From: Mateusz Guzik <mguzik@redhat.com>
To: Richard Guy Briggs <rgb@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
ebiederm@xmission.com, oleg@redhat.com, sgrubb@redhat.com,
pmoore@redhat.com, eparis@redhat.com, luto@amacapital.net,
linux-audit@redhat.com, linux-kernel@vger.kernel.org,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCHv2 0/2] introduce get_task_exe_file and use it to fix audit_exe_compare
Date: Tue, 30 Aug 2016 22:13:28 +0200 [thread overview]
Message-ID: <20160830201327.z5tx3c53co2zwqsx@mguzik> (raw)
In-Reply-To: <20160830185021.GL5983@madcap2.tricolour.ca>
On Tue, Aug 30, 2016 at 02:50:21PM -0400, Richard Guy Briggs wrote:
> On 2016-08-23 16:20, Mateusz Guzik wrote:
> > audit_exe_compare directly accesses mm->exe_file without making sure the
> > object is stable. Fixing it using current primitives results in
> > partially duplicating what proc_exe_link is doing.
> >
> > As such, introduce a trivial helper which can be used in both places and
> > fix the func.
> >
> > Changes since v1:
> > * removed an unused 'out' label which crept in
> >
> > Mateusz Guzik (2):
> > mm: introduce get_task_exe_file
> > audit: fix exe_file access in audit_exe_compare
>
> The task_lock affects a much bigger struct than the mm ref count. Is
> this really necessary? Is a spin-lock significantly lower cost than a
> refcount? Other than that, this refactorization looks sensible.
>
proc_exe_link was taking the lock anyway to guarantee a stable mm.
I think the helper cleans the code up a little bit and there is
microoptimisation to not play with the refcount.
If audit_exe_compare has guarantees the task wont reach exit_mm, it can
use get_mm_exe_file which means the atomic op would be only on the file
object.
I was under the impression this is the expected behaviour, but your
patch used the task lock to grab mm, so I mimicked it here.
--
Mateusz Guzik
prev parent reply other threads:[~2016-08-30 20:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-23 14:20 [PATCHv2 0/2] introduce get_task_exe_file and use it to fix audit_exe_compare Mateusz Guzik
2016-08-23 14:20 ` [PATCHv2 1/2] mm: introduce get_task_exe_file Mateusz Guzik
2016-08-23 14:48 ` Oleg Nesterov
2016-08-23 14:52 ` Mateusz Guzik
2016-08-23 14:20 ` [PATCHv2 2/2] audit: fix exe_file access in audit_exe_compare Mateusz Guzik
2016-08-29 22:50 ` [PATCHv2 0/2] introduce get_task_exe_file and use it to fix audit_exe_compare Paul Moore
2016-08-31 20:22 ` Paul Moore
2016-08-30 18:50 ` Richard Guy Briggs
2016-08-30 20:13 ` Mateusz Guzik [this message]
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