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/*
* Copyright (C) 2011 Nokia Corporation
* Copyright (C) 2011 Intel Corporation
*
* Author:
* Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
* <dmitry.kasatkin@intel.com>
*
* 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, version 2 of the License.
*
* File: sign.c
* implements signature (RSA) verification
* pkcs decoding is based on LibTomCrypt code
*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/err.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/key.h>
#include <linux/crypto.h>
#include <crypto/hash.h>
#include <crypto/sha.h>
#include <keys/user-type.h>
#include <linux/mpi.h>
#include <linux/digsig.h>

static struct crypto_shash *shash;

static int pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
unsigned long msglen,
unsigned long modulus_bitlen,
unsigned char *out,
unsigned long *outlen)
{
unsigned long modulus_len, ps_len, i;

modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);

/* test message size */
if ((msglen > modulus_len) || (modulus_len < 11))
return -EINVAL;

/* separate encoded message */
if ((msg[0] != 0x00) || (msg[1] != (unsigned char)1))
return -EINVAL;

for (i = 2; i < modulus_len - 1; i++)
if (msg[i] != 0xFF)
break;

/* separator check */
if (msg[i] != 0)
/* There was no octet with hexadecimal value 0x00
to separate ps from m. */
return -EINVAL;

ps_len = i - 2;

if (*outlen < (msglen - (2 + ps_len + 1))) {
*outlen = msglen - (2 + ps_len + 1);
return -EOVERFLOW;
}

*outlen = (msglen - (2 + ps_len + 1));
memcpy(out, &msg[2 + ps_len + 1], *outlen);

return 0;
}

/*
* RSA Signature verification with public key
*/
static int digsig_verify_rsa(struct key *key,
const char *sig, int siglen,
const char *h, int hlen)
{
int err = -EINVAL;
unsigned long len;
unsigned long mlen, mblen;
unsigned nret, l;
int head, i;
unsigned char *out1 = NULL, *out2 = NULL;
MPI in = NULL, res = NULL, pkey[2];
uint8_t *p, *datap, *endp;
struct user_key_payload *ukp;
struct pubkey_hdr *pkh;

down_read(&key->sem);
ukp = key->payload.data;

if (ukp->datalen < sizeof(*pkh))
goto err1;

pkh = (struct pubkey_hdr *)ukp->data;

if (pkh->version != 1)
goto err1;

if (pkh->algo != PUBKEY_ALGO_RSA)
goto err1;

if (pkh->nmpi != 2)
goto err1;

datap = pkh->mpi;
endp = ukp->data + ukp->datalen;

err = -ENOMEM;

for (i = 0; i < pkh->nmpi; i++) {
unsigned int remaining = endp - datap;
pkey[i] = mpi_read_from_buffer(datap, &remaining);
if (!pkey[i])
goto err;
datap += remaining;
}

mblen = mpi_get_nbits(pkey[0]);
mlen = (mblen + 7)/8;

if (mlen == 0)
goto err;

out1 = kzalloc(mlen, GFP_KERNEL);
if (!out1)
goto err;

out2 = kzalloc(mlen, GFP_KERNEL);
if (!out2)
goto err;

nret = siglen;
in = mpi_read_from_buffer(sig, &nret);
if (!in)
goto err;

res = mpi_alloc(mpi_get_nlimbs(in) * 2);
if (!res)
goto err;

err = mpi_powm(res, in, pkey[1], pkey[0]);
if (err)
goto err;

if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
err = -EINVAL;
goto err;
}

p = mpi_get_buffer(res, &l, NULL);
if (!p) {
err = -EINVAL;
goto err;
}

len = mlen;
head = len - l;
memset(out1, 0, head);
memcpy(out1 + head, p, l);

err = pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len);
if (err)
goto err;

if (len != hlen || memcmp(out2, h, hlen))
err = -EINVAL;

err:
mpi_free(in);
mpi_free(res);
kfree(out1);
kfree(out2);
while (--i >= 0)
mpi_free(pkey[i]);
err1:
up_read(&key->sem);

return err;
}

/**
* digsig_verify() - digital signature verification with public key
* @keyring: keyring to search key in
* @sig: digital signature
* @sigen: length of the signature
* @data: data
* @datalen: length of the data
* @return: 0 on success, -EINVAL otherwise
*
* Verifies data integrity against digital signature.
* Currently only RSA is supported.
* Normally hash of the content is used as a data for this function.
*
*/
int digsig_verify(struct key *keyring, const char *sig, int siglen,
const char *data, int datalen)
{
int err = -ENOMEM;
struct signature_hdr *sh = (struct signature_hdr *)sig;
struct shash_desc *desc = NULL;
unsigned char hash[SHA1_DIGEST_SIZE];
struct key *key;
char name[20];

if (siglen < sizeof(*sh) + 2)
return -EINVAL;

if (sh->algo != PUBKEY_ALGO_RSA)
return -ENOTSUPP;

sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));

if (keyring) {
/* search in specific keyring */
key_ref_t kref;
kref = keyring_search(make_key_ref(keyring, 1UL),
&key_type_user, name);
if (IS_ERR(kref))
key = ERR_PTR(PTR_ERR(kref));
else
key = key_ref_to_ptr(kref);
} else {
key = request_key(&key_type_user, name, NULL);
}
if (IS_ERR(key)) {
pr_err("key not found, id: %s\n", name);
return PTR_ERR(key);
}

desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
GFP_KERNEL);
if (!desc)
goto err;

desc->tfm = shash;
desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

crypto_shash_init(desc);
crypto_shash_update(desc, data, datalen);
crypto_shash_update(desc, sig, sizeof(*sh));
crypto_shash_final(desc, hash);

kfree(desc);

/* pass signature mpis address */
err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
hash, sizeof(hash));

err:
key_put(key);

return err ? -EINVAL : 0;
}
EXPORT_SYMBOL_GPL(digsig_verify);

static int __init digsig_init(void)
{
shash = crypto_alloc_shash("sha1", 0, 0);
if (IS_ERR(shash)) {
pr_err("shash allocation failed\n");
return PTR_ERR(shash);
}

return 0;

}

static void __exit digsig_cleanup(void)
{
crypto_free_shash(shash);
}

module_init(digsig_init);
module_exit(digsig_cleanup);

MODULE_LICENSE("GPL");
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