Re: [PATCH v2] apparmor: Fix use-after-free in aa_audit_rule_init

From: Tyler Hicks <tyhicks@canonical.com>
To: Navid Emamdoost <navid.emamdoost@gmail.com>
Cc: john.johansen@canonical.com, emamd001@umn.edu, smccaman@umn.edu,
	kjlu@umn.edu, James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] apparmor: Fix use-after-free in aa_audit_rule_init
Date: Mon, 21 Oct 2019 10:45:34 -0500	[thread overview]
Message-ID: <20191021154533.GB12140@elm> (raw)
In-Reply-To: <20191021152348.3906-1-navid.emamdoost@gmail.com>

On 2019-10-21 10:23:47, Navid Emamdoost wrote:
> In the implementation of aa_audit_rule_init(), when aa_label_parse()
> fails the allocated memory for rule is released using
> aa_audit_rule_free(). But after this release, the return statement
> tries to access the label field of the rule which results in
> use-after-free. Before releasing the rule, copy errNo and return it
> after release.
> 
> Fixes: 52e8c38001d8 ("apparmor: Fix memory leak of rule on error exit path")

Ugh! I'm not sure what I was thinking when I authored that patch. :/

> Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
> ---
> Changes in v2:
> 	-- Fix typo in description
> 	-- move err definition inside the if statement.
> 
>  security/apparmor/audit.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/apparmor/audit.c b/security/apparmor/audit.c
> index 5a98661a8b46..334065302fb6 100644
> --- a/security/apparmor/audit.c
> +++ b/security/apparmor/audit.c
> @@ -197,8 +197,9 @@ 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)) {
> +		int err = rule->label;

Since rule->label is a pointer, I'd like to see this:

 int err = PTR_ERR(rule->label);

>  		aa_audit_rule_free(rule);
> -		return PTR_ERR(rule->label);
> +		return PTR_ERR(err);

This line would change to:

 return err;

Tyler

>  	}
>  
>  	*vrule = rule;
> -- 
> 2.17.1
> 