Re: SIGTERM ignored before exec race

[Pádraig Brady]

On 02/10/2013 08:30 PM, Chet Ramey wrote:
> On 2/9/13 12:02 AM, Pádraig Brady wrote:
> > $ rpm -q kernel glibc bash
> > kernel-2.6.40.4-5.fc15.x86_64
> > glibc-2.14.1-6.x86_64
> > bash-4.2.10-4.fc15.x86_64
> >
> > I notice the following will wait for 5 seconds for
> > the timeout process to end with SIGALRM, rather than
> > immediately due to kill sending the SIGTERM.
>
> I'll take a look at making the race window smaller; there is probably
> some code reordering that will have a beneficial effect.
>
> This race exists, to a certain extent, in all Bourne-like shells.  This
> problem only happens when run interactively, and it happens because
> interactive shells ignore SIGTERM.  No matter how quickly you modify a
> child's signal handlers after fork() returns, there's always the chance
> that a kernel's scheduling policies or aome global auto-nice of child
> or background processes will cause it to happen.

You might be able to do something like:

sigprocmask(sigterm_block);   // ensure parent shell doesn't get TERM
signal (SIGTERM, SIG_DFL);    // reset to default for child to inherit
fork();
signal (SIGTERM, SIG_IGN);    // continue to ignore TERM
sigprocmask(sigterm_unblock); // reset

cheers,
Pádraig.