[PATCH v3] apparmor: Fix use-after-free in aa_audit_rule_init

From: Navid Emamdoost <navid.emamdoost@gmail.com>
To: tyhicks@canonical.com
Cc: emamd001@umn.edu, smccaman@umn.edu, kjlu@umn.edu,
	Navid Emamdoost <navid.emamdoost@gmail.com>,
	John Johansen <john.johansen@canonical.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v3] apparmor: Fix use-after-free in aa_audit_rule_init
Date: Mon, 21 Oct 2019 11:05:31 -0500	[thread overview]
Message-ID: <20191021160532.7719-1-navid.emamdoost@gmail.com> (raw)
In-Reply-To: <20191021154533.GB12140@elm>

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@gmail.com>
---
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

