linux-kernel - Re: [PATCH] copy_process(): Move fd_install() out of sighand->siglock critical section

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: <YgK/fdYWi0wWysci@zeniv-ca.linux.org.uk>
Date:   Tue, 8 Feb 2022 19:07:41 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Waiman Long <longman@...hat.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexey Gladkov <legion@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jann Horn <jannh@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] copy_process(): Move fd_install() out of
 sighand->siglock critical section

On Tue, Feb 08, 2022 at 01:51:35PM -0500, Waiman Long wrote:
> On 2/8/22 13:16, Al Viro wrote:
> > On Tue, Feb 08, 2022 at 11:39:12AM -0500, Waiman Long wrote:
> > 
> > > One way to solve this problem is to move the fd_install() call out of
> > > the sighand->siglock critical section.
> > > 
> > > Before commit 6fd2fe494b17 ("copy_process(): don't use ksys_close()
> > > on cleanups"), the pidfd installation was done without holding both
> > > the task_list lock and the sighand->siglock. Obviously, holding these
> > > two locks are not really needed to protect the fd_install() call.
> > > So move the fd_install() call down to after the releases of both locks.
> > 	Umm... That assumes we can delay it that far.  IOW, that nothing
> > relies upon having pidfd observable in /proc/*/fd as soon as the child
> > becomes visible there in the first place.
> > 
> > 	What warranties are expected from CLONE_PIDFD wrt observation of
> > child's descriptor table?
> > 
> I think the fd_install() call can be moved after the release of
> sighand->siglock but before the release the tasklist_lock. Will that be good
> enough?

Looks like it should, but I'd rather hear from the CLONE_PIDFD authors first...
Christian, could you comment on that?