linux-kernel - Re: [PATCH] apparmor: Fix use-after-free in aa_audit_rule

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Message-ID: <57b61298-cbeb-f0ff-c6ba-b8f64d5d0287@canonical.com>
Date:   Sun, 20 Oct 2019 11:49:38 -0700
From:   John Johansen <john.johansen@...onical.com>
To:     Markus Elfring <Markus.Elfring@....de>,
        Navid Emamdoost <navid.emamdoost@...il.com>,
        linux-security-module@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        Navid Emamdoost <emamd001@....edu>, Kangjie Lu <kjlu@....edu>,
        Stephen McCamant <smccaman@....edu>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Tyler Hicks <tyhicks@...onical.com>
Subject: Re: [PATCH] apparmor: Fix use-after-free in aa_audit_rule_init

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.

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
>