linux/security/keys/dh.c

363 lines
7.6 KiB
C

/* Crypto operations using stored keys
*
* Copyright (c) 2016, Intel Corporation
*
* 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.
*/
#include <linux/mpi.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/crypto.h>
#include <crypto/hash.h>
#include <keys/user-type.h>
#include "internal.h"
/*
* Public key or shared secret generation function [RFC2631 sec 2.1.1]
*
* ya = g^xa mod p;
* or
* ZZ = yb^xa mod p;
*
* where xa is the local private key, ya is the local public key, g is
* the generator, p is the prime, yb is the remote public key, and ZZ
* is the shared secret.
*
* Both are the same calculation, so g or yb are the "base" and ya or
* ZZ are the "result".
*/
static int do_dh(MPI result, MPI base, MPI xa, MPI p)
{
return mpi_powm(result, base, xa, p);
}
static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
{
struct key *key;
key_ref_t key_ref;
long status;
ssize_t ret;
key_ref = lookup_user_key(keyid, 0, KEY_NEED_READ);
if (IS_ERR(key_ref)) {
ret = -ENOKEY;
goto error;
}
key = key_ref_to_ptr(key_ref);
ret = -EOPNOTSUPP;
if (key->type == &key_type_user) {
down_read(&key->sem);
status = key_validate(key);
if (status == 0) {
const struct user_key_payload *payload;
payload = user_key_payload_locked(key);
if (maxlen == 0) {
*mpi = NULL;
ret = payload->datalen;
} else if (payload->datalen <= maxlen) {
*mpi = mpi_read_raw_data(payload->data,
payload->datalen);
if (*mpi)
ret = payload->datalen;
} else {
ret = -EINVAL;
}
}
up_read(&key->sem);
}
key_put(key);
error:
return ret;
}
struct kdf_sdesc {
struct shash_desc shash;
char ctx[];
};
static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
{
struct crypto_shash *tfm;
struct kdf_sdesc *sdesc;
int size;
/* allocate synchronous hash */
tfm = crypto_alloc_shash(hashname, 0, 0);
if (IS_ERR(tfm)) {
pr_info("could not allocate digest TFM handle %s\n", hashname);
return PTR_ERR(tfm);
}
size = sizeof(struct shash_desc) + crypto_shash_descsize(tfm);
sdesc = kmalloc(size, GFP_KERNEL);
if (!sdesc)
return -ENOMEM;
sdesc->shash.tfm = tfm;
sdesc->shash.flags = 0x0;
*sdesc_ret = sdesc;
return 0;
}
static void kdf_dealloc(struct kdf_sdesc *sdesc)
{
if (!sdesc)
return;
if (sdesc->shash.tfm)
crypto_free_shash(sdesc->shash.tfm);
kzfree(sdesc);
}
/* convert 32 bit integer into its string representation */
static inline void crypto_kw_cpu_to_be32(u32 val, u8 *buf)
{
__be32 *a = (__be32 *)buf;
*a = cpu_to_be32(val);
}
/*
* Implementation of the KDF in counter mode according to SP800-108 section 5.1
* as well as SP800-56A section 5.8.1 (Single-step KDF).
*
* SP800-56A:
* The src pointer is defined as Z || other info where Z is the shared secret
* from DH and other info is an arbitrary string (see SP800-56A section
* 5.8.1.2).
*/
static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
u8 *dst, unsigned int dlen)
{
struct shash_desc *desc = &sdesc->shash;
unsigned int h = crypto_shash_digestsize(desc->tfm);
int err = 0;
u8 *dst_orig = dst;
u32 i = 1;
u8 iteration[sizeof(u32)];
while (dlen) {
err = crypto_shash_init(desc);
if (err)
goto err;
crypto_kw_cpu_to_be32(i, iteration);
err = crypto_shash_update(desc, iteration, sizeof(u32));
if (err)
goto err;
if (src && slen) {
err = crypto_shash_update(desc, src, slen);
if (err)
goto err;
}
if (dlen < h) {
u8 tmpbuffer[h];
err = crypto_shash_final(desc, tmpbuffer);
if (err)
goto err;
memcpy(dst, tmpbuffer, dlen);
memzero_explicit(tmpbuffer, h);
return 0;
} else {
err = crypto_shash_final(desc, dst);
if (err)
goto err;
dlen -= h;
dst += h;
i++;
}
}
return 0;
err:
memzero_explicit(dst_orig, dlen);
return err;
}
static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
char __user *buffer, size_t buflen,
uint8_t *kbuf, size_t kbuflen)
{
uint8_t *outbuf = NULL;
int ret;
outbuf = kmalloc(buflen, GFP_KERNEL);
if (!outbuf) {
ret = -ENOMEM;
goto err;
}
ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, buflen);
if (ret)
goto err;
ret = buflen;
if (copy_to_user(buffer, outbuf, buflen) != 0)
ret = -EFAULT;
err:
kzfree(outbuf);
return ret;
}
long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
char __user *buffer, size_t buflen,
struct keyctl_kdf_params *kdfcopy)
{
long ret;
MPI base, private, prime, result;
unsigned nbytes;
struct keyctl_dh_params pcopy;
uint8_t *kbuf;
ssize_t keylen;
size_t resultlen;
struct kdf_sdesc *sdesc = NULL;
if (!params || (!buffer && buflen)) {
ret = -EINVAL;
goto out;
}
if (copy_from_user(&pcopy, params, sizeof(pcopy)) != 0) {
ret = -EFAULT;
goto out;
}
if (kdfcopy) {
char *hashname;
if (buflen > KEYCTL_KDF_MAX_OUTPUT_LEN ||
kdfcopy->otherinfolen > KEYCTL_KDF_MAX_OI_LEN) {
ret = -EMSGSIZE;
goto out;
}
/* get KDF name string */
hashname = strndup_user(kdfcopy->hashname, CRYPTO_MAX_ALG_NAME);
if (IS_ERR(hashname)) {
ret = PTR_ERR(hashname);
goto out;
}
/* allocate KDF from the kernel crypto API */
ret = kdf_alloc(&sdesc, hashname);
kfree(hashname);
if (ret)
goto out;
}
/*
* If the caller requests postprocessing with a KDF, allow an
* arbitrary output buffer size since the KDF ensures proper truncation.
*/
keylen = mpi_from_key(pcopy.prime, kdfcopy ? SIZE_MAX : buflen, &prime);
if (keylen < 0 || !prime) {
/* buflen == 0 may be used to query the required buffer size,
* which is the prime key length.
*/
ret = keylen;
goto out;
}
/* The result is never longer than the prime */
resultlen = keylen;
keylen = mpi_from_key(pcopy.base, SIZE_MAX, &base);
if (keylen < 0 || !base) {
ret = keylen;
goto error1;
}
keylen = mpi_from_key(pcopy.private, SIZE_MAX, &private);
if (keylen < 0 || !private) {
ret = keylen;
goto error2;
}
result = mpi_alloc(0);
if (!result) {
ret = -ENOMEM;
goto error3;
}
/* allocate space for DH shared secret and SP800-56A otherinfo */
kbuf = kmalloc(kdfcopy ? (resultlen + kdfcopy->otherinfolen) : resultlen,
GFP_KERNEL);
if (!kbuf) {
ret = -ENOMEM;
goto error4;
}
/*
* Concatenate SP800-56A otherinfo past DH shared secret -- the
* input to the KDF is (DH shared secret || otherinfo)
*/
if (kdfcopy && kdfcopy->otherinfo &&
copy_from_user(kbuf + resultlen, kdfcopy->otherinfo,
kdfcopy->otherinfolen) != 0) {
ret = -EFAULT;
goto error5;
}
ret = do_dh(result, base, private, prime);
if (ret)
goto error5;
ret = mpi_read_buffer(result, kbuf, resultlen, &nbytes, NULL);
if (ret != 0)
goto error5;
if (kdfcopy) {
ret = keyctl_dh_compute_kdf(sdesc, buffer, buflen, kbuf,
resultlen + kdfcopy->otherinfolen);
} else {
ret = nbytes;
if (copy_to_user(buffer, kbuf, nbytes) != 0)
ret = -EFAULT;
}
error5:
kzfree(kbuf);
error4:
mpi_free(result);
error3:
mpi_free(private);
error2:
mpi_free(base);
error1:
mpi_free(prime);
out:
kdf_dealloc(sdesc);
return ret;
}
long keyctl_dh_compute(struct keyctl_dh_params __user *params,
char __user *buffer, size_t buflen,
struct keyctl_kdf_params __user *kdf)
{
struct keyctl_kdf_params kdfcopy;
if (!kdf)
return __keyctl_dh_compute(params, buffer, buflen, NULL);
if (copy_from_user(&kdfcopy, kdf, sizeof(kdfcopy)) != 0)
return -EFAULT;
return __keyctl_dh_compute(params, buffer, buflen, &kdfcopy);
}