[PPP]: add PPP MPPE encryption module

From: Matt Domsch <Matt_Domsch@dell.com>

The patch below implements the Microsoft Point-to-Point Encryption method
as a PPP compressor/decompressor.  This is necessary for Linux clients and
servers to interoperate with Microsoft Point-to-Point Tunneling Protocol
(PPTP) servers (either Microsoft PPTP servers or the poptop project) which
use MPPE to encrypt data when creating a VPN.

This patch differs from the kernel_ppp_mppe DKMS pacakge at
pptpclient.sourceforge.net by utilizing the kernel crypto routines rather
than providing its own SHA1 and arcfour implementations.

Minor changes to ppp_generic.c try to prevent a link from disabling
compression (in our case, the encryption) after it has started using
compression (encryption).

Feedback to <pptpclient-devel@lists.sourceforge.net> please.

Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>
Cc: James Cameron <james.cameron@hp.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Brice Goglin <Brice.Goglin@ens-lyon.org>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 888 insertions, 24 deletions

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 1958d9e16a3a..24f1691b84f9 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -2523,6 +2523,19 @@ config PPP_BSDCOMP
 	  module; it is called bsd_comp and will show up in the directory
 	  modules once you have said "make modules". If unsure, say N.
 
+config PPP_MPPE
+       tristate "PPP MPPE compression (encryption) (EXPERIMENTAL)"
+       depends on PPP && EXPERIMENTAL
+       select CRYPTO
+       select CRYPTO_SHA1
+       select CRYPTO_ARC4
+       ---help---
+         Support for the MPPE Encryption protocol, as employed by the
+	 Microsoft Point-to-Point Tunneling Protocol.
+
+	 See http://pptpclient.sourceforge.net/ for information on
+	 configuring PPTP clients and servers to utilize this method.
+
 config PPPOE
 	tristate "PPP over Ethernet (EXPERIMENTAL)"
 	depends on EXPERIMENTAL && PPP
diff --git a/drivers/net/Makefile b/drivers/net/Makefile
index 7c313cb341b8..4cffd34442aa 100644
--- a/drivers/net/Makefile
+++ b/drivers/net/Makefile
@@ -112,6 +112,7 @@ obj-$(CONFIG_PPP_ASYNC) += ppp_async.o
 obj-$(CONFIG_PPP_SYNC_TTY) += ppp_synctty.o
 obj-$(CONFIG_PPP_DEFLATE) += ppp_deflate.o
 obj-$(CONFIG_PPP_BSDCOMP) += bsd_comp.o
+obj-$(CONFIG_PPP_MPPE) += ppp_mppe.o
 obj-$(CONFIG_PPPOE) += pppox.o pppoe.o
 
 obj-$(CONFIG_SLIP) += slip.o
diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index d3c9958b00d0..50430f79f8cf 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -137,13 +137,14 @@ struct ppp {
 
 /*
  * Bits in flags: SC_NO_TCP_CCID, SC_CCP_OPEN, SC_CCP_UP, SC_LOOP_TRAFFIC,
- * SC_MULTILINK, SC_MP_SHORTSEQ, SC_MP_XSHORTSEQ, SC_COMP_TCP, SC_REJ_COMP_TCP.
+ * SC_MULTILINK, SC_MP_SHORTSEQ, SC_MP_XSHORTSEQ, SC_COMP_TCP, SC_REJ_COMP_TCP,
+ * SC_MUST_COMP
  * Bits in rstate: SC_DECOMP_RUN, SC_DC_ERROR, SC_DC_FERROR.
  * Bits in xstate: SC_COMP_RUN
  */
 #define SC_FLAG_BITS	(SC_NO_TCP_CCID|SC_CCP_OPEN|SC_CCP_UP|SC_LOOP_TRAFFIC \
 			 |SC_MULTILINK|SC_MP_SHORTSEQ|SC_MP_XSHORTSEQ \
-			 |SC_COMP_TCP|SC_REJ_COMP_TCP)
+			 |SC_COMP_TCP|SC_REJ_COMP_TCP|SC_MUST_COMP)
 
 /*
  * Private data structure for each channel.
@@ -1027,6 +1028,56 @@ ppp_xmit_process(struct ppp *ppp)
 	ppp_xmit_unlock(ppp);
 }
 
+static inline struct sk_buff *
+pad_compress_skb(struct ppp *ppp, struct sk_buff *skb)
+{
+	struct sk_buff *new_skb;
+	int len;
+	int new_skb_size = ppp->dev->mtu +
+		ppp->xcomp->comp_extra + ppp->dev->hard_header_len;
+	int compressor_skb_size = ppp->dev->mtu +
+		ppp->xcomp->comp_extra + PPP_HDRLEN;
+	new_skb = alloc_skb(new_skb_size, GFP_ATOMIC);
+	if (!new_skb) {
+		if (net_ratelimit())
+			printk(KERN_ERR "PPP: no memory (comp pkt)\n");
+		return NULL;
+	}
+	if (ppp->dev->hard_header_len > PPP_HDRLEN)
+		skb_reserve(new_skb,
+			    ppp->dev->hard_header_len - PPP_HDRLEN);
+
+	/* compressor still expects A/C bytes in hdr */
+	len = ppp->xcomp->compress(ppp->xc_state, skb->data - 2,
+				   new_skb->data, skb->len + 2,
+				   compressor_skb_size);
+	if (len > 0 && (ppp->flags & SC_CCP_UP)) {
+		kfree_skb(skb);
+		skb = new_skb;
+		skb_put(skb, len);
+		skb_pull(skb, 2);	/* pull off A/C bytes */
+	} else if (len == 0) {
+		/* didn't compress, or CCP not up yet */
+		kfree_skb(new_skb);
+		new_skb = skb;
+	} else {
+		/*
+		 * (len < 0)
+		 * MPPE requires that we do not send unencrypted
+		 * frames.  The compressor will return -1 if we
+		 * should drop the frame.  We cannot simply test
+		 * the compress_proto because MPPE and MPPC share
+		 * the same number.
+		 */
+		if (net_ratelimit())
+			printk(KERN_ERR "ppp: compressor dropped pkt\n");
+		kfree_skb(skb);
+		kfree_skb(new_skb);
+		new_skb = NULL;
+	}
+	return new_skb;
+}
+
 /*
  * Compress and send a frame.
  * The caller should have locked the xmit path,
@@ -1113,29 +1164,14 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
 	/* try to do packet compression */
 	if ((ppp->xstate & SC_COMP_RUN) && ppp->xc_state != 0
 	    && proto != PPP_LCP && proto != PPP_CCP) {
-		new_skb = alloc_skb(ppp->dev->mtu + ppp->dev->hard_header_len,
-				    GFP_ATOMIC);
-		if (new_skb == 0) {
-			printk(KERN_ERR "PPP: no memory (comp pkt)\n");
+		if (!(ppp->flags & SC_CCP_UP) && (ppp->flags & SC_MUST_COMP)) {
+			if (net_ratelimit())
+				printk(KERN_ERR "ppp: compression required but down - pkt dropped.\n");
 			goto drop;
 		}
-		if (ppp->dev->hard_header_len > PPP_HDRLEN)
-			skb_reserve(new_skb,
-				    ppp->dev->hard_header_len - PPP_HDRLEN);
-
-		/* compressor still expects A/C bytes in hdr */
-		len = ppp->xcomp->compress(ppp->xc_state, skb->data - 2,
-					   new_skb->data, skb->len + 2,
-					   ppp->dev->mtu + PPP_HDRLEN);
-		if (len > 0 && (ppp->flags & SC_CCP_UP)) {
-			kfree_skb(skb);
-			skb = new_skb;
-			skb_put(skb, len);
-			skb_pull(skb, 2);	/* pull off A/C bytes */
-		} else {
-			/* didn't compress, or CCP not up yet */
-			kfree_skb(new_skb);
-		}
+		skb = pad_compress_skb(ppp, skb);
+		if (!skb)
+			goto drop;
 	}
 
 	/*
@@ -1155,7 +1191,8 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
 	return;
 
  drop:
-	kfree_skb(skb);
+	if (skb)
+		kfree_skb(skb);
 	++ppp->stats.tx_errors;
 }
 
@@ -1552,6 +1589,9 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
 	    && (ppp->rstate & (SC_DC_FERROR | SC_DC_ERROR)) == 0)
 		skb = ppp_decompress_frame(ppp, skb);
 
+	if (ppp->flags & SC_MUST_COMP && ppp->rstate & SC_DC_FERROR)
+		goto err;
+
 	proto = PPP_PROTO(skb);
 	switch (proto) {
 	case PPP_VJC_COMP:
diff --git a/drivers/net/ppp_mppe.c b/drivers/net/ppp_mppe.c
new file mode 100644
index 000000000000..1985d1b57c45
--- /dev/null
+++ b/drivers/net/ppp_mppe.c
@@ -0,0 +1,724 @@
+/*
+ * ppp_mppe.c - interface MPPE to the PPP code.
+ * This version is for use with Linux kernel 2.6.14+
+ *
+ * By Frank Cusack <fcusack@fcusack.com>.
+ * Copyright (c) 2002,2003,2004 Google, Inc.
+ * All rights reserved.
+ *
+ * License:
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation is hereby granted, provided that the above copyright
+ * notice appears in all copies.  This software is provided without any
+ * warranty, express or implied.
+ *
+ * ALTERNATIVELY, provided that this notice is retained in full, this product
+ * may be distributed under the terms of the GNU General Public License (GPL),
+ * in which case the provisions of the GPL apply INSTEAD OF those given above.
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ *
+ * Changelog:
+ *      08/12/05 - Matt Domsch <Matt_Domsch@dell.com>
+ *                 Only need extra skb padding on transmit, not receive.
+ *      06/18/04 - Matt Domsch <Matt_Domsch@dell.com>, Oleg Makarenko <mole@quadra.ru>
+ *                 Use Linux kernel 2.6 arc4 and sha1 routines rather than
+ *                 providing our own.
+ *      2/15/04 - TS: added #include <version.h> and testing for Kernel
+ *                    version before using
+ *                    MOD_DEC_USAGE_COUNT/MOD_INC_USAGE_COUNT which are
+ *                    deprecated in 2.6
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/version.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/crypto.h>
+#include <linux/mm.h>
+#include <linux/ppp_defs.h>
+#include <linux/ppp-comp.h>
+#include <asm/scatterlist.h>
+
+#include "ppp_mppe.h"
+
+MODULE_AUTHOR("Frank Cusack <fcusack@fcusack.com>");
+MODULE_DESCRIPTION("Point-to-Point Protocol Microsoft Point-to-Point Encryption support");
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_ALIAS("ppp-compress-" __stringify(CI_MPPE));
+MODULE_VERSION("1.0.2");
+
+static void
+setup_sg(struct scatterlist *sg, const void *address, unsigned int length)
+{
+	sg[0].page = virt_to_page(address);
+	sg[0].offset = offset_in_page(address);
+	sg[0].length = length;
+}
+
+#define SHA1_PAD_SIZE 40
+
+/*
+ * kernel crypto API needs its arguments to be in kmalloc'd memory, not in the module
+ * static data area.  That means sha_pad needs to be kmalloc'd.
+ */
+
+struct sha_pad {
+	unsigned char sha_pad1[SHA1_PAD_SIZE];
+	unsigned char sha_pad2[SHA1_PAD_SIZE];
+};
+static struct sha_pad *sha_pad;
+
+static inline void sha_pad_init(struct sha_pad *shapad)
+{
+	memset(shapad->sha_pad1, 0x00, sizeof(shapad->sha_pad1));
+	memset(shapad->sha_pad2, 0xF2, sizeof(shapad->sha_pad2));
+}
+
+/*
+ * State for an MPPE (de)compressor.
+ */
+struct ppp_mppe_state {
+	struct crypto_tfm *arc4;
+	struct crypto_tfm *sha1;
+	unsigned char *sha1_digest;
+	unsigned char master_key[MPPE_MAX_KEY_LEN];
+	unsigned char session_key[MPPE_MAX_KEY_LEN];
+	unsigned keylen;	/* key length in bytes             */
+	/* NB: 128-bit == 16, 40-bit == 8! */
+	/* If we want to support 56-bit,   */
+	/* the unit has to change to bits  */
+	unsigned char bits;	/* MPPE control bits */
+	unsigned ccount;	/* 12-bit coherency count (seqno)  */
+	unsigned stateful;	/* stateful mode flag */
+	int discard;		/* stateful mode packet loss flag */
+	int sanity_errors;	/* take down LCP if too many */
+	int unit;
+	int debug;
+	struct compstat stats;
+};
+
+/* struct ppp_mppe_state.bits definitions */
+#define MPPE_BIT_A	0x80	/* Encryption table were (re)inititalized */
+#define MPPE_BIT_B	0x40	/* MPPC only (not implemented) */
+#define MPPE_BIT_C	0x20	/* MPPC only (not implemented) */
+#define MPPE_BIT_D	0x10	/* This is an encrypted frame */
+
+#define MPPE_BIT_FLUSHED	MPPE_BIT_A
+#define MPPE_BIT_ENCRYPTED	MPPE_BIT_D
+
+#define MPPE_BITS(p) ((p)[4] & 0xf0)
+#define MPPE_CCOUNT(p) ((((p)[4] & 0x0f) << 8) + (p)[5])
+#define MPPE_CCOUNT_SPACE 0x1000	/* The size of the ccount space */
+
+#define MPPE_OVHD	2	/* MPPE overhead/packet */
+#define SANITY_MAX	1600	/* Max bogon factor we will tolerate */
+
+/*
+ * 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)
+{
+	struct scatterlist sg[4];
+
+	setup_sg(&sg[0], state->master_key, state->keylen);
+	setup_sg(&sg[1], sha_pad->sha_pad1, sizeof(sha_pad->sha_pad1));
+	setup_sg(&sg[2], state->session_key, state->keylen);
+	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);
+}
+
+/*
+ * Perform the MPPE rekey algorithm, from RFC 3078, sec. 7.3.
+ * Well, not what's written there, but rather what they meant.
+ */
+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);
+	if (!initial_key) {
+		crypto_cipher_setkey(state->arc4, InterimKey, state->keylen);
+		setup_sg(sg_in, InterimKey, 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);
+	}
+	if (state->keylen == 8) {
+		/* See RFC 3078 */
+		state->session_key[0] = 0xd1;
+		state->session_key[1] = 0x26;
+		state->session_key[2] = 0x9e;
+	}
+	crypto_cipher_setkey(state->arc4, state->session_key, state->keylen);
+}
+
+/*
+ * Allocate space for a (de)compressor.
+ */
+static void *mppe_alloc(unsigned char *options, int optlen)
+{
+	struct ppp_mppe_state *state;
+	unsigned int digestsize;
+
+	if (optlen != CILEN_MPPE + sizeof(state->master_key)
+	    || options[0] != CI_MPPE || options[1] != CILEN_MPPE)
+		goto out;
+
+	state = (struct ppp_mppe_state *) kmalloc(sizeof(*state), GFP_KERNEL);
+	if (state == NULL)
+		goto out;
+
+	memset(state, 0, sizeof(*state));
+
+	state->arc4 = crypto_alloc_tfm("arc4", 0);
+	if (!state->arc4)
+		goto out_free;
+
+	state->sha1 = crypto_alloc_tfm("sha1", 0);
+	if (!state->sha1)
+		goto out_free;
+
+	digestsize = crypto_tfm_alg_digestsize(state->sha1);
+	if (digestsize < MPPE_MAX_KEY_LEN)
+		goto out_free;
+
+	state->sha1_digest = kmalloc(digestsize, GFP_KERNEL);
+	if (!state->sha1_digest)
+		goto out_free;
+
+	/* Save keys. */
+	memcpy(state->master_key, &options[CILEN_MPPE],
+	       sizeof(state->master_key));
+	memcpy(state->session_key, state->master_key,
+	       sizeof(state->master_key));
+
+	/*
+	 * We defer initial key generation until mppe_init(), as mppe_alloc()
+	 * is called frequently during negotiation.
+	 */
+
+	return (void *)state;
+
+	out_free:
+	    if (state->sha1_digest)
+		kfree(state->sha1_digest);
+	    if (state->sha1)
+		crypto_free_tfm(state->sha1);
+	    if (state->arc4)
+		crypto_free_tfm(state->arc4);
+	    kfree(state);
+	out:
+	return NULL;
+}
+
+/*
+ * Deallocate space for a (de)compressor.
+ */
+static void mppe_free(void *arg)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+	if (state) {
+	    if (state->sha1_digest)
+		kfree(state->sha1_digest);
+	    if (state->sha1)
+		crypto_free_tfm(state->sha1);
+	    if (state->arc4)
+		crypto_free_tfm(state->arc4);
+	    kfree(state);
+	}
+}
+
+/*
+ * Initialize (de)compressor state.
+ */
+static int
+mppe_init(void *arg, unsigned char *options, int optlen, int unit, int debug,
+	  const char *debugstr)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+	unsigned char mppe_opts;
+
+	if (optlen != CILEN_MPPE
+	    || options[0] != CI_MPPE || options[1] != CILEN_MPPE)
+		return 0;
+
+	MPPE_CI_TO_OPTS(&options[2], mppe_opts);
+	if (mppe_opts & MPPE_OPT_128)
+		state->keylen = 16;
+	else if (mppe_opts & MPPE_OPT_40)
+		state->keylen = 8;
+	else {
+		printk(KERN_WARNING "%s[%d]: unknown key length\n", debugstr,
+		       unit);
+		return 0;
+	}
+	if (mppe_opts & MPPE_OPT_STATEFUL)
+		state->stateful = 1;
+
+	/* Generate the initial session key. */
+	mppe_rekey(state, 1);
+
+	if (debug) {
+		int i;
+		char mkey[sizeof(state->master_key) * 2 + 1];
+		char skey[sizeof(state->session_key) * 2 + 1];
+
+		printk(KERN_DEBUG "%s[%d]: initialized with %d-bit %s mode\n",
+		       debugstr, unit, (state->keylen == 16) ? 128 : 40,
+		       (state->stateful) ? "stateful" : "stateless");
+
+		for (i = 0; i < sizeof(state->master_key); i++)
+			sprintf(mkey + i * 2, "%02x", state->master_key[i]);
+		for (i = 0; i < sizeof(state->session_key); i++)
+			sprintf(skey + i * 2, "%02x", state->session_key[i]);
+		printk(KERN_DEBUG
+		       "%s[%d]: keys: master: %s initial session: %s\n",
+		       debugstr, unit, mkey, skey);
+	}
+
+	/*
+	 * Initialize the coherency count.  The initial value is not specified
+	 * in RFC 3078, but we can make a reasonable assumption that it will
+	 * start at 0.  Setting it to the max here makes the comp/decomp code
+	 * do the right thing (determined through experiment).
+	 */
+	state->ccount = MPPE_CCOUNT_SPACE - 1;
+
+	/*
+	 * Note that even though we have initialized the key table, we don't
+	 * set the FLUSHED bit.  This is contrary to RFC 3078, sec. 3.1.
+	 */
+	state->bits = MPPE_BIT_ENCRYPTED;
+
+	state->unit = unit;
+	state->debug = debug;
+
+	return 1;
+}
+
+static int
+mppe_comp_init(void *arg, unsigned char *options, int optlen, int unit,
+	       int hdrlen, int debug)
+{
+	/* ARGSUSED */
+	return mppe_init(arg, options, optlen, unit, debug, "mppe_comp_init");
+}
+
+/*
+ * We received a CCP Reset-Request (actually, we are sending a Reset-Ack),
+ * tell the compressor to rekey.  Note that we MUST NOT rekey for
+ * every CCP Reset-Request; we only rekey on the next xmit packet.
+ * We might get multiple CCP Reset-Requests if our CCP Reset-Ack is lost.
+ * So, rekeying for every CCP Reset-Request is broken as the peer will not
+ * know how many times we've rekeyed.  (If we rekey and THEN get another
+ * CCP Reset-Request, we must rekey again.)
+ */
+static void mppe_comp_reset(void *arg)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+
+	state->bits |= MPPE_BIT_FLUSHED;
+}
+
+/*
+ * Compress (encrypt) a packet.
+ * It's strange to call this a compressor, since the output is always
+ * MPPE_OVHD + 2 bytes larger than the input.
+ */
+static int
+mppe_compress(void *arg, unsigned char *ibuf, unsigned char *obuf,
+	      int isize, int osize)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+	int proto;
+	struct scatterlist sg_in[1], sg_out[1];
+
+	/*
+	 * Check that the protocol is in the range we handle.
+	 */
+	proto = PPP_PROTOCOL(ibuf);
+	if (proto < 0x0021 || proto > 0x00fa)
+		return 0;
+
+	/* Make sure we have enough room to generate an encrypted packet. */
+	if (osize < isize + MPPE_OVHD + 2) {
+		/* Drop the packet if we should encrypt it, but can't. */
+		printk(KERN_DEBUG "mppe_compress[%d]: osize too small! "
+		       "(have: %d need: %d)\n", state->unit,
+		       osize, osize + MPPE_OVHD + 2);
+		return -1;
+	}
+
+	osize = isize + MPPE_OVHD + 2;
+
+	/*
+	 * Copy over the PPP header and set control bits.
+	 */
+	obuf[0] = PPP_ADDRESS(ibuf);
+	obuf[1] = PPP_CONTROL(ibuf);
+	obuf[2] = PPP_COMP >> 8;	/* isize + MPPE_OVHD + 1 */
+	obuf[3] = PPP_COMP;	/* isize + MPPE_OVHD + 2 */
+	obuf += PPP_HDRLEN;
+
+	state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
+	if (state->debug >= 7)
+		printk(KERN_DEBUG "mppe_compress[%d]: ccount %d\n", state->unit,
+		       state->ccount);
+	obuf[0] = state->ccount >> 8;
+	obuf[1] = state->ccount & 0xff;
+
+	if (!state->stateful ||	/* stateless mode     */
+	    ((state->ccount & 0xff) == 0xff) ||	/* "flag" packet      */
+	    (state->bits & MPPE_BIT_FLUSHED)) {	/* CCP Reset-Request  */
+		/* We must rekey */
+		if (state->debug && state->stateful)
+			printk(KERN_DEBUG "mppe_compress[%d]: rekeying\n",
+			       state->unit);
+		mppe_rekey(state, 0);
+		state->bits |= MPPE_BIT_FLUSHED;
+	}
+	obuf[0] |= state->bits;
+	state->bits &= ~MPPE_BIT_FLUSHED;	/* reset for next xmit */
+
+	obuf += MPPE_OVHD;
+	ibuf += 2;		/* skip to proto field */
+	isize -= 2;
+
+	/* Encrypt packet */
+	setup_sg(sg_in, ibuf, isize);
+	setup_sg(sg_out, obuf, osize);
+	if (crypto_cipher_encrypt(state->arc4, sg_out, sg_in, isize) != 0) {
+		printk(KERN_DEBUG "crypto_cypher_encrypt failed\n");
+		return -1;
+	}
+
+	state->stats.unc_bytes += isize;
+	state->stats.unc_packets++;
+	state->stats.comp_bytes += osize;
+	state->stats.comp_packets++;
+
+	return osize;
+}
+
+/*
+ * Since every frame grows by MPPE_OVHD + 2 bytes, this is always going
+ * to look bad ... and the longer the link is up the worse it will get.
+ */
+static void mppe_comp_stats(void *arg, struct compstat *stats)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+
+	*stats = state->stats;
+}
+
+static int
+mppe_decomp_init(void *arg, unsigned char *options, int optlen, int unit,
+		 int hdrlen, int mru, int debug)
+{
+	/* ARGSUSED */
+	return mppe_init(arg, options, optlen, unit, debug, "mppe_decomp_init");
+}
+
+/*
+ * We received a CCP Reset-Ack.  Just ignore it.
+ */
+static void mppe_decomp_reset(void *arg)
+{
+	/* ARGSUSED */
+	return;
+}
+
+/*
+ * Decompress (decrypt) an MPPE packet.
+ */
+static int
+mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
+		int osize)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+	unsigned ccount;
+	int flushed = MPPE_BITS(ibuf) & MPPE_BIT_FLUSHED;
+	int sanity = 0;
+	struct scatterlist sg_in[1], sg_out[1];
+
+	if (isize <= PPP_HDRLEN + MPPE_OVHD) {
+		if (state->debug)
+			printk(KERN_DEBUG
+			       "mppe_decompress[%d]: short pkt (%d)\n",
+			       state->unit, isize);
+		return DECOMP_ERROR;
+	}
+
+	/*
+	 * Make sure we have enough room to decrypt the packet.
+	 * Note that for our test we only subtract 1 byte whereas in
+	 * mppe_compress() we added 2 bytes (+MPPE_OVHD);
+	 * this is to account for possible PFC.
+	 */
+	if (osize < isize - MPPE_OVHD - 1) {
+		printk(KERN_DEBUG "mppe_decompress[%d]: osize too small! "
+		       "(have: %d need: %d)\n", state->unit,
+		       osize, isize - MPPE_OVHD - 1);
+		return DECOMP_ERROR;
+	}
+	osize = isize - MPPE_OVHD - 2;	/* assume no PFC */
+
+	ccount = MPPE_CCOUNT(ibuf);
+	if (state->debug >= 7)
+		printk(KERN_DEBUG "mppe_decompress[%d]: ccount %d\n",
+		       state->unit, ccount);
+
+	/* sanity checks -- terminate with extreme prejudice */
+	if (!(MPPE_BITS(ibuf) & MPPE_BIT_ENCRYPTED)) {
+		printk(KERN_DEBUG
+		       "mppe_decompress[%d]: ENCRYPTED bit not set!\n",
+		       state->unit);
+		state->sanity_errors += 100;
+		sanity = 1;
+	}
+	if (!state->stateful && !flushed) {
+		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set in "
+		       "stateless mode!\n", state->unit);
+		state->sanity_errors += 100;
+		sanity = 1;
+	}
+	if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
+		printk(KERN_DEBUG "mppe_decompress[%d]: FLUSHED bit not set on "
+		       "flag packet!\n", state->unit);
+		state->sanity_errors += 100;
+		sanity = 1;
+	}
+
+	if (sanity) {
+		if (state->sanity_errors < SANITY_MAX)
+			return DECOMP_ERROR;
+		else
+			/*
+			 * Take LCP down if the peer is sending too many bogons.
+			 * We don't want to do this for a single or just a few
+			 * instances since it could just be due to packet corruption.
+			 */
+			return DECOMP_FATALERROR;
+	}
+
+	/*
+	 * Check the coherency count.
+	 */
+
+	if (!state->stateful) {
+		/* RFC 3078, sec 8.1.  Rekey for every packet. */
+		while (state->ccount != ccount) {
+			mppe_rekey(state, 0);
+			state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
+		}
+	} else {
+		/* RFC 3078, sec 8.2. */
+		if (!state->discard) {
+			/* normal state */
+			state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
+			if (ccount != state->ccount) {
+				/*
+				 * (ccount > state->ccount)
+				 * Packet loss detected, enter the discard state.
+				 * Signal the peer to rekey (by sending a CCP Reset-Request).
+				 */
+				state->discard = 1;
+				return DECOMP_ERROR;
+			}
+		} else {
+			/* discard state */
+			if (!flushed) {
+				/* ccp.c will be silent (no additional CCP Reset-Requests). */
+				return DECOMP_ERROR;
+			} else {
+				/* Rekey for every missed "flag" packet. */
+				while ((ccount & ~0xff) !=
+				       (state->ccount & ~0xff)) {
+					mppe_rekey(state, 0);
+					state->ccount =
+					    (state->ccount +
+					     256) % MPPE_CCOUNT_SPACE;
+				}
+
+				/* reset */
+				state->discard = 0;
+				state->ccount = ccount;
+				/*
+				 * Another problem with RFC 3078 here.  It implies that the
+				 * peer need not send a Reset-Ack packet.  But RFC 1962
+				 * requires it.  Hopefully, M$ does send a Reset-Ack; even
+				 * though it isn't required for MPPE synchronization, it is
+				 * required to reset CCP state.
+				 */
+			}
+		}
+		if (flushed)
+			mppe_rekey(state, 0);
+	}
+
+	/*
+	 * Fill in the first part of the PPP header.  The protocol field
+	 * comes from the decrypted data.
+	 */
+	obuf[0] = PPP_ADDRESS(ibuf);	/* +1 */
+	obuf[1] = PPP_CONTROL(ibuf);	/* +1 */
+	obuf += 2;
+	ibuf += PPP_HDRLEN + MPPE_OVHD;
+	isize -= PPP_HDRLEN + MPPE_OVHD;	/* -6 */
+	/* net osize: isize-4 */
+
+	/*
+	 * Decrypt the first byte in order to check if it is
+	 * a compressed or uncompressed protocol field.
+	 */
+	setup_sg(sg_in, ibuf, 1);
+	setup_sg(sg_out, obuf, 1);
+	if (crypto_cipher_decrypt(state->arc4, sg_out, sg_in, 1) != 0) {
+		printk(KERN_DEBUG "crypto_cypher_decrypt failed\n");
+		return DECOMP_ERROR;
+	}
+
+	/*
+	 * Do PFC decompression.
+	 * This would be nicer if we were given the actual sk_buff
+	 * instead of a char *.
+	 */
+	if ((obuf[0] & 0x01) != 0) {
+		obuf[1] = obuf[0];
+		obuf[0] = 0;
+		obuf++;
+		osize++;
+	}
+
+	/* And finally, decrypt the rest of the packet. */
+	setup_sg(sg_in, ibuf + 1, isize - 1);
+	setup_sg(sg_out, obuf + 1, osize - 1);
+	if (crypto_cipher_decrypt(state->arc4, sg_out, sg_in, isize - 1) != 0) {
+		printk(KERN_DEBUG "crypto_cypher_decrypt failed\n");
+		return DECOMP_ERROR;
+	}
+
+	state->stats.unc_bytes += osize;
+	state->stats.unc_packets++;
+	state->stats.comp_bytes += isize;
+	state->stats.comp_packets++;
+
+	/* good packet credit */
+	state->sanity_errors >>= 1;
+
+	return osize;
+}
+
+/*
+ * Incompressible data has arrived (this should never happen!).
+ * We should probably drop the link if the protocol is in the range
+ * of what should be encrypted.  At the least, we should drop this
+ * packet.  (How to do this?)
+ */
+static void mppe_incomp(void *arg, unsigned char *ibuf, int icnt)
+{
+	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
+
+	if (state->debug &&
+	    (PPP_PROTOCOL(ibuf) >= 0x0021 && PPP_PROTOCOL(ibuf) <= 0x00fa))
+		printk(KERN_DEBUG
+		       "mppe_incomp[%d]: incompressible (unencrypted) data! "
+		       "(proto %04x)\n", state->unit, PPP_PROTOCOL(ibuf));
+
+	state->stats.inc_bytes += icnt;
+	state->stats.inc_packets++;
+	state->stats.unc_bytes += icnt;
+	state->stats.unc_packets++;
+}
+
+/*************************************************************
+ * Module interface table
+ *************************************************************/
+
+/*
+ * Procedures exported to if_ppp.c.
+ */
+static struct compressor ppp_mppe = {
+	.compress_proto = CI_MPPE,
+	.comp_alloc     = mppe_alloc,
+	.comp_free      = mppe_free,
+	.comp_init      = mppe_comp_init,
+	.comp_reset     = mppe_comp_reset,
+	.compress       = mppe_compress,
+	.comp_stat      = mppe_comp_stats,
+	.decomp_alloc   = mppe_alloc,
+	.decomp_free    = mppe_free,
+	.decomp_init    = mppe_decomp_init,
+	.decomp_reset   = mppe_decomp_reset,
+	.decompress     = mppe_decompress,
+	.incomp         = mppe_incomp,
+	.decomp_stat    = mppe_comp_stats,
+	.owner          = THIS_MODULE,
+	.comp_extra     = MPPE_PAD,
+};
+
+/*
+ * ppp_mppe_init()
+ *
+ * Prior to allowing load, try to load the arc4 and sha1 crypto
+ * libraries.  The actual use will be allocated later, but
+ * this way the module will fail to insmod if they aren't available.
+ */
+
+static int __init ppp_mppe_init(void)
+{
+	int answer;
+	if (!(crypto_alg_available("arc4", 0) &&
+	      crypto_alg_available("sha1", 0)))
+		return -ENODEV;
+
+	sha_pad = kmalloc(sizeof(struct sha_pad), GFP_KERNEL);
+	if (!sha_pad)
+		return -ENOMEM;
+	sha_pad_init(sha_pad);
+
+	answer = ppp_register_compressor(&ppp_mppe);
+
+	if (answer == 0)
+		printk(KERN_INFO "PPP MPPE Compression module registered\n");
+	else
+		kfree(sha_pad);
+
+	return answer;
+}
+
+static void __exit ppp_mppe_cleanup(void)
+{
+	ppp_unregister_compressor(&ppp_mppe);
+	kfree(sha_pad);
+}
+
+module_init(ppp_mppe_init);
+module_exit(ppp_mppe_cleanup);
diff --git a/drivers/net/ppp_mppe.h b/drivers/net/ppp_mppe.h
new file mode 100644
index 000000000000..7a14e058c668
--- /dev/null
+++ b/drivers/net/ppp_mppe.h
@@ -0,0 +1,86 @@
+#define MPPE_PAD                4      /* MPPE growth per frame */
+#define MPPE_MAX_KEY_LEN       16      /* largest key length (128-bit) */
+
+/* option bits for ccp_options.mppe */
+#define MPPE_OPT_40            0x01    /* 40 bit */
+#define MPPE_OPT_128           0x02    /* 128 bit */
+#define MPPE_OPT_STATEFUL      0x04    /* stateful mode */
+/* unsupported opts */
+#define MPPE_OPT_56            0x08    /* 56 bit */
+#define MPPE_OPT_MPPC          0x10    /* MPPC compression */
+#define MPPE_OPT_D             0x20    /* Unknown */
+#define MPPE_OPT_UNSUPPORTED (MPPE_OPT_56|MPPE_OPT_MPPC|MPPE_OPT_D)
+#define MPPE_OPT_UNKNOWN       0x40    /* Bits !defined in RFC 3078 were set */
+
+/*
+ * This is not nice ... the alternative is a bitfield struct though.
+ * And unfortunately, we cannot share the same bits for the option
+ * names above since C and H are the same bit.  We could do a u_int32
+ * but then we have to do a htonl() all the time and/or we still need
+ * to know which octet is which.
+ */
+#define MPPE_C_BIT             0x01    /* MPPC */
+#define MPPE_D_BIT             0x10    /* Obsolete, usage unknown */
+#define MPPE_L_BIT             0x20    /* 40-bit */
+#define MPPE_S_BIT             0x40    /* 128-bit */
+#define MPPE_M_BIT             0x80    /* 56-bit, not supported */
+#define MPPE_H_BIT             0x01    /* Stateless (in a different byte) */
+
+/* Does not include H bit; used for least significant octet only. */
+#define MPPE_ALL_BITS (MPPE_D_BIT|MPPE_L_BIT|MPPE_S_BIT|MPPE_M_BIT|MPPE_H_BIT)
+
+/* Build a CI from mppe opts (see RFC 3078) */
+#define MPPE_OPTS_TO_CI(opts, ci)              \
+    do {                                       \
+       u_char *ptr = ci; /* u_char[4] */       \
+                                               \
+       /* H bit */                             \
+       if (opts & MPPE_OPT_STATEFUL)           \
+           *ptr++ = 0x0;                       \
+       else                                    \
+           *ptr++ = MPPE_H_BIT;                \
+       *ptr++ = 0;                             \
+       *ptr++ = 0;                             \
+                                               \
+       /* S,L bits */                          \
+       *ptr = 0;                               \
+       if (opts & MPPE_OPT_128)                \
+           *ptr |= MPPE_S_BIT;                 \
+       if (opts & MPPE_OPT_40)                 \
+           *ptr |= MPPE_L_BIT;                 \
+       /* M,D,C bits not supported */          \
+    } while (/* CONSTCOND */ 0)
+
+/* The reverse of the above */
+#define MPPE_CI_TO_OPTS(ci, opts)              \
+    do {                                       \
+       u_char *ptr = ci; /* u_char[4] */       \
+                                               \
+       opts = 0;                               \
+                                               \
+       /* H bit */                             \
+       if (!(ptr[0] & MPPE_H_BIT))             \
+           opts |= MPPE_OPT_STATEFUL;          \
+                                               \
+       /* S,L bits */                          \
+       if (ptr[3] & MPPE_S_BIT)                \
+           opts |= MPPE_OPT_128;               \
+       if (ptr[3] & MPPE_L_BIT)                \
+           opts |= MPPE_OPT_40;                \
+                                               \
+       /* M,D,C bits */                        \
+       if (ptr[3] & MPPE_M_BIT)                \
+           opts |= MPPE_OPT_56;                \
+       if (ptr[3] & MPPE_D_BIT)                \
+           opts |= MPPE_OPT_D;                 \
+       if (ptr[3] & MPPE_C_BIT)                \
+           opts |= MPPE_OPT_MPPC;              \
+                                               \
+       /* Other bits */                        \
+       if (ptr[0] & ~MPPE_H_BIT)               \
+           opts |= MPPE_OPT_UNKNOWN;           \
+       if (ptr[1] || ptr[2])                   \
+           opts |= MPPE_OPT_UNKNOWN;           \
+       if (ptr[3] & ~MPPE_ALL_BITS)            \
+           opts |= MPPE_OPT_UNKNOWN;           \
+    } while (/* CONSTCOND */ 0)