Re: [PATCH 1/2] SELinux: Fix lsm_get_self_attr()

From: Paul Moore <paul@paul-moore.com>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: Casey Schaufler <casey@schaufler-ca.com>,
	John Johansen <john.johansen@canonical.com>,
	 James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	linux-kernel@vger.kernel.org,
	 linux-security-module@vger.kernel.org, stable@vger.kernel.org,
	 selinux@vger.kernel.org
Subject: Re: [PATCH 1/2] SELinux: Fix lsm_get_self_attr()
Date: Fri, 23 Feb 2024 16:05:16 -0500	[thread overview]
Message-ID: <CAHC9VhRdRK3FztE-Th=3M+0ZjCZQJ+5sTiXPwfK6xXX_=SFHhA@mail.gmail.com> (raw)
In-Reply-To: <20240223.eij0Oudai0Ia@digikod.net>

On Fri, Feb 23, 2024 at 3:04 PM Mickaël Salaün <mic@digikod.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
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."

-- 
paul-moore.com