linux-kernel - Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions

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Message-ID: <CAHC9VhQ7ep3HSw8iqWBsiW0hhZ-drVtk7bW1rA1uAyUrbm3PqA@mail.gmail.com>
Date:   Thu, 28 Jun 2018 20:23:02 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>, jannh@...gle.com
Cc:     Eric Paris <eparis@...isplace.org>, selinux@...ho.nsa.gov,
        security@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions

On Tue, Jun 26, 2018 at 8:15 AM Stephen Smalley <sds@...ho.nsa.gov> wrote:
> On 06/25/2018 12:34 PM, Jann Horn wrote:
> > If a user is accessing a file in selinuxfs with a pointer to a userspace
> > buffer that is backed by e.g. a userfaultfd, the userspace access can
> > stall indefinitely, which can block fsi->mutex if it is held.
> >
> > For sel_read_policy(), remove the locking, since this method doesn't seem
> > to access anything that requires locking.
> >
> > For sel_read_bool(), move the user access below the locked region.
> >
> > For sel_write_bool() and sel_commit_bools_write(), move the user access
> > up above the locked region.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Jann Horn <jannh@...gle.com>
>
> Only question I have is wrt the Fixes line, i.e. was this an issue until userfaultfd was introduced, and if not,
> do we need it to be back-ported any further than the commit which introduced it.

Considering we are talking about v2.6.12 I have to wonder if anyone is
bothering with backports for kernels that old.  Even the RHEL-5.x
based systems are at least on v2.6.18.

Regardless, I think this is fine to merge as-is; thanks everyone.

> Otherwise, you can add my
> Acked-by: Stephen Smalley <sds@...ho.nsa.gov>

-- 
paul moore
www.paul-moore.com