linux-kernel - [PATCH v2] audit: fix potential null dereference 'context->module.name'

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Date:   Wed, 25 Jul 2018 10:26:19 +0800
From:   Yi Wang <wang.yi59@....com.cn>
To:     paul@...l-moore.com
Cc:     eparis@...hat.com, linux-audit@...hat.com,
        linux-kernel@...r.kernel.org, jiang.biao2@....com.cn,
        wang.yi59@....com.cn, zhong.weidong@....com.cn
Subject: [PATCH v2] audit: fix potential null dereference 'context->module.name'

The variable 'context->module.name' may be null pointer when
kmalloc return null, so it's better to check it before using
to avoid null dereference.
Another one more thing this patch does is using kstrdup instead
of (kmalloc + strcpy), and signal a lost record via audit_log_lost.

Signed-off-by: Yi Wang <wang.yi59@....com.cn>
Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>
---
v2: use kstrdup instead of kmalloc + strcpy, and signal a lost
record. Thanks to Eric and Paul.

 kernel/auditsc.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index e80459f..713386a 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1272,8 +1272,12 @@ static void show_special(struct audit_context *context, int *call_panic)
 		break;
 	case AUDIT_KERN_MODULE:
 		audit_log_format(ab, "name=");
-		audit_log_untrustedstring(ab, context->module.name);
-		kfree(context->module.name);
+		if (context->module.name) {
+			audit_log_untrustedstring(ab, context->module.name);
+			kfree(context->module.name);
+		} else
+			audit_log_format(ab, "(null)");
+
 		break;
 	}
 	audit_log_end(ab);
@@ -2408,8 +2412,9 @@ void __audit_log_kern_module(char *name)
 {
 	struct audit_context *context = current->audit_context;
 
-	context->module.name = kmalloc(strlen(name) + 1, GFP_KERNEL);
-	strcpy(context->module.name, name);
+	context->module.name = kstrdup(name, GFP_KERNEL);
+	if (!context->module.name)
+		audit_log_lost("out of memory in __audit_log_kern_module");
 	context->type = AUDIT_KERN_MODULE;
 }
 
-- 
1.8.3.1