[v2,2/2] Block all signals on timer_create thread (BZ#10815)
diff mbox series

Message ID 20191231193129.2590-2-adhemerval.zanella@linaro.org
State New
Headers show
Series
  • [1/2] linux: Reserve a new signal for SIGTIMER
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Commit Message

Adhemerval Zanella Dec. 31, 2019, 7:31 p.m. UTC
Changes from previous version:

  - Use xpthread on tst-timer-sigmask.
  - It does not block SIGCANCEL and it adds tst-cancel28.c to check
    if the created thread is cancellable.

--

The behavior of the signal mask on threads created by timer_create
for SIGEV_THREAD timers are implementation-defined and glibc explicit
unblocks all signals before calling the user-defined function.

This behavior, although not incorrect standard-wise, opens a race if a
program using a blocked rt-signal plus sigwaitinfo (and without an
installed signal handler for the rt-signal) receives a signal while
executing the used-defined function for SIGEV_THREAD.

A better alternative discussed in bug report is to rather block all
signals (besides the internal ones not available to application
usage).

This patch fixes this issue by only unblocking SIGSETXID (used on
set*uid function) and SIGCANCEL (used for thread cancellation).

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 nptl/Makefile                              |  5 +-
 nptl/tst-cancel28.c                        | 80 ++++++++++++++++++
 rt/Makefile                                |  7 +-
 rt/tst-timer-sigmask.c                     | 85 +++++++++++++++++++
 sysdeps/unix/sysv/linux/internal-signals.h | 20 +++++
 sysdeps/unix/sysv/linux/timer_routines.c   | 96 ++++++++--------------
 6 files changed, 227 insertions(+), 66 deletions(-)
 create mode 100644 nptl/tst-cancel28.c
 create mode 100644 rt/tst-timer-sigmask.c

Patch
diff mbox series

diff --git a/nptl/Makefile b/nptl/Makefile
index 4a57213ddb..ca4d14d541 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -286,7 +286,7 @@  tests = tst-attr1 tst-attr2 tst-attr3 tst-default-attr \
 	tst-cancel11 tst-cancel12 tst-cancel13 tst-cancel14 tst-cancel15 \
 	tst-cancel16 tst-cancel17 tst-cancel18 tst-cancel19 tst-cancel20 \
 	tst-cancel21 tst-cancel22 tst-cancel23 tst-cancel24 \
-	tst-cancel26 tst-cancel27 \
+	tst-cancel26 tst-cancel27 tst-cancel28 \
 	tst-cancel-self tst-cancel-self-cancelstate \
 	tst-cancel-self-canceltype tst-cancel-self-testcancel \
 	tst-cleanup0 tst-cleanup1 tst-cleanup2 tst-cleanup3 tst-cleanup4 \
@@ -600,6 +600,9 @@  $(objpfx)tst-tls6.out: tst-tls6.sh $(objpfx)tst-tls5 \
 	$(BASH) $< $(common-objpfx) '$(test-via-rtld-prefix)' \
 	  '$(test-wrapper-env)' '$(run-program-env)' > $@; \
 	$(evaluate-test)
+$(objpfx)tst-cancel28: $(common-objpfx)rt/librt.so
+else
+$(objpfx)tst-cancel28: $(common-objpfx)rt/librt.a
 endif
 
 $(objpfx)tst-join7: $(libdl) $(shared-thread-library)
diff --git a/nptl/tst-cancel28.c b/nptl/tst-cancel28.c
new file mode 100644
index 0000000000..ad70aeb548
--- /dev/null
+++ b/nptl/tst-cancel28.c
@@ -0,0 +1,80 @@ 
+/* Check if the thread created by POSIX timer using SIGEV_THREAD is
+   cancellable.
+   Copyright (C) 2019 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 <stdio.h>
+#include <time.h>
+#include <signal.h>
+#include <unistd.h>
+#include <stdbool.h>
+
+#include <support/check.h>
+#include <support/test-driver.h>
+#include <support/xthread.h>
+
+static pthread_barrier_t barrier;
+static pthread_t timer_thread;
+
+static void
+cl (void *arg)
+{
+  xpthread_barrier_wait (&barrier);
+}
+
+static void
+thread_handler (union sigval sv)
+{
+  timer_thread = pthread_self ();
+
+  xpthread_barrier_wait (&barrier);
+
+  pthread_cleanup_push (cl, NULL);
+  while (1)
+    clock_nanosleep (CLOCK_REALTIME, 0, &(struct timespec) { 1, 0 }, NULL);
+  pthread_cleanup_pop (0);
+}
+
+static int
+do_test (void)
+{
+  struct sigevent sev = { 0 };
+  sev.sigev_notify = SIGEV_THREAD;
+  sev.sigev_notify_function = &thread_handler;
+
+  timer_t timerid;
+  TEST_COMPARE (timer_create (CLOCK_REALTIME, &sev, &timerid), 0);
+
+  xpthread_barrier_init (&barrier, NULL, 2);
+
+  struct itimerspec trigger = { 0 };
+  trigger.it_value.tv_nsec = 1000000;
+  TEST_COMPARE (timer_settime (timerid, 0, &trigger, NULL), 0);
+
+  xpthread_barrier_wait (&barrier);
+
+  xpthread_cancel (timer_thread);
+
+  xpthread_barrier_init (&barrier, NULL, 2);
+  xpthread_barrier_wait (&barrier);
+
+  return 0;
+}
+
+/* A stall in cancellation is a regression.  */
+#define TIMEOUT 5
+#include <support/test-driver.c>
diff --git a/rt/Makefile b/rt/Makefile
index 6c8365e0c0..a7a82879c7 100644
--- a/rt/Makefile
+++ b/rt/Makefile
@@ -47,6 +47,7 @@  tests := tst-shm tst-timer tst-timer2 \
 	 tst-timer3 tst-timer4 tst-timer5 \
 	 tst-cpuclock2 tst-cputimer1 tst-cputimer2 tst-cputimer3 \
 	 tst-shm-cancel
+tests-internal := tst-timer-sigmask
 
 extra-libs := librt
 extra-libs-others := $(extra-libs)
@@ -63,9 +64,11 @@  LDFLAGS-rt.so = -Wl,--enable-new-dtags,-z,nodelete
 $(objpfx)librt.so: $(shared-thread-library)
 
 ifeq (yes,$(build-shared))
-$(addprefix $(objpfx),$(tests)): $(objpfx)librt.so $(shared-thread-library)
+$(addprefix $(objpfx),$(tests) $(tests-internal)): \
+	$(objpfx)librt.so $(shared-thread-library)
 else
-$(addprefix $(objpfx),$(tests)): $(objpfx)librt.a $(static-thread-library)
+$(addprefix $(objpfx),$(tests)) $(tests-internal): \
+	$(objpfx)librt.a $(static-thread-library)
 endif
 
 tst-mqueue7-ARGS = -- $(host-test-program-cmd)
diff --git a/rt/tst-timer-sigmask.c b/rt/tst-timer-sigmask.c
new file mode 100644
index 0000000000..063004120a
--- /dev/null
+++ b/rt/tst-timer-sigmask.c
@@ -0,0 +1,85 @@ 
+/* Check resulting signal mask from POSIX timer using SIGEV_THREAD.
+   Copyright (C) 2019 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 <stdio.h>
+#include <time.h>
+#include <signal.h>
+#include <stdbool.h>
+
+#include <support/check.h>
+#include <support/test-driver.h>
+#include <support/xthread.h>
+
+#include <internal-signals.h>
+
+static pthread_barrier_t barrier;
+static bool thread_handler_failure = false;
+
+static void
+thread_handler (union sigval sv)
+{
+  sigset_t ss;
+  sigprocmask (SIG_BLOCK, NULL, &ss);
+  if (test_verbose > 0)
+    printf ("%s: blocked signal mask = { ", __func__);
+  for (int sig = 1; sig < NSIG; sig++)
+    {
+#ifdef __linux__
+      /* POSIX timers threads created to handle SIGEV_THREAD block all
+	 signals except SIGKILL, SIGSTOP and glibc internals one except
+	 SIGTIMER.  */
+      if (!sigismember (&ss, sig)
+	  && (sig != SIGSETXID && sig != SIGCANCEL
+	      && sig != SIGKILL && sig != SIGSTOP))
+	{
+	  thread_handler_failure = true;
+	}
+#endif
+      if (test_verbose && sigismember (&ss, sig))
+	printf ("%d, ", sig);
+    }
+  if (test_verbose > 0)
+    printf ("}\n");
+
+  xpthread_barrier_wait (&barrier);
+}
+
+static int
+do_test (void)
+{
+  struct sigevent sev = { 0 };
+  sev.sigev_notify = SIGEV_THREAD;
+  sev.sigev_notify_function = &thread_handler;
+
+  timer_t timerid;
+  TEST_COMPARE (timer_create (CLOCK_REALTIME, &sev, &timerid), 0);
+
+  xpthread_barrier_init (&barrier, NULL, 2);
+
+  struct itimerspec trigger = { 0 };
+  trigger.it_value.tv_nsec = 1000000;
+  TEST_COMPARE (timer_settime (timerid, 0, &trigger, NULL), 0);
+
+  xpthread_barrier_wait (&barrier);
+
+  TEST_COMPARE (thread_handler_failure, false);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/internal-signals.h b/sysdeps/unix/sysv/linux/internal-signals.h
index 06d1d38b7f..df406ea522 100644
--- a/sysdeps/unix/sysv/linux/internal-signals.h
+++ b/sysdeps/unix/sysv/linux/internal-signals.h
@@ -65,6 +65,17 @@  static const sigset_t sigall_set = {
    .__val = {[0 ...  _SIGSET_NWORDS-1 ] =  -1 }
 };
 
+static const sigset_t sigtimer_set = {
+#if ULONG_MAX == 0xffffffff
+  .__val = { [0]                      = 0,
+             [1]                      = __sigmask (SIGTIMER),
+             [2 ... _SIGSET_NWORDS-1] = 0 }
+#else
+  .__val = { [0]                      = __sigmask (SIGTIMER),
+	     [1 ... _SIGSET_NWORDS-1] = 0 }
+#endif
+};
+
 /* Block all signals, including internal glibc ones.  */
 static inline void
 __libc_signal_block_all (sigset_t *set)
@@ -85,6 +96,15 @@  __libc_signal_block_app (sigset_t *set)
 			 _NSIG / 8);
 }
 
+/* Block only the SIGTIMER set.  */
+static inline void
+__libc_signal_block_sigtimer (sigset_t *set)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  INTERNAL_SYSCALL_CALL (rt_sigprocmask, err, SIG_BLOCK, &sigtimer_set, set,
+			 _NSIG / 8);
+}
+
 /* Restore current process signal mask.  */
 static inline void
 __libc_signal_restore_set (const sigset_t *set)
diff --git a/sysdeps/unix/sysv/linux/timer_routines.c b/sysdeps/unix/sysv/linux/timer_routines.c
index 84213dd4f7..832cc9190a 100644
--- a/sysdeps/unix/sysv/linux/timer_routines.c
+++ b/sysdeps/unix/sysv/linux/timer_routines.c
@@ -42,14 +42,6 @@  struct thread_start_data
 static void *
 timer_sigev_thread (void *arg)
 {
-  /* The parent thread has all signals blocked.  This is a bit
-     surprising for user code, although valid.  We unblock all
-     signals.  */
-  sigset_t ss;
-  sigemptyset (&ss);
-  INTERNAL_SYSCALL_DECL (err);
-  INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, &ss, NULL, _NSIG / 8);
-
   struct thread_start_data *td = (struct thread_start_data *) arg;
 
   void (*thrfunc) (sigval_t) = td->thrfunc;
@@ -69,65 +61,49 @@  timer_sigev_thread (void *arg)
 static void *
 timer_helper_thread (void *arg)
 {
-  /* Wait for the SIGTIMER signal, allowing the setXid signal, and
-     none else.  */
-  sigset_t ss;
-  sigemptyset (&ss);
-  __sigaddset (&ss, SIGTIMER);
-
   /* Endless loop of waiting for signals.  The loop is only ended when
      the thread is canceled.  */
   while (1)
     {
       siginfo_t si;
 
-      /* sigwaitinfo cannot be used here, since it deletes
-	 SIGCANCEL == SIGTIMER from the set.  */
-
-      /* XXX The size argument hopefully will have to be changed to the
-	 real size of the user-level sigset_t.  */
-      int result = SYSCALL_CANCEL (rt_sigtimedwait, &ss, &si, NULL, _NSIG / 8);
-
-      if (result > 0)
+      while (sigwaitinfo (&sigtimer_set, &si) < 0);
+      if (si.si_code == SI_TIMER)
 	{
-	  if (si.si_code == SI_TIMER)
-	    {
-	      struct timer *tk = (struct timer *) si.si_ptr;
+	  struct timer *tk = (struct timer *) si.si_ptr;
+
+	  /* Check the timer is still used and will not go away
+	     while we are reading the values here.  */
+	  pthread_mutex_lock (&__active_timer_sigev_thread_lock);
 
-	      /* Check the timer is still used and will not go away
-		 while we are reading the values here.  */
-	      pthread_mutex_lock (&__active_timer_sigev_thread_lock);
+	  struct timer *runp = __active_timer_sigev_thread;
+	  while (runp != NULL)
+	    if (runp == tk)
+	      break;
+	  else
+	    runp = runp->next;
 
-	      struct timer *runp = __active_timer_sigev_thread;
-	      while (runp != NULL)
-		if (runp == tk)
-		  break;
-		else
-		  runp = runp->next;
+	  if (runp != NULL)
+	    {
+	      struct thread_start_data *td = malloc (sizeof (*td));
 
-	      if (runp != NULL)
+	      /* There is not much we can do if the allocation fails.  */
+	      if (td != NULL)
 		{
-		  struct thread_start_data *td = malloc (sizeof (*td));
-
-		  /* There is not much we can do if the allocation fails.  */
-		  if (td != NULL)
-		    {
-		      /* This is the signal we are waiting for.  */
-		      td->thrfunc = tk->thrfunc;
-		      td->sival = tk->sival;
-
-		      pthread_t th;
-		      (void) pthread_create (&th, &tk->attr,
-					     timer_sigev_thread, td);
-		    }
-		}
+		  /* This is the signal we are waiting for.  */
+		  td->thrfunc = tk->thrfunc;
+		  td->sival = tk->sival;
 
-	      pthread_mutex_unlock (&__active_timer_sigev_thread_lock);
+		  pthread_t th;
+		  pthread_create (&th, &tk->attr, timer_sigev_thread, td);
+		}
 	    }
-	  else if (si.si_code == SI_TKILL)
-	    /* The thread is canceled.  */
-	    pthread_exit (NULL);
+
+	  pthread_mutex_unlock (&__active_timer_sigev_thread_lock);
 	}
+      else if (si.si_code == SI_TKILL)
+	/* The thread is canceled.  */
+	pthread_exit (NULL);
     }
 }
 
@@ -161,15 +137,10 @@  __start_helper_thread (void)
 
   /* Block all signals in the helper thread but SIGSETXID.  To do this
      thoroughly we temporarily have to block all signals here.  The
-     helper can lose wakeups if SIGCANCEL is not blocked throughout,
-     but sigfillset omits it SIGSETXID.  So, we add SIGCANCEL back
-     explicitly here.  */
+     helper can lose wakeups if SIGTIMER is not blocked throughout.  */
   sigset_t ss;
-  sigset_t oss;
-  sigfillset (&ss);
-  __sigaddset (&ss, SIGTIMER);
-  INTERNAL_SYSCALL_DECL (err);
-  INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, &ss, &oss, _NSIG / 8);
+  __libc_signal_block_app (&ss);
+  __libc_signal_block_sigtimer (NULL);
 
   /* Create the helper thread for this timer.  */
   pthread_t th;
@@ -179,8 +150,7 @@  __start_helper_thread (void)
     __helper_tid = ((struct pthread *) th)->tid;
 
   /* Restore the signal mask.  */
-  INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, &oss, NULL,
-		    _NSIG / 8);
+  __libc_signal_restore_set (&ss);
 
   /* No need for the attribute anymore.  */
   (void) pthread_attr_destroy (&attr);