/* * 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/err.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 unsigned int 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; return 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_blkcipher *arc4; struct crypto_hash *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 hash_desc desc; struct scatterlist sg[4]; unsigned int nbytes; nbytes = setup_sg(&sg[0], state->master_key, state->keylen); nbytes += setup_sg(&sg[1], sha_pad->sha_pad1, sizeof(sha_pad->sha_pad1)); nbytes += setup_sg(&sg[2], state->session_key, state->keylen); nbytes += setup_sg(&sg[3], sha_pad->sha_pad2, sizeof(sha_pad->sha_pad2)); desc.tfm = state->sha1; desc.flags = 0; crypto_hash_digest(&desc, sg, nbytes, 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]; struct blkcipher_desc desc = { .tfm = state->arc4 }; get_new_key_from_sha(state, InterimKey); if (!initial_key) { crypto_blkcipher_setkey(state->arc4, InterimKey, state->keylen); setup_sg(sg_in, InterimKey, 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); } if (state->keylen == 8) { /* See RFC 3078 */ state->session_key[0] = 0xd1; state->session_key[1] = 0x26; state->session_key[2] = 0x9e; } crypto_blkcipher_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 = kmalloc(sizeof(*state), GFP_KERNEL); if (state == NULL) goto out; memset(state, 0, sizeof(*state)); state->arc4 = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); if (IS_ERR(state->arc4)) { state->arc4 = NULL; goto out_free; } state->sha1 = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC); if (IS_ERR(state->sha1)) { state->sha1 = NULL; goto out_free; } digestsize = crypto_hash_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_hash(state->sha1); if (state->arc4) crypto_free_blkcipher(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_hash(state->sha1); if (state->arc4) crypto_free_blkcipher(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; struct blkcipher_desc desc = { .tfm = state->arc4 }; 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_blkcipher_encrypt(&desc, 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; struct blkcipher_desc desc = { .tfm = state->arc4 }; 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_blkcipher_decrypt(&desc, 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_blkcipher_decrypt(&desc, sg_out, sg_in, isize - 1)) { 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_has_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC) && crypto_has_hash("sha1", 0, CRYPTO_ALG_ASYNC))) 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);