linux-kernel - Re: [PATCH v3] apparmor: Fix use-after-free in aa_audit_rule

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Date:   Mon, 21 Oct 2019 11:08:14 -0500
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Navid Emamdoost <navid.emamdoost@...il.com>
Cc:     emamd001@....edu, smccaman@....edu, kjlu@....edu,
        John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] apparmor: Fix use-after-free in aa_audit_rule_init

On 2019-10-21 11:05:31, 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")
> Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>

Reviewed-by: Tyler Hicks <tyhicks@...onical.com>

Thanks!

Tyler

> ---
> Changes in v3:
> 	-- applied Tyler Hicks recommendation on err initialization.
> 
>  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..597732503815 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 = PTR_ERR(rule->label);
>  		aa_audit_rule_free(rule);
> -		return PTR_ERR(rule->label);
> +		return err;
>  	}
>  
>  	*vrule = rule;
> -- 
> 2.17.1
>