Re: [PATCH v4 2/4] Filter out NPTL internal signals (BZ #22391)

[Zack Weinberg <zackw@panix.com>]

LGTM except I think sysdeps/generic/internal-signals.h should define
all of the functions that sysdeps/u/s/l/internal-signals.h does.

On Tue, Apr 3, 2018 at 10:24 AM, Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
> If no one opposes, I will commit this shortly.
>
> On 19/02/2018 14:50, Adhemerval Zanella wrote:
>> Ping.
>>
>> On 12/02/2018 10:42, Adhemerval Zanella wrote:
>>> This patch filters out the internal NPTL signals (SIGCANCEL/SIGTIMER and
>>> SIGSETXID) from signal functions.  GLIBC on Linux requires both signals to
>>> proper implement pthread cancellation, posix timers, and set*id posix
>>> thread synchronization.
>>>
>>> And not filtering out the internal signal is troublesome:
>>>
>>>   - A conformant program on a architecture that does not filter out the
>>>     signals might inadvertently disable pthread asynchronous cancellation,
>>>     set*id synchronization or posix timers.
>>>
>>>   - It might also to security issues if SIGSETXID is masked and set*id
>>>     functions are called (some threads might have effective user or group
>>>     id different from the rest).
>>>
>>> The changes are basically:
>>>
>>>   - Change __is_internal_signal to bool and used on all signal function
>>>     that has a signal number as input.  Also for signal function which accepts
>>>     signals sets (sigset_t) it assumes that canonical function were used to
>>>     add/remove signals which lead to some input simplification.
>>>
>>>   - Fix tst-sigset.c to avoid check for SIGCANCEL/SIGTIMER and SIGSETXID.
>>>     It is rewritten to check each signal indidually and to check realtime
>>>     signals using canonical macros.
>>>
>>>   - Add generic __clear_internal_signals and __is_internal_signal
>>>     version since both symbols are used on generic implementations.
>>>
>>>   - Remove superflous sysdeps/nptl/sigfillset.c.
>>>
>>>   - Remove superflous SIGTIMER handling on Linux __is_internal_signal
>>>     since it is the same of SIGCANCEL.
>>>
>>>   - Remove dangling define and obvious comment on nptl/sigaction.c.
>>>
>>> Checked on x86_64-linux-gnu.
>>>
>>>      [BZ #22391]
>>>      * nptl/sigaction.c (__sigaction): Use __is_internal_signal to
>>>      check for internal nptl signals.
>>>      * signal/sigaddset.c (sigaddset): Likewise.
>>>      * signal/sigdelset.c (sigdelset): Likewise.
>>>      * sysdeps/posix/signal.c (__bsd_signal): Likewise.
>>>      * sysdeps/posix/sigset.c (sigset): Call and check sigaddset return
>>>      value.
>>>      * signal/sigfillset.c (sigfillset): User __clear_internal_signals
>>>      to filter out internal nptl signals.
>>>      * signal/tst-sigset.c (do_test): Check ech signal indidually and
>>>      also check realtime signals using standard macros.
>>>      * sysdeps/nptl/nptl-signals.h (__clear_internal_signals,
>>>      __is_internal_signal): New functions.
>>>      * sysdeps/nptl/sigfillset.c: Remove file.
>>>      * sysdeps/unix/sysv/linux/nptl-signals.h (__is_internal_signal):
>>>      Change return to bool.
>>>      (__clear_internal_signals): Remove SIGTIMER clean since it is
>>>      equal to SIGCANEL on Linux.
>>>      * sysdeps/unix/sysv/linux/sigtimedwait.c (__sigtimedwait): Assume
>>>      signal set was constructed using standard functions.
>>>      * sysdeps/unix/sysv/linux/sigwait.c (do_sigtwait): Likewise.
>>>
>>> Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>>> Reported-by: Yury Norov <ynorov@caviumnetworks.com>
>>> ---
>>>  ChangeLog                                  | 23 ++++++++
>>>  nptl/sigaction.c                           | 14 +----
>>>  signal/sigaction.c                         |  2 +-
>>>  signal/sigaddset.c                         |  5 +-
>>>  signal/sigdelset.c                         |  5 +-
>>>  signal/sigfillset.c                        | 10 +---
>>>  signal/tst-sigset.c                        | 92 ++++++++++++++++++++++--------
>>>  sysdeps/generic/internal-signals.h         | 11 ++++
>>>  sysdeps/nptl/sigfillset.c                  | 20 -------
>>>  sysdeps/posix/signal.c                     |  5 +-
>>>  sysdeps/posix/sigset.c                     | 10 +---
>>>  sysdeps/unix/sysv/linux/internal-signals.h |  4 +-
>>>  sysdeps/unix/sysv/linux/sigtimedwait.c     | 17 +-----
>>>  13 files changed, 122 insertions(+), 96 deletions(-)
>>>  delete mode 100644 sysdeps/nptl/sigfillset.c
>>>
>>> diff --git a/nptl/sigaction.c b/nptl/sigaction.c
>>> index ddf6f5e..79b6fdc 100644
>>> --- a/nptl/sigaction.c
>>> +++ b/nptl/sigaction.c
>>> @@ -16,22 +16,12 @@
>>>     License along with the GNU C Library; if not, see
>>>     <http://www.gnu.org/licenses/>.  */
>>>
>>> -
>>> -/* This is no complete implementation.  The file is meant to be
>>> -   included in the real implementation to provide the wrapper around
>>> -   __libc_sigaction.  */
>>> -
>>> -#include <nptl/pthreadP.h>
>>> -
>>> -/* We use the libc implementation but we tell it to not allow
>>> -   SIGCANCEL or SIGTIMER to be handled.  */
>>> -#define LIBC_SIGACTION      1
>>> -
>>> +#include <internal-signals.h>
>>>
>>>  int
>>>  __sigaction (int sig, const struct sigaction *act, struct sigaction *oact)
>>>  {
>>> -  if (__glibc_unlikely (sig == SIGCANCEL || sig == SIGSETXID))
>>> +  if (sig <= 0 || sig >= NSIG || __is_internal_signal (sig))
>>>      {
>>>        __set_errno (EINVAL);
>>>        return -1;
>>> diff --git a/signal/sigaction.c b/signal/sigaction.c
>>> index f761ca2..c99001a 100644
>>> --- a/signal/sigaction.c
>>> +++ b/signal/sigaction.c
>>> @@ -24,7 +24,7 @@
>>>  int
>>>  __sigaction (int sig, const struct sigaction *act, struct sigaction *oact)
>>>  {
>>> -  if (sig <= 0 || sig >= NSIG)
>>> +  if (sig <= 0 || sig >= NSIG || __is_internal_signal (sig))
>>>      {
>>>        __set_errno (EINVAL);
>>>        return -1;
>>> diff --git a/signal/sigaddset.c b/signal/sigaddset.c
>>> index d310890..7238df4 100644
>>> --- a/signal/sigaddset.c
>>> +++ b/signal/sigaddset.c
>>> @@ -17,13 +17,14 @@
>>>
>>>  #include <errno.h>
>>>  #include <signal.h>
>>> -#include <sigsetops.h>
>>> +#include <internal-signals.h>
>>>
>>>  /* Add SIGNO to SET.  */
>>>  int
>>>  sigaddset (sigset_t *set, int signo)
>>>  {
>>> -  if (set == NULL || signo <= 0 || signo >= NSIG)
>>> +  if (set == NULL || signo <= 0 || signo >= NSIG
>>> +      || __is_internal_signal (signo))
>>>      {
>>>        __set_errno (EINVAL);
>>>        return -1;
>>> diff --git a/signal/sigdelset.c b/signal/sigdelset.c
>>> index cd83dda..011978c 100644
>>> --- a/signal/sigdelset.c
>>> +++ b/signal/sigdelset.c
>>> @@ -17,13 +17,14 @@
>>>
>>>  #include <errno.h>
>>>  #include <signal.h>
>>> -#include <sigsetops.h>
>>> +#include <internal-signals.h>
>>>
>>>  /* Add SIGNO to SET.  */
>>>  int
>>>  sigdelset (sigset_t *set, int signo)
>>>  {
>>> -  if (set == NULL || signo <= 0 || signo >= NSIG)
>>> +  if (set == NULL || signo <= 0 || signo >= NSIG
>>> +      || __is_internal_signal (signo))
>>>      {
>>>        __set_errno (EINVAL);
>>>        return -1;
>>> diff --git a/signal/sigfillset.c b/signal/sigfillset.c
>>> index e586fd9..83dd583 100644
>>> --- a/signal/sigfillset.c
>>> +++ b/signal/sigfillset.c
>>> @@ -18,6 +18,7 @@
>>>  #include <errno.h>
>>>  #include <signal.h>
>>>  #include <string.h>
>>> +#include <internal-signals.h>
>>>
>>>  /* Set all signals in SET.  */
>>>  int
>>> @@ -31,14 +32,7 @@ sigfillset (sigset_t *set)
>>>
>>>    memset (set, 0xff, sizeof (sigset_t));
>>>
>>> -  /* If the implementation uses a cancellation signal don't set the bit.  */
>>> -#ifdef SIGCANCEL
>>> -  __sigdelset (set, SIGCANCEL);
>>> -#endif
>>> -  /* Likewise for the signal to implement setxid.  */
>>> -#ifdef SIGSETXID
>>> -  __sigdelset (set, SIGSETXID);
>>> -#endif
>>> +  __clear_internal_signals (set);
>>>
>>>    return 0;
>>>  }
>>> diff --git a/signal/tst-sigset.c b/signal/tst-sigset.c
>>> index d47adcc..a2b764d 100644
>>> --- a/signal/tst-sigset.c
>>> +++ b/signal/tst-sigset.c
>>> @@ -1,43 +1,85 @@
>>>  /* Test sig*set functions.  */
>>>
>>>  #include <signal.h>
>>> -#include <stdio.h>
>>>
>>> -#define TEST_FUNCTION do_test ()
>>> +#include <support/check.h>
>>> +
>>>  static int
>>>  do_test (void)
>>>  {
>>> -  int result = 0;
>>> -  int sig = -1;
>>> +  sigset_t set;
>>> +  TEST_VERIFY (sigemptyset (&set) == 0);
>>>
>>> -#define TRY(call)                                                         \
>>> -  if (call)                                                               \
>>> -    {                                                                             \
>>> -      printf ("%s (sig = %d): %m\n", #call, sig);                         \
>>> -      result = 1;                                                         \
>>> -    }                                                                             \
>>> -  else
>>> +#define VERIFY(set, sig)                    \
>>> +  TEST_VERIFY (sigismember (&set, sig) == 0);       \
>>> +  TEST_VERIFY (sigaddset (&set, sig) == 0); \
>>> +  TEST_VERIFY (sigismember (&set, sig) != 0);       \
>>> +  TEST_VERIFY (sigdelset (&set, sig) == 0); \
>>> +  TEST_VERIFY (sigismember (&set, sig) == 0)
>>>
>>> +  /* ISO C99 signals.  */
>>> +  VERIFY (set, SIGINT);
>>> +  VERIFY (set, SIGILL);
>>> +  VERIFY (set, SIGABRT);
>>> +  VERIFY (set, SIGFPE);
>>> +  VERIFY (set, SIGSEGV);
>>> +  VERIFY (set, SIGTERM);
>>>
>>> -  sigset_t set;
>>> -  TRY (sigemptyset (&set) != 0);
>>> +  /* Historical signals specified by POSIX. */
>>> +  VERIFY (set, SIGHUP);
>>> +  VERIFY (set, SIGQUIT);
>>> +  VERIFY (set, SIGTRAP);
>>> +  VERIFY (set, SIGKILL);
>>> +  VERIFY (set, SIGBUS);
>>> +  VERIFY (set, SIGSYS);
>>> +  VERIFY (set, SIGPIPE);
>>> +  VERIFY (set, SIGALRM);
>>> +
>>> +  /* New(er) POSIX signals (1003.1-2008, 1003.1-2013).  */
>>> +  VERIFY (set, SIGURG);
>>> +  VERIFY (set, SIGSTOP);
>>> +  VERIFY (set, SIGTSTP);
>>> +  VERIFY (set, SIGCONT);
>>> +  VERIFY (set, SIGCHLD);
>>> +  VERIFY (set, SIGTTIN);
>>> +  VERIFY (set, SIGTTOU);
>>> +  VERIFY (set, SIGPOLL);
>>> +  VERIFY (set, SIGXCPU);
>>> +  VERIFY (set, SIGXFSZ);
>>> +  VERIFY (set, SIGVTALRM);
>>> +  VERIFY (set, SIGPROF);
>>> +  VERIFY (set, SIGUSR1);
>>> +  VERIFY (set, SIGUSR2);
>>> +
>>> +  /* Nonstandard signals found in all modern POSIX systems
>>> +     (including both BSD and Linux).  */
>>> +  VERIFY (set, SIGWINCH);
>>>
>>> -#ifdef SIGRTMAX
>>> -  int max_sig = SIGRTMAX;
>>> -#else
>>> -  int max_sig = NSIG - 1;
>>> +  /* Arch-specific signals.  */
>>> +#ifdef SIGEMT
>>> +  VERIFY (set, SIGEMT);
>>> +#endif
>>> +#ifdef SIGLOST
>>> +  VERIFY (set, SIGLOST);
>>> +#endif
>>> +#ifdef SIGINFO
>>> +  VERIFY (set, SIGINFO);
>>> +#endif
>>> +#ifdef SIGSTKFLT
>>> +  VERIFY (set, SIGSTKFLT);
>>> +#endif
>>> +#ifdef SIGPWR
>>> +  VERIFY (set, SIGPWR);
>>>  #endif
>>>
>>> -  for (sig = 1; sig <= max_sig; ++sig)
>>> +  /* Read-time signals (POSIX.1b real-time extensions).  If they are
>>> +     supported SIGRTMAX value is greater than SIGRTMIN.  */
>>> +  for (int rtsig = SIGRTMIN; rtsig <= SIGRTMAX; rtsig++)
>>>      {
>>> -      TRY (sigismember (&set, sig) != 0);
>>> -      TRY (sigaddset (&set, sig) != 0);
>>> -      TRY (sigismember (&set, sig) == 0);
>>> -      TRY (sigdelset (&set, sig) != 0);
>>> -      TRY (sigismember (&set, sig) != 0);
>>> +      VERIFY (set, rtsig);
>>>      }
>>>
>>> -  return result;
>>> +  return 0;
>>>  }
>>>
>>> -#include "../test-skeleton.c"
>>> +#include <support/test-driver.c>
>>> diff --git a/sysdeps/generic/internal-signals.h b/sysdeps/generic/internal-signals.h
>>> index 01e5b75..ab0b22e 100644
>>> --- a/sysdeps/generic/internal-signals.h
>>> +++ b/sysdeps/generic/internal-signals.h
>>> @@ -15,3 +15,14 @@
>>>     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/>.  */
>>> +
>>> +static inline void
>>> +__clear_internal_signals (sigset_t *set)
>>> +{
>>> +}
>>> +
>>> +static inline bool
>>> +__is_internal_signal (int sig)
>>> +{
>>> +  return false;
>>> +}
>>> diff --git a/sysdeps/nptl/sigfillset.c b/sysdeps/nptl/sigfillset.c
>>> deleted file mode 100644
>>> index 94a7680..0000000
>>> --- a/sysdeps/nptl/sigfillset.c
>>> +++ /dev/null
>>> @@ -1,20 +0,0 @@
>>> -/* Copyright (C) 2003-2018 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 <nptl/pthreadP.h>
>>> -
>>> -#include <signal/sigfillset.c>
>>> diff --git a/sysdeps/posix/signal.c b/sysdeps/posix/signal.c
>>> index a4a0875..8a135c7 100644
>>> --- a/sysdeps/posix/signal.c
>>> +++ b/sysdeps/posix/signal.c
>>> @@ -18,8 +18,8 @@
>>>
>>>  #include <errno.h>
>>>  #include <signal.h>
>>> -#include <string.h> /* For the real memset prototype.  */
>>>  #include <sigsetops.h>
>>> +#include <internal-signals.h>
>>>
>>>  sigset_t _sigintr attribute_hidden;         /* Set by siginterrupt.  */
>>>
>>> @@ -31,7 +31,8 @@ __bsd_signal (int sig, __sighandler_t handler)
>>>    struct sigaction act, oact;
>>>
>>>    /* Check signal extents to protect __sigismember.  */
>>> -  if (handler == SIG_ERR || sig < 1 || sig >= NSIG)
>>> +  if (handler == SIG_ERR || sig < 1 || sig >= NSIG
>>> +      || __is_internal_signal (sig))
>>>      {
>>>        __set_errno (EINVAL);
>>>        return SIG_ERR;
>>> diff --git a/sysdeps/posix/sigset.c b/sysdeps/posix/sigset.c
>>> index b62aa3c..6ab4a48 100644
>>> --- a/sysdeps/posix/sigset.c
>>> +++ b/sysdeps/posix/sigset.c
>>> @@ -31,15 +31,9 @@ sigset (int sig, __sighandler_t disp)
>>>    sigset_t set;
>>>    sigset_t oset;
>>>
>>> -  /* Check signal extents to protect __sigismember.  */
>>> -  if (disp == SIG_ERR || sig < 1 || sig >= NSIG)
>>> -    {
>>> -      __set_errno (EINVAL);
>>> -      return SIG_ERR;
>>> -    }
>>> -
>>>    __sigemptyset (&set);
>>> -  __sigaddset (&set, sig);
>>> +  if (sigaddset (&set, sig) < 0)
>>> +    return SIG_ERR;
>>>
>>>    if (disp == SIG_HOLD)
>>>      {
>>> diff --git a/sysdeps/unix/sysv/linux/internal-signals.h b/sysdeps/unix/sysv/linux/internal-signals.h
>>> index e007372..5ff4cf8 100644
>>> --- a/sysdeps/unix/sysv/linux/internal-signals.h
>>> +++ b/sysdeps/unix/sysv/linux/internal-signals.h
>>> @@ -21,6 +21,8 @@
>>>
>>>  #include <signal.h>
>>>  #include <sigsetops.h>
>>> +#include <stdbool.h>
>>> +#include <sysdep.h>
>>>
>>>  /* The signal used for asynchronous cancelation.  */
>>>  #define SIGCANCEL       __SIGRTMIN
>>> @@ -37,7 +39,7 @@
>>>
>>>
>>>  /* Return is sig is used internally.  */
>>> -static inline int
>>> +static inline bool
>>>  __is_internal_signal (int sig)
>>>  {
>>>    return (sig == SIGCANCEL) || (sig == SIGSETXID);
>>> diff --git a/sysdeps/unix/sysv/linux/sigtimedwait.c b/sysdeps/unix/sysv/linux/sigtimedwait.c
>>> index 051a285..b4de885 100644
>>> --- a/sysdeps/unix/sysv/linux/sigtimedwait.c
>>> +++ b/sysdeps/unix/sysv/linux/sigtimedwait.c
>>> @@ -24,21 +24,8 @@ int
>>>  __sigtimedwait (const sigset_t *set, siginfo_t *info,
>>>              const struct timespec *timeout)
>>>  {
>>> -  sigset_t tmpset;
>>> -  if (set != NULL
>>> -      && (__builtin_expect (__sigismember (set, SIGCANCEL), 0)
>>> -      || __builtin_expect (__sigismember (set, SIGSETXID), 0)))
>>> -    {
>>> -      /* Create a temporary mask without the bit for SIGCANCEL set.  */
>>> -      // We are not copying more than we have to.
>>> -      memcpy (&tmpset, set, _NSIG / 8);
>>> -      __sigdelset (&tmpset, SIGCANCEL);
>>> -      __sigdelset (&tmpset, SIGSETXID);
>>> -      set = &tmpset;
>>> -    }
>>> -
>>> -    /* XXX The size argument hopefully will have to be changed to the
>>> -       real size of the user-level sigset_t.  */
>>> +  /* 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, set, info, timeout, _NSIG / 8);
>>>
>>>    /* The kernel generates a SI_TKILL code in si_code in case tkill is
>>>