Re: [PATCH v4] debug: test for more required cacellation points (BZ# 29274)

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

On 8/30/22 09:53, 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 x86_64-linux-gnu and aarch64-linux-gnu.
> 
> Co-authored-by: Andreas Schwab <schwab@suse.de>

Thanks for working through the details of what you were trying to test
with these patches. This version looks good to me.

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

> ---
>  debug/Makefile              |   6 +-
>  debug/tst-chk-cancel.c      | 263 ++++++++++++++++++++++++++++++++++++
>  debug/tst-read-chk-cancel.c |  50 -------
>  3 files changed, 266 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..5c6e22697f
> --- /dev/null
> +++ b/debug/tst-chk-cancel.c
> @@ -0,0 +1,263 @@
> +/* 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 is a early cancel test that happens before the syscall is issued.
> +     In this case there is no signal involved, pthread_cancel will just mark
> +     the target thread canceled, since asynchronous mode is not set, and the
> +     cancellable entrypoint will check if the thread is set as cancelled and
> +     exit early.

OK. Agreed.

> +
> +     Keep in mind that neither pthread_barrier_wait nor pthread_cleanup_push
> +     act as cancellation entrypoints.  */

OK. Correct! Great comment.

> +  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);
> +
> +      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.