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

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Date:   Wed, 16 Oct 2019 20:46:18 -0500
From:   Navid Emamdoost <navid.emamdoost@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     emamd001@....edu, smccaman@....edu, kjlu@....edu,
        Navid Emamdoost <navid.emamdoost@...il.com>,
        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: [PATCH] apparmor: Fix use-after-free in aa_audit_rule_init

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 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.

Fixes: 52e8c38001d8 ("apparmor: Fix memory leak of rule on error exit path")
Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
---
 security/apparmor/audit.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/security/apparmor/audit.c b/security/apparmor/audit.c
index 5a98661a8b46..48c15fb0aafe 100644
--- a/security/apparmor/audit.c
+++ b/security/apparmor/audit.c
@@ -178,6 +178,7 @@ void aa_audit_rule_free(void *vrule)
 int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
 {
 	struct aa_audit_rule *rule;
+	int err;
 
 	switch (field) {
 	case AUDIT_SUBJ_ROLE:
@@ -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;
 		aa_audit_rule_free(rule);
-		return PTR_ERR(rule->label);
+		return PTR_ERR(err);
 	}
 
 	*vrule = rule;
-- 
2.17.1