Re: [PATCH 4/4] signal: Only handle on NSIG signals on signal functions (BZ #25657)

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 21/04/2020 09:53, Florian Weimer wrote:
> * Adhemerval Zanella via Libc-alpha:
> 
>> The upper bits of the sigset_t s not fully initialized in the signal
>> mask calls that return information from kernel (sigprocmask,
>> sigpending, and pthread_sigmask), since the exported sigset_t size
>> (1024 bits) is larger than Linux support one (64 or 128 bits).
>> It might make sigisemptyset/sigorset/sigandset fail if the mask
>> is filled prior the call.
>>
>> This patch changes the internal signal function to handle up to
>> supported Linux signal number (_NSIG), the remaining bits are
>> untouched.
> 
> Sorry, I have trouble what the intended outcome of this change is.
> 
> What is the expected behavior here?  We have an overly large sigset_t,
> but only signal numbers from 0 to NSIG - 1 (inclusive) are valid in
> all function calls?
> 

The bug report link to a stackoverflow example, which simplified is:

  #define _GNU_SOURCE
  #include <stdio.h>
  #include <signal.h>
  int
  main (int argc, char *argv[])
  { 
    sigset_t set;
    sigfillset (&set);
    sigprocmask (SIG_BLOCK, NULL, &set);
    printf ("%d\n", sigisemptyset (&set));
   return 0;
  }

The main issue is GNU extensions sigisemptyset/sigorset/sigandset
operates on full internal signal bits where kernel only updates
up to _NSIG signals.