Re: [PATCH] apparmor: Fix use-after-free in aa_audit_rule_init

From: Navid Emamdoost <navid.emamdoost@gmail.com>
To: John Johansen <john.johansen@canonical.com>
Cc: Markus Elfring <Markus.Elfring@web.de>,
	linux-security-module@vger.kernel.org,
	kernel-janitors@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Navid Emamdoost <emamd001@umn.edu>, Kangjie Lu <kjlu@umn.edu>,
	Stephen McCamant <smccaman@umn.edu>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Tyler Hicks <tyhicks@canonical.com>
Subject: Re: [PATCH] apparmor: Fix use-after-free in aa_audit_rule_init
Date: Mon, 21 Oct 2019 10:25:41 -0500	[thread overview]
Message-ID: <CAEkB2EQgv9_niKU0dagjZH-wRoHc=6+X4O7nGoVbaz9LWPwy6g@mail.gmail.com> (raw)
In-Reply-To: <57b61298-cbeb-f0ff-c6ba-b8f64d5d0287@canonical.com>

On Sun, Oct 20, 2019 at 1:51 PM John Johansen
<john.johansen@canonical.com> wrote:
>
> On 10/20/19 7:16 AM, Markus Elfring wrote:
> >> … But after this release the the return statement
> >> tries to access the label field of the rule which results in
> >> use-after-free. Before releaseing the rule, copy errNo and return it
> >> after releasing rule.
> >
> Navid thanks for finding this, and Markus thanks for the review
>
> > Please avoid a duplicate word and a typo in this change description.
> > My preference would be a v2 version of the patch with the small clean-ups
> that Markus has pointed out.

John and Markus, I updated and submitted v2.

>
> If I don't see a v2 this week I can pull this one in and do the revisions
> myself adding a little fix-up note.
>
> >
> > …
> >> +++ b/security/apparmor/audit.c
> > …
> >> @@ -197,8 +198,9 @@ int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
> >>      rule->label = aa_label_parse(&root_ns->unconfined->label, rulestr,
> >>                                   GFP_KERNEL, true, false);
> >>      if (IS_ERR(rule->label)) {
> >> +            err = rule->label;
> >
> > How do you think about to define the added local variable in this if branch directly?
> >
> > +             int err = rule->label;
> >
>
> yes, since err isn't defined or in use else where this would be preferable
>
> >>              aa_audit_rule_free(rule);
> >> -            return PTR_ERR(rule->label);
> >> +            return PTR_ERR(err);
> >>      }
> >>
> >>      *vrule = rule;
> >
> >
> > Regards,
> > Markus
> >
>

-- 
Thanks,
Navid.