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From: Florian Weimer <fweimer@redhat.com>
To: Rich Felker <dalias@libc.org>
Cc: musl@lists.openwall.com,
	 Carlos O'Donell via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [musl] Re: [PATCH] Make abort() AS-safe (Bug 26275).
Date: Thu, 01 Oct 2020 17:11:19 +0200	[thread overview]
Message-ID: <87o8lmhtgo.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20201001143918.GN17637@brightrain.aerifal.cx> (Rich Felker's message of "Thu, 1 Oct 2020 10:39:19 -0400")

* Rich Felker:

> On Thu, Oct 01, 2020 at 08:08:24AM +0200, Florian Weimer wrote:
>> * Rich Felker:
>> 
>> > Even without fork, execve and posix_spawn can also see the SIGABRT
>> > disposition change made by abort(), passing it on to a process that
>> > should have started with a disposition of SIG_IGN if you hit exactly
>> > the wrong spot in the race.
>> 
>> My feeling is that it's not worth bothering with this kind of leakage.
>> We've had this bug forever in glibc, and no one has complained about
>> it.
>> 
>> Carlos is investigating removal of the abort lock from glibc, I think.
>
> I don't think that's a good solution. The lock is really important in
> that it protects against serious wrong behavior *within the process*
> like an application-installed signal handler for SIGABRT getting
> called more than once.

I think glibc currently has this bug.  We only avoid it for abort, but
I'm not sure if it's a bug to handle the handler multiple times if abort
is called more than once.

But even for the more general case (threads call sigaction to install a
SIGABRT handler): Do we actually need a lock there?  We reach this state
only after raise (SIGABRT) has returned.  At this point, we can set a
flag (not a lock), and every other thread that calls signal or sigaction
would instead perform the late-stage SIG_DFL-for-SIGABRT part of abort?
It probably still needs some fiddling with sigprocmask.

Thanks,
Florian
-- 
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  reply	other threads:[~2020-10-01 15:12 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200927141952.121047-1-carlos@redhat.com>
     [not found] ` <871rinm1fx.fsf@mid.deneb.enyo.de>
     [not found]   ` <20200928234833.GC17637@brightrain.aerifal.cx>
     [not found]     ` <87d025jcn0.fsf@mid.deneb.enyo.de>
     [not found]       ` <20200929144207.GD17637@brightrain.aerifal.cx>
2020-10-01  2:30         ` Rich Felker
2020-10-01  6:08           ` Florian Weimer
2020-10-01 14:39             ` Rich Felker
2020-10-01 15:11               ` Florian Weimer [this message]
2020-10-01 15:28                 ` Rich Felker
2020-10-01 14:49             ` Carlos O'Donell
2020-10-01 14:55               ` Rich Felker
2020-10-10  0:26           ` Rich Felker

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