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lib/digsig.c
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// SPDX-License-Identifier: GPL-2.0-only |
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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> * |
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* 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; |
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static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg, unsigned long msglen, unsigned long modulus_bitlen, unsigned long *outlen) |
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{ unsigned long modulus_len, ps_len, i; |
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modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); /* test message size */ if ((msglen > modulus_len) || (modulus_len < 11)) |
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return NULL; |
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/* separate encoded message */ |
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if (msg[0] != 0x00 || msg[1] != 0x01) return NULL; |
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for (i = 2; i < modulus_len - 1; i++) if (msg[i] != 0xFF) break; /* separator check */ |
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if (msg[i] != 0) |
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/* There was no octet with hexadecimal value 0x00 to separate ps from m. */ |
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return NULL; |
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ps_len = i - 2; |
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*outlen = (msglen - (2 + ps_len + 1)); |
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return msg + 2 + ps_len + 1; |
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} /* * 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; |
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int head, i; |
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unsigned char *out1 = NULL; const char *m; |
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MPI in = NULL, res = NULL, pkey[2]; |
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uint8_t *p, *datap; const uint8_t *endp; const struct user_key_payload *ukp; |
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struct pubkey_hdr *pkh; down_read(&key->sem); |
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ukp = user_key_payload_locked(key); |
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if (!ukp) { /* key was revoked before we acquired its semaphore */ err = -EKEYREVOKED; goto err1; } |
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if (ukp->datalen < sizeof(*pkh)) goto err1; |
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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; |
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endp = ukp->data + ukp->datalen; |
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for (i = 0; i < pkh->nmpi; i++) { unsigned int remaining = endp - datap; pkey[i] = mpi_read_from_buffer(datap, &remaining); |
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if (IS_ERR(pkey[i])) { err = PTR_ERR(pkey[i]); |
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goto err; |
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} |
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datap += remaining; } mblen = mpi_get_nbits(pkey[0]); |
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mlen = DIV_ROUND_UP(mblen, 8); |
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if (mlen == 0) { err = -EINVAL; |
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goto err; |
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} err = -ENOMEM; |
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out1 = kzalloc(mlen, GFP_KERNEL); if (!out1) goto err; |
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nret = siglen; in = mpi_read_from_buffer(sig, &nret); |
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if (IS_ERR(in)) { err = PTR_ERR(in); |
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goto err; |
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} |
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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); |
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kfree(p); |
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m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len); |
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if (!m || len != hlen || memcmp(m, h, hlen)) |
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err = -EINVAL; |
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err: mpi_free(in); mpi_free(res); kfree(out1); |
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while (--i >= 0) mpi_free(pkey[i]); |
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err1: up_read(&key->sem); return err; } /** * digsig_verify() - digital signature verification with public key * @keyring: keyring to search key in * @sig: digital signature |
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* @siglen: length of the signature |
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* @data: data * @datalen: length of the data |
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* * Returns 0 on success, -EINVAL otherwise |
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* * 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), |
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&key_type_user, name, true); |
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if (IS_ERR(kref)) |
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key = ERR_CAST(kref); |
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else key = key_ref_to_ptr(kref); } else { |
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key = request_key(&key_type_user, name, NULL, NULL); |
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} if (IS_ERR(key)) { pr_err("key not found, id: %s ", name); return PTR_ERR(key); } desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash), GFP_KERNEL); if (!desc) goto err; desc->tfm = shash; |
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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 "); 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"); |