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Re: SIGTERM ignored before exec race

From: Pádraig Brady
Subject: Re: SIGTERM ignored before exec race
Date: Mon, 11 Feb 2013 22:38:46 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1

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

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
signal (SIGTERM, SIG_IGN);    // continue to ignore TERM
sigprocmask(sigterm_unblock); // reset


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