linux-kernel - Re: [PATCH 2/2] posix-cpu-timers: use ->sighand instead of ->signal to check the task is alive

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]

Date:	Wed, 4 Feb 2009 14:19:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Roland McGrath <roland@...hat.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] posix-cpu-timers: use ->sighand instead of
	->signal to check the task is alive

On 02/04, Peter Zijlstra wrote:
>
> On Wed, 2009-02-04 at 00:17 +0100, Oleg Nesterov wrote:
> > Sadly, it is not trivial to audit kernel/posix-cpu-timers.c, but it really
> > abuses tasklist_lock. I believe it doesn't need this lock at all, but the
> > changes are not easy to test.
>
> It uses that to hold of task reaping so ->signal doesn't go away.

Yes sure, but ->siglock alone is enough (this was not true when this code
was written, as far as I know). It is not trivial to remove tasklist
completely, but some places are trivial.

> If we make ->signal refcountable, and rcu freed along with the tasks I
> think we can get away without tasklist_lock.

I think this is possible even without this change (which is good anyway).
But the problem is not only that ->signal can go away. For example,
posix_cpu_timer_set/posix_cpu_timer_schedule should not proceed if the
task was already released, even if it had the valid ->signal.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/