linux-kernel - Re: [PATCH] signals: work around random wakeups in sigsuspend()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160126211009.GA4695@redhat.com>
Date:	Tue, 26 Jan 2016 22:10:09 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>, linux-kernel@...r.kernel.org,
	mingo@...nel.org, peterz@...radead.org
Subject: Re: [PATCH] signals: work around random wakeups in sigsuspend()

On 01/25, Andrew Morton wrote:
>
> On Mon, 25 Jan 2016 10:21:46 -0500 Sasha Levin <sasha.levin@...cle.com> wrote:
>
> > A random wakeup can get us out of sigsuspend() without TIF_SIGPENDING
> > being set.
> >
> > Avoid that by making sure we were signaled, like sys_pause() does.
>
> What we're lacking here is any description of the end-user-visible
> effects of the bug.

The warning in dmesg and -ERESTARTNOHAND which we should never return to user
space, although I bet nobody checks the error code returned by sigsuspend().

Plus, of course, sys_sigsuspend() can return while it should not.

> Enough for people to be able to decide (and to
> recognize!) whether their kernel needs this patch.</stdrefrain>

I don't think this problem is really serious, plus it is very unlikely. The
spurious return from sigsuspend() should not really hurt.

And, ironically, there is another more serious "reverse" problem ;) sigsuspend()
orany other user of -ERESTARTNOHAND can "miss" the signal, in a sense that the
kernel can wrongly restart this syscall after return from signal handler. This
is not trivial to fix..

Oleg.