linux-kernel - Re: [PATCH] selinux: fix error handling bugs in security_load

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Date:   Wed, 26 Aug 2020 10:47:41 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Eric Paris <eparis@...isplace.org>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Jeff Vander Stoep <jeffv@...gle.com>,
        SElinux list <selinux@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] selinux: fix error handling bugs in security_load_policy()

On Wed, Aug 26, 2020 at 8:49 AM Stephen Smalley
<stephen.smalley.work@...il.com> wrote:
> On Wed, Aug 26, 2020 at 7:32 AM Dan Carpenter <dan.carpenter@...cle.com> wrote:
> >
> > There are a few bugs in the error handling for security_load_policy().
> >
> > 1) If the newpolicy->sidtab allocation fails then it leads to a NULL
> >    dereference.  Also the error code was not set to -ENOMEM on that
> >    path.
> > 2) If policydb_read() failed then we call policydb_destroy() twice
> >    which meands we call kvfree(p->sym_val_to_name[i]) twice.
> > 3) If policydb_load_isids() failed then we call sidtab_destroy() twice
> >    and that results in a double free in the sidtab_destroy_tree()
> >    function because entry.ptr_inner and entry.ptr_leaf are not set to
> >    NULL.
> >
> > One thing that makes this code nice to deal with is that none of the
> > functions return partially allocated data.  In other words, the
> > policydb_read() either allocates everything successfully or it frees
> > all the data it allocates.  It never returns a mix of allocated and
> > not allocated data.
> >
> > I re-wrote this to only free the successfully allocated data which
> > avoids the double frees.  I also re-ordered selinux_policy_free() so
> > it's in the reverse order of the allocation function.
> >
> > Fixes: c7c556f1e81b ("selinux: refactor changing booleans")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>
> I guess this wasn't against current selinux next branch?
>
> patching file security/selinux/ss/services.c
> Hunk #1 succeeded at 2145 (offset 18 lines).
> Hunk #2 succeeded at 2263 (offset 39 lines).
> Hunk #3 succeeded at 2303 with fuzz 1 (offset 47 lines).
> Hunk #4 succeeded at 2323 (offset 42 lines).
>
> But otherwise it looked good to me.
>
> Acked-by: Stephen Smalley <stephen.smalley.work@...il.com>

My guess is that Dan was using selinux/next, just not the latest.

Anyway, the patch is now merged into selinux/next but I had to do some
manual fixes so please double check that it looks okay to you.  Thanks
everyone.

-- 
paul moore
www.paul-moore.com