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Diffstat (limited to '')
| -rw-r--r-- | lib/digsig.c | 279 |
1 files changed, 279 insertions, 0 deletions
diff --git a/lib/digsig.c b/lib/digsig.c new file mode 100644 index 000000000..04b5e55ed --- /dev/null +++ b/lib/digsig.c @@ -0,0 +1,279 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2011 Nokia Corporation + * Copyright (C) 2011 Intel Corporation + * + * Author: + * Dmitry Kasatkin <dmitry.kasatkin@nokia.com> + * <dmitry.kasatkin@intel.com> + * + * 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/sha1.h> +#include <keys/user-type.h> +#include <linux/mpi.h> +#include <linux/digsig.h> + +static struct crypto_shash *shash; + +static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg, + unsigned long msglen, + unsigned long modulus_bitlen, + 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 NULL; + + /* separate encoded message */ + if (msg[0] != 0x00 || msg[1] != 0x01) + return NULL; + + 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 NULL; + + ps_len = i - 2; + + *outlen = (msglen - (2 + ps_len + 1)); + + return msg + 2 + ps_len + 1; +} + +/* + * 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; + const char *m; + MPI in = NULL, res = NULL, pkey[2]; + uint8_t *p, *datap; + const uint8_t *endp; + const struct user_key_payload *ukp; + struct pubkey_hdr *pkh; + + down_read(&key->sem); + ukp = user_key_payload_locked(key); + + if (!ukp) { + /* key was revoked before we acquired its semaphore */ + err = -EKEYREVOKED; + goto err1; + } + + if (ukp-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; + + for (i = 0; i < pkh->nmpi; i++) { + unsigned int remaining = endp - datap; + pkey[i] = mpi_read_from_buffer(datap, &remaining); + if (IS_ERR(pkey[i])) { + err = PTR_ERR(pkey[i]); + goto err; + } + datap += remaining; + } + + mblen = mpi_get_nbits(pkey[0]); + mlen = DIV_ROUND_UP(mblen, 8); + + if (mlen == 0) { + err = -EINVAL; + goto err; + } + + err = -ENOMEM; + + out1 = kzalloc(mlen, GFP_KERNEL); + if (!out1) + goto err; + + nret = siglen; + in = mpi_read_from_buffer(sig, &nret); + if (IS_ERR(in)) { + err = PTR_ERR(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); + + kfree(p); + + m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len); + + if (!m || len != hlen || memcmp(m, h, hlen)) + err = -EINVAL; + +err: + mpi_free(in); + mpi_free(res); + kfree(out1); + 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 + * @siglen: length of the signature + * @data: data + * @datalen: length of the data + * + * Returns 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, true); + if (IS_ERR(kref)) + key = ERR_CAST(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; + + 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"); |