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ppp: mppe: switch to RC4 library interface
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The MPPE code uses the sync skcipher to invoke the ecb(arc4) skcipher,
of which only a single generic C code implementation exists. This means
that going through all the trouble of using scatterlists etc buys us
very little, and we're better off just invoking the arc4 library directly.

Note that the SHA1 shash used by this driver has several accelerated
implementations for various architectures, so retaining that part does
make sense.

Cc: linux-ppp@vger.kernel.org
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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Ard Biesheuvel authored and Herbert Xu committed Jun 20, 2019
1 parent 611a23c commit 0e5a610
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Showing 2 changed files with 15 additions and 85 deletions.
3 changes: 1 addition & 2 deletions drivers/net/ppp/Kconfig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -86,8 +86,7 @@ config PPP_MPPE
depends on PPP
select CRYPTO
select CRYPTO_SHA1
select CRYPTO_ARC4
select CRYPTO_ECB
select CRYPTO_LIB_ARC4
---help---
Support for the MPPE Encryption protocol, as employed by the
Microsoft Point-to-Point Tunneling Protocol.
Expand Down
97 changes: 14 additions & 83 deletions drivers/net/ppp/ppp_mppe.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,9 +42,10 @@
* deprecated in 2.6
*/

#include <crypto/arc4.h>
#include <crypto/hash.h>
#include <crypto/skcipher.h>
#include <linux/err.h>
#include <linux/fips.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
Expand All @@ -65,13 +66,6 @@ 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_set_buf(sg, address, length);
return length;
}

#define SHA1_PAD_SIZE 40

/*
Expand All @@ -95,7 +89,7 @@ static inline void sha_pad_init(struct sha_pad *shapad)
* State for an MPPE (de)compressor.
*/
struct ppp_mppe_state {
struct crypto_sync_skcipher *arc4;
struct arc4_ctx arc4;
struct shash_desc *sha1;
unsigned char *sha1_digest;
unsigned char master_key[MPPE_MAX_KEY_LEN];
Expand Down Expand Up @@ -154,24 +148,11 @@ static void get_new_key_from_sha(struct ppp_mppe_state * state)
*/
static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
{
struct scatterlist sg_in[1], sg_out[1];
SYNC_SKCIPHER_REQUEST_ON_STACK(req, state->arc4);

skcipher_request_set_sync_tfm(req, state->arc4);
skcipher_request_set_callback(req, 0, NULL, NULL);

get_new_key_from_sha(state);
if (!initial_key) {
crypto_sync_skcipher_setkey(state->arc4, state->sha1_digest,
state->keylen);
sg_init_table(sg_in, 1);
sg_init_table(sg_out, 1);
setup_sg(sg_in, state->sha1_digest, state->keylen);
setup_sg(sg_out, state->session_key, state->keylen);
skcipher_request_set_crypt(req, sg_in, sg_out, state->keylen,
NULL);
if (crypto_skcipher_encrypt(req))
printk(KERN_WARNING "mppe_rekey: cipher_encrypt failed\n");
arc4_setkey(&state->arc4, state->sha1_digest, state->keylen);
arc4_crypt(&state->arc4, state->session_key, state->sha1_digest,
state->keylen);
} else {
memcpy(state->session_key, state->sha1_digest, state->keylen);
}
Expand All @@ -181,9 +162,7 @@ static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
state->session_key[1] = 0x26;
state->session_key[2] = 0x9e;
}
crypto_sync_skcipher_setkey(state->arc4, state->session_key,
state->keylen);
skcipher_request_zero(req);
arc4_setkey(&state->arc4, state->session_key, state->keylen);
}

/*
Expand All @@ -196,20 +175,15 @@ static void *mppe_alloc(unsigned char *options, int optlen)
unsigned int digestsize;

if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
options[0] != CI_MPPE || options[1] != CILEN_MPPE)
options[0] != CI_MPPE || options[1] != CILEN_MPPE ||
fips_enabled)
goto out;

state = kzalloc(sizeof(*state), GFP_KERNEL);
if (state == NULL)
goto out;


state->arc4 = crypto_alloc_sync_skcipher("ecb(arc4)", 0, 0);
if (IS_ERR(state->arc4)) {
state->arc4 = NULL;
goto out_free;
}

shash = crypto_alloc_shash("sha1", 0, 0);
if (IS_ERR(shash))
goto out_free;
Expand Down Expand Up @@ -250,7 +224,6 @@ static void *mppe_alloc(unsigned char *options, int optlen)
crypto_free_shash(state->sha1->tfm);
kzfree(state->sha1);
}
crypto_free_sync_skcipher(state->arc4);
kfree(state);
out:
return NULL;
Expand All @@ -266,8 +239,7 @@ static void mppe_free(void *arg)
kfree(state->sha1_digest);
crypto_free_shash(state->sha1->tfm);
kzfree(state->sha1);
crypto_free_sync_skcipher(state->arc4);
kfree(state);
kzfree(state);
}
}

Expand Down Expand Up @@ -366,10 +338,7 @@ mppe_compress(void *arg, unsigned char *ibuf, unsigned char *obuf,
int isize, int osize)
{
struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
SYNC_SKCIPHER_REQUEST_ON_STACK(req, state->arc4);
int proto;
int err;
struct scatterlist sg_in[1], sg_out[1];

/*
* Check that the protocol is in the range we handle.
Expand Down Expand Up @@ -420,21 +389,7 @@ mppe_compress(void *arg, unsigned char *ibuf, unsigned char *obuf,
ibuf += 2; /* skip to proto field */
isize -= 2;

/* Encrypt packet */
sg_init_table(sg_in, 1);
sg_init_table(sg_out, 1);
setup_sg(sg_in, ibuf, isize);
setup_sg(sg_out, obuf, osize);

skcipher_request_set_sync_tfm(req, state->arc4);
skcipher_request_set_callback(req, 0, NULL, NULL);
skcipher_request_set_crypt(req, sg_in, sg_out, isize, NULL);
err = crypto_skcipher_encrypt(req);
skcipher_request_zero(req);
if (err) {
printk(KERN_DEBUG "crypto_cypher_encrypt failed\n");
return -1;
}
arc4_crypt(&state->arc4, obuf, ibuf, isize);

state->stats.unc_bytes += isize;
state->stats.unc_packets++;
Expand Down Expand Up @@ -480,10 +435,8 @@ mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
int osize)
{
struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
SYNC_SKCIPHER_REQUEST_ON_STACK(req, state->arc4);
unsigned ccount;
int flushed = MPPE_BITS(ibuf) & MPPE_BIT_FLUSHED;
struct scatterlist sg_in[1], sg_out[1];

if (isize <= PPP_HDRLEN + MPPE_OVHD) {
if (state->debug)
Expand Down Expand Up @@ -610,19 +563,7 @@ mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
* Decrypt the first byte in order to check if it is
* a compressed or uncompressed protocol field.
*/
sg_init_table(sg_in, 1);
sg_init_table(sg_out, 1);
setup_sg(sg_in, ibuf, 1);
setup_sg(sg_out, obuf, 1);

skcipher_request_set_sync_tfm(req, state->arc4);
skcipher_request_set_callback(req, 0, NULL, NULL);
skcipher_request_set_crypt(req, sg_in, sg_out, 1, NULL);
if (crypto_skcipher_decrypt(req)) {
printk(KERN_DEBUG "crypto_cypher_decrypt failed\n");
osize = DECOMP_ERROR;
goto out_zap_req;
}
arc4_crypt(&state->arc4, obuf, ibuf, 1);

/*
* Do PFC decompression.
Expand All @@ -637,14 +578,7 @@ mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
}

/* And finally, decrypt the rest of the packet. */
setup_sg(sg_in, ibuf + 1, isize - 1);
setup_sg(sg_out, obuf + 1, osize - 1);
skcipher_request_set_crypt(req, sg_in, sg_out, isize - 1, NULL);
if (crypto_skcipher_decrypt(req)) {
printk(KERN_DEBUG "crypto_cypher_decrypt failed\n");
osize = DECOMP_ERROR;
goto out_zap_req;
}
arc4_crypt(&state->arc4, obuf + 1, ibuf + 1, isize - 1);

state->stats.unc_bytes += osize;
state->stats.unc_packets++;
Expand All @@ -654,8 +588,6 @@ mppe_decompress(void *arg, unsigned char *ibuf, int isize, unsigned char *obuf,
/* good packet credit */
state->sanity_errors >>= 1;

out_zap_req:
skcipher_request_zero(req);
return osize;

sanity_error:
Expand Down Expand Up @@ -728,8 +660,7 @@ static struct compressor ppp_mppe = {
static int __init ppp_mppe_init(void)
{
int answer;
if (!(crypto_has_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC) &&
crypto_has_ahash("sha1", 0, CRYPTO_ALG_ASYNC)))
if (fips_enabled || !crypto_has_ahash("sha1", 0, CRYPTO_ALG_ASYNC))
return -ENODEV;

sha_pad = kmalloc(sizeof(struct sha_pad), GFP_KERNEL);
Expand Down

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