linux-kernel - [PATCH 3.16 156/178] KEYS: Change the name of the dead type to ".dead" to prevent user access

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Message-ID: <lsq.1500213406.95919901@decadent.org.uk>
Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David Howells" <dhowells@...hat.com>
Subject: [PATCH 3.16 156/178] KEYS: Change the name of the dead type to
 ".dead" to prevent user access

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells@...hat.com>

commit c1644fe041ebaf6519f6809146a77c3ead9193af upstream.

This fixes CVE-2017-6951.

Userspace should not be able to do things with the "dead" key type as it
doesn't have some of the helper functions set upon it that the kernel
needs.  Attempting to use it may cause the kernel to crash.

Fix this by changing the name of the type to ".dead" so that it's rejected
up front on userspace syscalls by key_get_type_from_user().

Though this doesn't seem to affect recent kernels, it does affect older
ones, certainly those prior to:

	commit c06cfb08b88dfbe13be44a69ae2fdc3a7c902d81
	Author: David Howells <dhowells@...hat.com>
	Date:   Tue Sep 16 17:36:06 2014 +0100
	KEYS: Remove key_type::match in favour of overriding default by match_preparse

which went in before 3.18-rc1.

Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 security/keys/gc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -46,7 +46,7 @@ static unsigned long key_gc_flags;
  * immediately unlinked.
  */
 struct key_type key_type_dead = {
-	.name = "dead",
+	.name = ".dead",
 };

 /*