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From:   Paul Moore <paul@paul-moore.com>
Date:   Thu, 28 Jun 2018 20:38:21 -0400
Message-ID: <CAHC9VhTcncUn3CgAgG-FiXyyoNiq5DdHF1cSYJeWpu8PvRXucw@mail.gmail.com>
Subject: Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions
To:     jannh@google.com
Cc:     Eric Paris <eparis@parisplace.org>, selinux@tycho.nsa.gov,
        security@kernel.org, linux-kernel@vger.kernel.org,
        Stephen Smalley <sds@tycho.nsa.gov>
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On Thu, Jun 28, 2018 at 8:23 PM Paul Moore <paul@paul-moore.com> wrote:
> On Tue, Jun 26, 2018 at 8:15 AM Stephen Smalley <sds@tycho.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@vger.kernel.org
> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > Signed-off-by: Jann Horn <jannh@google.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.

FYI, I did have to remove the "fsi" variable from sel_read_policy() to
keep the compiler happy.  Please double check to make sure your code
compiles cleanly in the future.

-- 
paul moore
www.paul-moore.com