Bug#571639: libc6: pthread_cancel dies screaming if passed an uninitialised pthread_t

[Ron <ron@debian.org>]

Package: libc6
Version: 2.10.2-5
Severity: normal

Hi,

If the equivalent of this happens, then pthread_cancel segfaults:

static pthread_t p;
int main(void)
{
	pthread_cancel(p);
}


Culprit would appear to be in pthread_cancel.c:

  /* Make sure the descriptor is valid.  */
  if (INVALID_TD_P (pd))
    /* Not a valid thread handle.  */
    return ESRCH;

Which expands in nptl/pthreadP.h to:
# define INVALID_TD_P(pd) __builtin_expect ((pd)->tid <= 0, 0)

and Kaboom QED.


SuS would appear to allow us to explode with an 'uninitialised' pthread_t,
or at least doesn't expressly forbid it anywhere I can see, but it would
seem better if we still didn't with a 'default initialised' variable.

I don't really expect this to work in compliant code, so I won't object
if you wontfix or close it, but it surprised me enough to look and point.

Cheers,
Ron