Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions
On Thu, Jun 28, 2018 at 8:38 PM Paul Moore wrote:
> On Thu, Jun 28, 2018 at 8:23 PM Paul Moore wrote:
> > On Tue, Jun 26, 2018 at 8:15 AM Stephen Smalley 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: sta...@vger.kernel.org
> > > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > > Signed-off-by: Jann Horn
> > >
> > > 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.
I realize I didn't specify this above ... I merged this into
selinux/stable-4.18; I'm building a test kernel now and if everything
looks okay I'll send it to Linus tomorrow.
--
paul moore
www.paul-moore.com
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Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions
On Thu, Jun 28, 2018 at 8:23 PM Paul Moore wrote:
> On Tue, Jun 26, 2018 at 8:15 AM Stephen Smalley 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: sta...@vger.kernel.org
> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > Signed-off-by: Jann Horn
> >
> > 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
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Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions
On Tue, Jun 26, 2018 at 8:15 AM Stephen Smalley 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: sta...@vger.kernel.org
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Jann Horn
>
> 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
--
paul moore
www.paul-moore.com
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Re: [PATCH] selinux: move user accesses in selinuxfs out of locked regions
On Mon, Jun 25, 2018 at 6:40 PM Jann Horn wrote: > > On Tue, Jun 26, 2018 at 12:36 AM Paul Moore wrote: > > > > On Mon, Jun 25, 2018 at 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. > > > > Forgive me, I'm thinking about this quickly so I could be very wrong > > here, but isn't the mutex needed to prevent problems in multi-threaded > > apps hitting the same fd at the same time? > > sel_read_policy() operates on a read-only copy of the policy, accessed > via ->private_data, allocated using vmalloc in sel_open_policy() via > security_read_policy(). As far as I can tell, nothing can write to > that read-only copy of the policy. None of the handlers in > sel_policy_ops write - they just mmap as readonly (in which case > you're already reading without locks, by the way) or read. Great, thanks. -- paul moore www.paul-moore.com ___ Selinux mailing list Selinux@tycho.nsa.gov To unsubscribe, send email to selinux-le...@tycho.nsa.gov. To get help, send an email containing "help" to selinux-requ...@tycho.nsa.gov.
