linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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: <20110215202747.GA20560@redhat.com>
Date:	Tue, 15 Feb 2011 21:27:47 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
	PTRACE_ATTACH

On 02/15, Roland McGrath wrote:
>
> > Actually I was thinking along this line.  We can allow
> > PTRACE_GETSIGINFO to proceed without forcing the tracee into TRACED
> > state, the rationale being the operation is required to tell between
> > group stop and ptrace trap.  Am I missing something?
>
> The reason for the transition to TASK_TRACED is to prevent a race with
> SIGCONT waking the task.  There is always a race with SIGKILL waking it,
> but the circumstances where that can really matter are far fewer.
> You need to make sure that the work PTRACE_GETSIGINFO does to access
> last_siginfo cannot race with that pointer disappearing or the stack
> space it points to becoming invalid.  I think the use of siglock ensures
> that, but Oleg should verify it.

Yes, I think this is safe.

I do not really like this idea because it looks a bit strange to treat
PTRACE_GETSIGINFO specially, and this doesn't solve all problems. And,
once again, I still hope we can change ptrace_resume() so that it doesn't
wakeup the stopped (I mean, SIGNAL_STOP_STOPPED) tracee, in this case this
hack is not needed.

And. We are going to add the new requests which doesn't need the stopped
tracee anyway. So we can just add PTRACE_HAS_SIGINFO which returns
child->last_siginfo != NULL. This looks simpler, and this is compatible.
Of course this check is racy, but this doesn't matter. PTRACE_GETSIGINFO
is equally racy if it doesn't change the state to TASK_TRACED.

But I won't argue if you/Denys/Tejun prefer to change PTRACE_GETSIGINFO.

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/