From: Michal Schmidt <mschmidt@redhat.com>
Date: Wed, 10 Oct 2007 09:53:02 +0200
Subject: [net] ppp_mppe: avoid using a copy of interim key
Message-id: 470C84DE.600@redhat.com
O-Subject: [RHEL5.2 PATCH] ppp_mppe: kernel panic on x86_64
Bugzilla: 248716

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=248716

Starting a PPTP connection (on a server with pptpd or on a client with
pptpclient) on x86_64 results in a kernel panic. The problem is
mppe_rekey runs in interrupt context and it uses virt_to_page on its
stack-allocated buffer InterimKey. Doing virt_to_XXX on a kernel stack
is a bug.

The fix is to avoid copying the interim key to the stack. We can simply
use it in its original place, which is kmalloc'd. This even saves some
stack space.

Successfully tested by the reporter and by myself.

The patch is upstream since v2.6.23-rc9 and it's being considered for
2.6.22.10 too.

Michal

Acked-by: "David S. Miller" <davem@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Herbert Xu <herbert.xu@redhat.com>

diff --git a/drivers/net/ppp_mppe.c b/drivers/net/ppp_mppe.c
index 51ff9a9..bf6f877 100644
--- a/drivers/net/ppp_mppe.c
+++ b/drivers/net/ppp_mppe.c
@@ -134,7 +134,7 @@ struct ppp_mppe_state {
  * Key Derivation, from RFC 3078, RFC 3079.
  * Equivalent to Get_Key() for MS-CHAP as described in RFC 3079.
  */
-static void get_new_key_from_sha(struct ppp_mppe_state * state, unsigned char *InterimKey)
+static void get_new_key_from_sha(struct ppp_mppe_state * state)
 {
 	struct scatterlist sg[4];
 
@@ -144,8 +144,6 @@ static void get_new_key_from_sha(struct ppp_mppe_state * state, unsigned char *I
 	setup_sg(&sg[3], sha_pad->sha_pad2, sizeof(sha_pad->sha_pad2));
 
 	crypto_digest_digest (state->sha1, sg, 4, state->sha1_digest);
-
-	memcpy(InterimKey, state->sha1_digest, state->keylen);
 }
 
 /*
@@ -154,20 +152,20 @@ static void get_new_key_from_sha(struct ppp_mppe_state * state, unsigned char *I
  */
 static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
 {
-	unsigned char InterimKey[MPPE_MAX_KEY_LEN];
 	struct scatterlist sg_in[1], sg_out[1];
 
-	get_new_key_from_sha(state, InterimKey);
+	get_new_key_from_sha(state);
 	if (!initial_key) {
-		crypto_cipher_setkey(state->arc4, InterimKey, state->keylen);
-		setup_sg(sg_in, InterimKey, state->keylen);
+		crypto_cipher_setkey(state->arc4, state->sha1_digest,
+				     state->keylen);
+		setup_sg(sg_in, state->sha1_digest, state->keylen);
 		setup_sg(sg_out, state->session_key, state->keylen);
 		if (crypto_cipher_encrypt(state->arc4, sg_out, sg_in,
 				      state->keylen) != 0) {
     		    printk(KERN_WARNING "mppe_rekey: cipher_encrypt failed\n");
 		}
 	} else {
-		memcpy(state->session_key, InterimKey, state->keylen);
+		memcpy(state->session_key, state->sha1_digest, state->keylen);
 	}
 	if (state->keylen == 8) {
 		/* See RFC 3078 */