly");
+      return 1;
+    }
+  if (WEXITSTATUS (e) != 0)
+    {
+      printf ("exit code %d\n", WEXITSTATUS (e));
+      return 1;
+    }
+
+  return ret;
+}
+
+int
+do_test (void)
+{
+  /* First, check that the clone implementation, without any flag, updates
+     the struct pthread to contain the new PID and TID.  */
+  int ret = clone_test (0);
+  /* Second, check that with CLONE_VM the struct pthread PID and TID fields
+     remain unmodified after the clone.  Any modifications would cause problem
+     for the parent as described in bug 19957.  */
+  ret += clone_test (CLONE_VM);
+  return ret;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"