linux-kernel - Re: [PATCH 1/2] SELinux: Fix lsm_get_self

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Message-ID: <20240223.goo9Xei0xa9S@digikod.net>
Date: Fri, 23 Feb 2024 23:03:27 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Paul Moore <paul@...l-moore.com>
Cc: Casey Schaufler <casey@...aufler-ca.com>, 
	John Johansen <john.johansen@...onical.com>, James Morris <jmorris@...ei.org>, 
	"Serge E . Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org, 
	linux-security-module@...r.kernel.org, stable@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH 1/2] SELinux: Fix lsm_get_self_attr()

On Fri, Feb 23, 2024 at 04:05:16PM -0500, Paul Moore wrote:
> On Fri, Feb 23, 2024 at 3:04 PM Mickaël Salaün <mic@...ikod.net> wrote:
> >
> > On Fri, Feb 23, 2024 at 08:59:34PM +0100, Mickaël Salaün wrote:
> > > On Fri, Feb 23, 2024 at 08:05:45PM +0100, Mickaël Salaün wrote:
> > > > selinux_lsm_getattr() may not initialize the value's pointer in some
> > > > case.  As for proc_pid_attr_read(), initialize this pointer to NULL in
> > > > selinux_getselfattr() to avoid an UAF in the kfree() call.
> > >
> > > Not UAF but NULL pointer dereference (both patches)...
> >
> > Well, that may be the result (as observed with the kfree() call), but
> > the cause is obviously an uninitialized pointer.
> 
> Adding the SELinux list to the CC line; SELinux folks the original post is here:
> 
> * https://lore.kernel.org/all/20240223190546.3329966-1-mic@digikod.net
> 
> Thanks for finding this and testing the patch, based on our off-list
> discussion, do you mind if I add a Suggested-by?  Looking at this a

Sure! I was in a hurry and didn't give it the attention it needed...

> bit more I think we'll want to make a few changes to
> selinux_lsm_getattr() later, but this patch is a good one for stable
> as it not only fixes the bug, but it is a trivial one-liner with very
> low risk.
> 
> I do think we need to tweak the commit description a bit, what do you
> think of the following?
> 
>   "selinux_getselfattr() doesn't properly initialize the string
>    pointer it passes to selinux_lsm_getattr() which can cause a
>    problem when an attribute hasn't been explicitly set;
>    selinux_lsm_getattr() returns 0/success, but does not set or
>    initialize the string label/attribute.  Failure to properly
>    initialize the string causes problems later in
>    selinux_getselfattr() when the function attempts to kfree()
>    the string."

Much better!