linux-kernel - Re: [PATCH] ppp_mppe: Don't put InterimKey on the stack

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Message-ID: <46F3D971.2050107@redhat.com>
Date:	Fri, 21 Sep 2007 16:47:13 +0200
From:	Michal Schmidt <mschmidt@...hat.com>
To:	Matt Domsch <Matt_Domsch@...l.com>
CC:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Frank Cusack <fcusack@...sack.com>, linux-ppp@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ppp_mppe: Don't put InterimKey on the stack

Matt Domsch skrev:
> On Fri, Sep 21, 2007 at 04:08:09PM +0200, Michal Schmidt wrote:
>   
>> Hello,
>>
>> The interrupt stack can be in the __START_KERNEL_map region in which
>> virt_to_page will not work. This caused ppp_mppe to crash on CentOS 5 on x86_64
>> (http://bugs.centos.org/view.php?id=2076).
>>
>> The fix is to avoid copying the interim key. We can simply use it in its
>> original place, which is kmalloc'd.
>>     
>
> Needs a Signed-off-by: line, but otherwise, looks good, and even saves
> some stack space.  Thanks for tracking this down.
>
> -Matt
>   

Sorry about the forgotten sign-off. Here it is.
Andrew, please apply.

Signed-off-by: Michal Schmidt <mschmidt@...hat.com>

---
 drivers/net/ppp_mppe.c |   14 ++++++--------
 1 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ppp_mppe.c b/drivers/net/ppp_mppe.c
index f79cf87..c0b6d19 100644
--- a/drivers/net/ppp_mppe.c
+++ b/drivers/net/ppp_mppe.c
@@ -136,7 +136,7 @@ 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 hash_desc desc;
 	struct scatterlist sg[4];
@@ -153,8 +153,6 @@ static void get_new_key_from_sha(struct ppp_mppe_state * state, unsigned char *I
 	desc.flags = 0;
 
 	crypto_hash_digest(&desc, sg, nbytes, state->sha1_digest);
-
-	memcpy(InterimKey, state->sha1_digest, state->keylen);
 }
 
 /*
@@ -163,21 +161,21 @@ 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];
 	struct blkcipher_desc desc = { .tfm = state->arc4 };
 
-	get_new_key_from_sha(state, InterimKey);
+	get_new_key_from_sha(state);
 	if (!initial_key) {
-		crypto_blkcipher_setkey(state->arc4, InterimKey, state->keylen);
-		setup_sg(sg_in, InterimKey, state->keylen);
+		crypto_blkcipher_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_blkcipher_encrypt(&desc, 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 */

-
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