linux-stable.git/kernel/signal.c, branch v4.9.44

signal: protect SIGNAL_UNKILLABLE from unintentional clearing.

2017-08-11T15:49:36+00:00

[ Upstream commit 2d39b3cd34e6d323720d4c61bd714f5ae202c022 ]

Since commit 00cd5c37afd5 ("ptrace: permit ptracing of /sbin/init") we
can now trace init processes.  init is initially protected with
SIGNAL_UNKILLABLE which will prevent fatal signals such as SIGSTOP, but
there are a number of paths during tracing where SIGNAL_UNKILLABLE can
be implicitly cleared.

This can result in init becoming stoppable/killable after tracing.  For
example, running:

  while true; do kill -STOP 1; done &
  strace -p 1

and then stopping strace and the kill loop will result in init being
left in state TASK_STOPPED.  Sending SIGCONT to init will resume it, but
init will now respond to future SIGSTOP signals rather than ignoring
them.

Make sure that when setting SIGNAL_STOP_CONTINUED/SIGNAL_STOP_STOPPED
that we don't clear SIGNAL_UNKILLABLE.

Link: http://lkml.kernel.org/r/20170104122017.25047-1-jamie.iles@oracle.com
Signed-off-by: Jamie Iles 
Acked-by: Oleg Nesterov 
Cc: Alexander Viro 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

signal: Only reschedule timers on signals timers have sent

2017-06-29T11:00:29+00:00

commit 57db7e4a2d92c2d3dfbca4ef8057849b2682436b upstream.

Thomas Gleixner  wrote:
> The CRIU support added a 'feature' which allows a user space task to send
> arbitrary (kernel) signals to itself. The changelog says:
>
>   The kernel prevents sending of siginfo with positive si_code, because
>   these codes are reserved for kernel.  I think we can allow a task to
>   send such a siginfo to itself.  This operation should not be dangerous.
>
> Quite contrary to that claim, it turns out that it is outright dangerous
> for signals with info->si_code == SI_TIMER. The following code sequence in
> a user space task allows to crash the kernel:
>
>    id = timer_create(CLOCK_XXX, ..... signo = SIGX);
>    timer_set(id, ....);
>    info->si_signo = SIGX;
>    info->si_code = SI_TIMER:
>    info->_sifields._timer._tid = id;
>    info->_sifields._timer._sys_private = 2;
>    rt_[tg]sigqueueinfo(..., SIGX, info);
>    sigemptyset(&sigset);
>    sigaddset(&sigset, SIGX);
>    rt_sigtimedwait(sigset, info);
>
> For timers based on CLOCK_PROCESS_CPUTIME_ID, CLOCK_THREAD_CPUTIME_ID this
> results in a kernel crash because sigwait() dequeues the signal and the
> dequeue code observes:
>
>   info->si_code == SI_TIMER && info->_sifields._timer._sys_private != 0
>
> which triggers the following callchain:
>
>  do_schedule_next_timer() -> posix_cpu_timer_schedule() -> arm_timer()
>
> arm_timer() executes a list_add() on the timer, which is already armed via
> the timer_set() syscall. That's a double list add which corrupts the posix
> cpu timer list. As a consequence the kernel crashes on the next operation
> touching the posix cpu timer list.
>
> Posix clocks which are internally implemented based on hrtimers are not
> affected by this because hrtimer_start() can handle already armed timers
> nicely, but it's a reliable way to trigger the WARN_ON() in
> hrtimer_forward(), which complains about calling that function on an
> already armed timer.

This problem has existed since the posix timer code was merged into
2.5.63. A few releases earlier in 2.5.60 ptrace gained the ability to
inject not just a signal (which linux has supported since 1.0) but the
full siginfo of a signal.

The core problem is that the code will reschedule in response to
signals getting dequeued not just for signals the timers sent but
for other signals that happen to a si_code of SI_TIMER.

Avoid this confusion by testing to see if the queued signal was
preallocated as all timer signals are preallocated, and so far
only the timer code preallocates signals.

Move the check for if a timer needs to be rescheduled up into
collect_signal where the preallocation check must be performed,
and pass the result back to dequeue_signal where the code reschedules
timers.   This makes it clear why the code cares about preallocated
timers.

Reported-by: Thomas Gleixner 
History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Reference: 66dd34ad31e5 ("signal: allow to send any siginfo to itself")
Reference: 1669ce53e2ff ("Add PTRACE_GETSIGINFO and PTRACE_SETSIGINFO")
Fixes: db8b50ba75f2 ("[PATCH] POSIX clocks & timers")
Signed-off-by: "Eric W. Biederman" 
Signed-off-by: Greg Kroah-Hartman

sigaltstack: support SS_AUTODISARM for CONFIG_COMPAT

2017-03-12T05:41:44+00:00

commit 441398d378f29a5ad6d0fcda07918e54e4961800 upstream.

Currently SS_AUTODISARM is not supported in compatibility mode, but does
not return -EINVAL either.  This makes dosemu built with -m32 on x86_64
to crash.  Also the kernel's sigaltstack selftest fails if compiled with
-m32.

This patch adds the needed support.

Link: http://lkml.kernel.org/r/20170205101213.8163-2-stsp@list.ru
Signed-off-by: Stas Sergeev 
Cc: Milosz Tanski 
Cc: Andy Lutomirski 
Cc: Al Viro 
Cc: Arnd Bergmann 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Oleg Nesterov 
Cc: Nicolas Pitre 
Cc: Waiman Long 
Cc: Dave Hansen 
Cc: Dmitry Safonov 
Cc: Wang Xiaoqiang 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

x86/signal: Add SA_{X32,IA32}_ABI sa_flags

2016-09-14T19:28:11+00:00

Introduce new flags that defines which ABI to use on creating sigframe.
Those flags kernel will set according to sigaction syscall ABI,
which set handler for the signal being delivered.

So that will drop the dependency on TIF_IA32/TIF_X32 flags on signal deliver.
Those flags will be used only under CONFIG_COMPAT.

Similar way ARM uses sa_flags to differ in which mode deliver signal
for 26-bit applications (look at SA_THIRYTWO).

Signed-off-by: Dmitry Safonov 
Reviewed-by: Andy Lutomirski 
Cc: 0x7f454c46@gmail.com
Cc: oleg@redhat.com
Cc: linux-mm@kvack.org
Cc: gorcunov@openvz.org
Cc: xemul@virtuozzo.com
Link: http://lkml.kernel.org/r/20160905133308.28234-7-dsafonov@virtuozzo.com
Signed-off-by: Thomas Gleixner

signals: Use hrtimer for sigtimedwait()

2016-07-07T08:35:07+00:00

We've converted most timeout related syscalls to hrtimers, but
sigtimedwait() did not get this treatment.

Convert it so we get a reasonable accuracy and remove the
user space exposure to the timer wheel properties.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Frederic Weisbecker 
Cc: Al Viro 
Cc: Arjan van de Ven 
Cc: Chris Mason 
Cc: Cyril Hrubis 
Cc: George Spelvin 
Cc: Josh Triplett 
Cc: Len Brown 
Cc: Linus Torvalds 
Cc: Paul McKenney 
Cc: Peter Zijlstra 
Cc: Rik van Riel 
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160704094341.787164909@linutronix.de
Signed-off-by: Ingo Molnar

kernel/signal.c: convert printk(KERN_ ...) to pr_(...)

2016-05-24T00:04:14+00:00

Use pr_ instead of printk(KERN_ ).

Signed-off-by: Wang Xiaoqiang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

signals/sigaltstack: Report current flag bits in sigaltstack()

2016-05-04T06:34:14+00:00

sigaltstack()'s reported previous state uses a somewhat odd
convention, but the concept of flag bits is new, and we can do the
flag bits sensibly.  Specifically, let's just report them directly.

This will allow saving and restoring the sigaltstack state using
sigaltstack() to work correctly.

Signed-off-by: Andy Lutomirski 
Cc: Al Viro 
Cc: Amanieu d'Antras 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Michal Hocko 
Cc: Oleg Nesterov 
Cc: Pavel Emelyanov 
Cc: Peter Zijlstra (Intel) 
Cc: Peter Zijlstra 
Cc: Richard Weinberger 
Cc: Sasha Levin 
Cc: Shuah Khan 
Cc: Stas Sergeev 
Cc: Thomas Gleixner 
Cc: Vladimir Davydov 
Cc: linux-api@vger.kernel.org
Link: http://lkml.kernel.org/r/94b291ec9fd47741a9264851e316e158ded0b00d.1462296606.git.luto@kernel.org
Signed-off-by: Ingo Molnar

signals/sigaltstack: Implement SS_AUTODISARM flag

2016-05-03T06:37:59+00:00

This patch implements the SS_AUTODISARM flag that can be OR-ed with
SS_ONSTACK when forming ss_flags.

When this flag is set, sigaltstack will be disabled when entering
the signal handler; more precisely, after saving sas to uc_stack.
When leaving the signal handler, the sigaltstack is restored by
uc_stack.

When this flag is used, it is safe to switch from sighandler with
swapcontext(). Without this flag, the subsequent signal will corrupt
the state of the switched-away sighandler.

To detect the support of this functionality, one can do:

  err = sigaltstack(SS_DISABLE | SS_AUTODISARM);
  if (err && errno == EINVAL)
	unsupported();

Signed-off-by: Stas Sergeev 
Cc: Al Viro 
Cc: Aleksa Sarai 
Cc: Amanieu d'Antras 
Cc: Andrea Arcangeli 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: Eric W. Biederman 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Heinrich Schuchardt 
Cc: Jason Low 
Cc: Josh Triplett 
Cc: Konstantin Khlebnikov 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Palmer Dabbelt 
Cc: Paul Moore 
Cc: Pavel Emelyanov 
Cc: Peter Zijlstra 
Cc: Richard Weinberger 
Cc: Sasha Levin 
Cc: Shuah Khan 
Cc: Tejun Heo 
Cc: Thomas Gleixner 
Cc: Vladimir Davydov 
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1460665206-13646-4-git-send-email-stsp@list.ru
Signed-off-by: Ingo Molnar

signals/sigaltstack: Prepare to add new SS_xxx flags

2016-05-03T06:37:59+00:00

This patch adds SS_FLAG_BITS - the mask that splits sigaltstack
mode values and bit-flags. Since there is no bit-flags yet, the
mask is defined to 0. The flags are added by subsequent patches.
With every new flag, the mask should have the appropriate bit cleared.

This makes sure if some flag is tried on a kernel that doesn't
support it, the -EINVAL error will be returned, because such a
flag will be treated as an invalid mode rather than the bit-flag.

That way the existence of the particular features can be probed
at run-time.

This change was suggested by Andy Lutomirski:

  https://lkml.org/lkml/2016/3/6/158

Signed-off-by: Stas Sergeev 
Cc: Al Viro 
Cc: Amanieu d'Antras 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Michal Hocko 
Cc: Oleg Nesterov 
Cc: Pavel Emelyanov 
Cc: Peter Zijlstra (Intel) 
Cc: Peter Zijlstra 
Cc: Richard Weinberger 
Cc: Sasha Levin 
Cc: Shuah Khan 
Cc: Thomas Gleixner 
Cc: Vladimir Davydov 
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1460665206-13646-3-git-send-email-stsp@list.ru
Signed-off-by: Ingo Molnar

kernel/signal.c: add compile-time check for __ARCH_SI_PREAMBLE_SIZE

2016-03-22T22:36:02+00:00

The value of __ARCH_SI_PREAMBLE_SIZE defines the size (including
padding) of the part of the struct siginfo that is before the union, and
it is then used to calculate the needed padding (SI_PAD_SIZE) to make
the size of struct siginfo equal to 128 (SI_MAX_SIZE) bytes.

Depending on the target architecture and word width it equals to either
3 or 4 times sizeof int.

Since the very beginning we had __ARCH_SI_PREAMBLE_SIZE wrong on the
parisc architecture for the 64bit kernel build.  It's even more
frustrating, because it can easily be checked at compile time if the
value was defined correctly.

This patch adds such a check for the correctness of
__ARCH_SI_PREAMBLE_SIZE in the hope that it will prevent existing and
future architectures from running into the same problem.

I refrained from replacing __ARCH_SI_PREAMBLE_SIZE by offsetof() in
copy_siginfo() in include/asm-generic/siginfo.h, because a) it doesn't
make any difference and b) it's used in the Documentation/kmemcheck.txt
example.

I ran this patch through the 0-DAY kernel test infrastructure and only
the parisc architecture triggered as expected.  That means that this
patch should be OK for all major architectures.

Signed-off-by: Helge Deller 
Cc: Stephen Rothwell 
Cc: Michael Ellerman 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds