linux-kernel - [PATCH 11/23] KEYS: fix dereferencing NULL payload with nonzero length

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Date:   Thu, 08 Jun 2017 14:48:40 +0100
From:   David Howells <dhowells@...hat.com>
To:     jmorris@...ei.org
Cc:     Eric Biggers <ebiggers@...gle.com>, linux-kernel@...r.kernel.org,
        dhowells@...hat.com, stable@...r.kernel.org#2.6.10+,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org
Subject: [PATCH 11/23] KEYS: fix dereferencing NULL payload with nonzero
 length

From: Eric Biggers <ebiggers@...gle.com>

sys_add_key() and the KEYCTL_UPDATE operation of sys_keyctl() allowed a
NULL payload with nonzero length to be passed to the key type's
->preparse(), ->instantiate(), and/or ->update() methods.  Various key
types including asymmetric, cifs.idmap, cifs.spnego, and pkcs7_test did
not handle this case, allowing an unprivileged user to trivially cause a
NULL pointer dereference (kernel oops) if one of these key types was
present.  Fix it by doing the copy_from_user() when 'plen' is nonzero
rather than when '_payload' is non-NULL, causing the syscall to fail
with EFAULT as expected when an invalid buffer is specified.

Cc: stable@...r.kernel.org # 2.6.10+
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---

 security/keys/keyctl.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 447a7d5cee0f..94c2790f8283 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -99,7 +99,7 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
 	/* pull the payload in if one was supplied */
 	payload = NULL;
 
-	if (_payload) {
+	if (plen) {
 		ret = -ENOMEM;
 		payload = kvmalloc(plen, GFP_KERNEL);
 		if (!payload)
@@ -324,7 +324,7 @@ long keyctl_update_key(key_serial_t id,
 
 	/* pull the payload in if one was supplied */
 	payload = NULL;
-	if (_payload) {
+	if (plen) {
 		ret = -ENOMEM;
 		payload = kmalloc(plen, GFP_KERNEL);
 		if (!payload)