linux-kernel - [PATCH] CRED: Fix double free in prepare_usermodehelper

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Message-ID: <20100420214117.10400.82534.stgit@warthog.procyon.org.uk>
Date:	Tue, 20 Apr 2010 22:41:18 +0100
From:	David Howells <dhowells@...hat.com>
To:	linux-security-module@...r.kernel.org
Cc:	dhowells@...hat.com, mathieu.desnoyers@...icios.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH] CRED: Fix double free in prepare_usermodehelper_creds() error
	handling

Patch 570b8fb505896e007fd3bb07573ba6640e51851d:

	Author: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
	Date:   Tue Mar 30 00:04:00 2010 +0100
	Subject: CRED: Fix memory leak in error handling

attempts to fix a memory leak in the error handling by making the offending
return statement into a jump down to the bottom of the function where a
kfree(tgcred) is inserted.

This is, however, incorrect, as it does a kfree() after doing put_cred() if
security_prepare_creds() fails.  That will result in a double free if 'error'
is jumped to as put_cred() will also attempt to free the new tgcred record by
virtue of it being pointed to by the new cred record.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 kernel/cred.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/cred.c b/kernel/cred.c
index e1dbe9e..ce1a52b 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -398,6 +398,8 @@ struct cred *prepare_usermodehelper_creds(void)
 
 error:
 	put_cred(new);
+	return NULL;
+
 free_tgcred:
 #ifdef CONFIG_KEYS
 	kfree(tgcred);

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