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Re: bash trap ignore signal - race condition


From: Chet Ramey
Subject: Re: bash trap ignore signal - race condition
Date: Tue, 12 Apr 2011 09:30:48 -0400
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2.15) Gecko/20110303 Thunderbird/3.1.9

On 4/12/11 8:33 AM, Roman Rakus wrote:
> There's a race condition when you can hit following:
>       set_signal_handler (sig, SIG_IGN);
>       change_signal (sig, savestring (string));
>       set_signal_handler (sig, trap_handler);
> in trap.c file, set_signal() function.
> So bash set signal to be ignored and then set it to be handled by
> trap_handler. However how should bash behave when the signal is received
> when the trap_handler has been set before. Check the following reproducer:
        [...]
> You can send SIGUSR1 to bash running traploop.sh in the state, when the
> signal is ignored, but shouldn't be. Is there any reason why is the signal
> for short time ignored?

Probably because it's very old code.  That has been there essentially
unchanged since at least bash-1.12 -- almost twenty years ago.  It would
be better to block the signal while the trap string and handler are
being modified.

Chet

> 


-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/



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