Re: [PATCH v3] debug: test for more required cacellation points (BZ# 29274)

[Carlos O'Donell <carlos@redhat.com>]

On 7/18/22 12:46, Adhemerval Zanella wrote:
> Generalize the test for cancellation point in __read_chk to also test
> the other fortified functions with required cancellation points.
> 
> Since there is not easy way to force some syscalls to block (for
> instance pread) the test tests two modes: cancellation on blocked
> syscalls and early cancellation on pending request.
> 
> Checked on aarch64-linux-gnu.

One issue left.
 
> Co-authored-by: Andreas Schwab <schwab@suse.de>
> ---
>  debug/Makefile              |   6 +-
>  debug/tst-chk-cancel.c      | 269 ++++++++++++++++++++++++++++++++++++
>  debug/tst-read-chk-cancel.c |  50 -------
>  3 files changed, 272 insertions(+), 53 deletions(-)
>  create mode 100644 debug/tst-chk-cancel.c
>  delete mode 100644 debug/tst-read-chk-cancel.c
> 
> diff --git a/debug/Makefile b/debug/Makefile
> index 456b349c4d..99cdf3221b 100644
> --- a/debug/Makefile
> +++ b/debug/Makefile
> @@ -110,7 +110,7 @@ CPPFLAGS-tst-longjmp_chk2.c += -D_FORTIFY_SOURCE=1
>  CFLAGS-tst-longjmp_chk3.c += -fexceptions -fasynchronous-unwind-tables
>  CPPFLAGS-tst-longjmp_chk3.c += -D_FORTIFY_SOURCE=1
>  CPPFLAGS-tst-realpath-chk.c += -D_FORTIFY_SOURCE=2
> -CPPFLAGS-tst-read-chk-cancel.c += -D_FORTIFY_SOURCE=2
> +CPPFLAGS-tst-chk-cancel.c += -D_FORTIFY_SOURCE=2
>  
>  # _FORTIFY_SOURCE tests.
>  # Auto-generate tests for _FORTIFY_SOURCE for different levels, compilers and
> @@ -206,7 +206,7 @@ tests += tst-ssp-1
>  endif
>  
>  ifeq ($(have-thread-library), yes)
> -tests += tst-read-chk-cancel
> +tests += tst-chk-cancel
>  endif
>  
>  ifeq (,$(CXX))
> @@ -248,4 +248,4 @@ $(objpfx)xtrace: xtrace.sh
>  	    -e 's|@REPORT_BUGS_TO@|$(REPORT_BUGS_TO)|' $^ > $@.new \
>  	&& rm -f $@ && mv $@.new $@ && chmod +x $@
>  
> -$(objpfx)tst-read-chk-cancel: $(shared-thread-library)
> +$(objpfx)tst-chk-cancel: $(shared-thread-library)
> diff --git a/debug/tst-chk-cancel.c b/debug/tst-chk-cancel.c
> new file mode 100644
> index 0000000000..f9ebc4a3f4
> --- /dev/null
> +++ b/debug/tst-chk-cancel.c
> @@ -0,0 +1,269 @@
> +/* Test for required cancellation points in fortified functions (BZ #29274)
> +   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 <array_length.h>
> +#include <errno.h>
> +#include <poll.h>
> +#include <stdbool.h>
> +#include <stdint.h>
> +#include <stdio.h>
> +#include <support/check.h>
> +#include <support/xthread.h>
> +#include <support/xunistd.h>
> +#include <sys/socket.h>
> +
> +/* Cleanup handling test.  */
> +static int cl_called;
> +
> +static void
> +cl (void *arg)
> +{
> +  ++cl_called;
> +}
> +
> +static int fds[2];
> +static pthread_barrier_t barrier;
> +
> +static void *
> +tf_read (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __read_chk because the buffer size
> +     is known, but the read length is non-constant.  */
> +  char c;
> +  if (read (fds[0], &c, (uintptr_t) n) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static void *
> +tf_pread (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __pread_chk because the buffer size
> +     is known, but the read length is non-constant.  */
> +  char c;
> +  if (pread (fds[0], &c, (uintptr_t) n, 0) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static void *
> +tf_pread64 (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __pread64_chk because the buffer size
> +     is known, but the read length is non-constant.  */
> +  char c;
> +  if (pread64 (fds[0], &c, (uintptr_t) n, 0) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static void *
> +tf_poll (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __poll_chk because the pollfd size
> +     is known, but the number of entries is non-constant.  */
> +  struct pollfd pfd = { fds[0], POLLIN, 0 };
> +  if (poll (&pfd, (uintptr_t) n, -1) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static void *
> +tf_ppoll (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __ppoll_chk because the pollfd size
> +     is known, but the number of entries is non-constant.  */
> +  struct pollfd pfd = { fds[0], POLLIN, 0 };
> +  if (ppoll (&pfd, (uintptr_t) n, 0, 0) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static void *
> +tf_recv (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __ppoll_chk because the pollfd size
> +     is known, but the number of entries is non-constant.  */
> +  char c;
> +  if (recv (fds[0], &c, (uintptr_t) n, 0) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static void *
> +tf_recvfrom (void *n)
> +{
> +  pthread_cleanup_push (cl, NULL);
> +
> +  xpthread_barrier_wait (&barrier);
> +
> +  /* This call should be forwarded to __ppoll_chk because the pollfd size
> +     is known, but the number of entries is non-constant.  */
> +  char c;
> +  if (recvfrom (fds[0], &c, (uintptr_t) n, 0, NULL, NULL) != 1)
> +    return (void *) -1L;
> +
> +  pthread_cleanup_pop (0);
> +  return 0;
> +}
> +
> +static struct cancel_tests
> +{
> +  const char *name;
> +  void *(*tf) (void *);
> +  bool only_early;
> +#define ADD_TEST(name, early) { #name, tf_##name, early }
> +} tests[] =
> +{
> +  ADD_TEST (poll,     false),
> +  ADD_TEST (ppoll,    false),
> +  ADD_TEST (pread,    true),
> +  ADD_TEST (pread64,  true),
> +  ADD_TEST (read,     false),
> +  ADD_TEST (recv,     false),
> +  ADD_TEST (recvfrom, false),
> +};
> +
> +/* Set the send buffer of socket S to 1 byte so any send operation
> +   done with WRITE_BUFFER_SIZE bytes will force syscall blocking.  */
> +static void
> +set_socket_buffer (int s)
> +{
> +  int val = 1;
> +  socklen_t len = sizeof (val);
> +
> +  TEST_VERIFY_EXIT (setsockopt (s, SOL_SOCKET, SO_SNDBUF, &val,
> +                    sizeof (val)) == 0);
> +  TEST_VERIFY_EXIT (getsockopt (s, SOL_SOCKET, SO_SNDBUF, &val, &len) == 0);
> +  printf ("%s: got size %d\n", __func__, val);
> +}
> +
> +static int
> +do_test (void)
> +{
> +  xpthread_barrier_init (&barrier, 0, 2);
> +
> +  if (socketpair (AF_UNIX, SOCK_STREAM, 0, fds) != 0)
> +    FAIL_EXIT1 ("socketpair: %m");
> +  set_socket_buffer (fds[1]);
> +
> +  /* This is the !only_early test.  It is a late cancel test that has a sleep
> +     in the main thread in an attempt to allow the child thread to reach and
> +     block on the syscall.  The cancellation should happen with high
> +     probability when the child thread blocked on the syscall, and that is
> +     the intent of the test (syscall cancellation registration complete).  */
> +  for (int i = 0; i < array_length (tests); i++)
> +    {
> +      if (tests[i].only_early)
> +	continue;
> +
> +      xpthread_barrier_init (&barrier, NULL, 2);
> +      /* Reset the counter for the cleanup handler.  */
> +      cl_called = 0;
> +
> +      pthread_t thr = xpthread_create (0, tests[i].tf, (void *) 1L);
> +      /* After this wait the threads cancellation handler is installed.  */
> +      xpthread_barrier_wait (&barrier);
> +
> +      struct timespec ts = { .tv_sec = 0, .tv_nsec = 100000000 };
> +      TEMP_FAILURE_RETRY (clock_nanosleep (CLOCK_REALTIME, 0, &ts, &ts));
> +
> +      xpthread_cancel (thr);
> +
> +      void *status = xpthread_join (thr);
> +      TEST_VERIFY (status == PTHREAD_CANCELED);
> +      TEST_COMPARE (cl_called, 1);
> +
> +      printf ("in-time cancel test of '%s' successful\n", tests[i].name);
> +    }
> +
> +  /* This test is the early cancel version of the first test, and the intent
> +     is to have the cancellation happen at one of two regions:
> +
> +     1. Before the cancellable syscall registers cancellation.
> +     2. After the cancellable syscall registers cancellation.
> +
> +     This test will exercise if syscall cancellation registration is an atomic
> +     operation or not since the transition from the regions is designed to be
> +     atomic.
> +
> +     We can not control when the cancellation happens, but it will happen in
> +     one of the two regions.  The first test (the !only_early version)
> +     attempts to test the second region, while this test attempts to test the
> +     first regiont and the transition with some probability.  */
> +  for (int i = 0; i < array_length (tests); i++)
> +    {
> +      xpthread_barrier_init (&barrier, NULL, 2);
> +      /* Reset the counter for the cleanup handler.  */
> +      cl_called = 0;
> +
> +      /* After this wait the cancellation handler is in place.  */
> +      pthread_t thr = xpthread_create (0, tests[i].tf, NULL);
> +
> +      xpthread_cancel (thr);
> +      xpthread_barrier_wait (&barrier);

Shouldn't this be:

xpthread_barrier_wait (&barrier);
xpthread_cancel (thr);

You want to:

(a) Make sure a cancellation handler is registered.
(b) Deliver the signal *before* you reach the syscall __pthread_enable_asyncancel.
(c) Observe the cancelled bit early and act upon it.

The test is effectively very similar to the first test but with no wait to allow
the thread to get to and block on the syscall.

> +
> +      void *status = xpthread_join (thr);
> +      TEST_VERIFY (status == PTHREAD_CANCELED);
> +      TEST_COMPARE (cl_called, 1);
> +
> +      printf ("early cancel test of '%s' successful\n", tests[i].name);
> +    }
> +
> +  xpthread_barrier_destroy (&barrier);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/debug/tst-read-chk-cancel.c b/debug/tst-read-chk-cancel.c
> deleted file mode 100644
> index 7e06afb596..0000000000
> --- a/debug/tst-read-chk-cancel.c
> +++ /dev/null
> @@ -1,50 +0,0 @@
> -/* Test that __read_chk is a cancellation point (BZ #29274)
> -   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 <stdint.h>
> -#include <support/xunistd.h>
> -#include <support/xthread.h>
> -
> -static int pipe_fds[2];
> -static pthread_barrier_t barrier;
> -
> -static void *
> -read_thread (void *n)
> -{
> -  xpthread_barrier_wait (&barrier);
> -  char c;
> -  /* This call should be forwarded to __read_chk because the buffer size
> -     is known, but the read length is non-constant.  */
> -  if (read (pipe_fds[0], &c, (uintptr_t) n) != 1)
> -    return (void *) -1L;
> -  return 0;
> -}
> -
> -static int
> -do_test (void)
> -{
> -  xpthread_barrier_init (&barrier, 0, 2);
> -  xpipe (pipe_fds);
> -  pthread_t thr = xpthread_create (0, read_thread, (void *) 1L);
> -  xpthread_barrier_wait (&barrier);
> -  xpthread_cancel (thr);
> -  xpthread_join (thr);
> -  return 0;
> -}
> -
> -#include <support/test-driver.c>


-- 
Cheers,
Carlos.