--- /dev/null
+/* Module signature checker
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/err.h>
+#include <crypto/public_key.h>
+#include <crypto/hash.h>
+#include <keys/asymmetric-type.h>
+#include <keys/system_keyring.h>
+#include "module-internal.h"
+
+/*
+ * Module signature information block.
+ *
+ * The constituents of the signature section are, in order:
+ *
+ * - Signer's name
+ * - Key identifier
+ * - Signature data
+ * - Information block
+ */
+struct module_signature {
+ u8 algo; /* Public-key crypto algorithm [enum pkey_algo] */
+ u8 hash; /* Digest algorithm [enum hash_algo] */
+ u8 id_type; /* Key identifier type [enum pkey_id_type] */
+ u8 signer_len; /* Length of signer's name */
+ u8 key_id_len; /* Length of key identifier */
+ u8 __pad[3];
+ __be32 sig_len; /* Length of signature data */
+};
+
+/*
+ * Digest the module contents.
+ */
+static struct public_key_signature *mod_make_digest(enum hash_algo hash,
+ const void *mod,
+ unsigned long modlen)
+{
+ struct public_key_signature *pks;
+ struct crypto_shash *tfm;
+ struct shash_desc *desc;
+ size_t digest_size, desc_size;
+ int ret;
+
+ pr_devel("==>%s()\n", __func__);
+
+ /* Allocate the hashing algorithm we're going to need and find out how
+ * big the hash operational data will be.
+ */
+ tfm = crypto_alloc_shash(hash_algo_name[hash], 0, 0);
+ if (IS_ERR(tfm))
+ return (PTR_ERR(tfm) == -ENOENT) ? ERR_PTR(-ENOPKG) : ERR_CAST(tfm);
+
+ desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+ digest_size = crypto_shash_digestsize(tfm);
+
+ /* We allocate the hash operational data storage on the end of our
+ * context data and the digest output buffer on the end of that.
+ */
+ ret = -ENOMEM;
+ pks = kzalloc(digest_size + sizeof(*pks) + desc_size, GFP_KERNEL);
+ if (!pks)
+ goto error_no_pks;
+
+ pks->pkey_hash_algo = hash;
+ pks->digest = (u8 *)pks + sizeof(*pks) + desc_size;
+ pks->digest_size = digest_size;
+
+ desc = (void *)pks + sizeof(*pks);
+ desc->tfm = tfm;
+ desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+
+ ret = crypto_shash_init(desc);
+ if (ret < 0)
+ goto error;
+
+ ret = crypto_shash_finup(desc, mod, modlen, pks->digest);
+ if (ret < 0)
+ goto error;
+
+ crypto_free_shash(tfm);
+ pr_devel("<==%s() = ok\n", __func__);
+ return pks;
+
+error:
+ kfree(pks);
+error_no_pks:
+ crypto_free_shash(tfm);
+ pr_devel("<==%s() = %d\n", __func__, ret);
+ return ERR_PTR(ret);
+}
+
+/*
+ * Extract an MPI array from the signature data. This represents the actual
+ * signature. Each raw MPI is prefaced by a BE 2-byte value indicating the
+ * size of the MPI in bytes.
+ *
+ * RSA signatures only have one MPI, so currently we only read one.
+ */
+static int mod_extract_mpi_array(struct public_key_signature *pks,
+ const void *data, size_t len)
+{
+ size_t nbytes;
+ MPI mpi;
+
+ if (len < 3)
+ return -EBADMSG;
+ nbytes = ((const u8 *)data)[0] << 8 | ((const u8 *)data)[1];
+ data += 2;
+ len -= 2;
+ if (len != nbytes)
+ return -EBADMSG;
+
+ mpi = mpi_read_raw_data(data, nbytes);
+ if (!mpi)
+ return -ENOMEM;
+ pks->mpi[0] = mpi;
+ pks->nr_mpi = 1;
+ return 0;
+}
+
+/*
+ * Request an asymmetric key.
+ */
+static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
+ const u8 *key_id, size_t key_id_len)
+{
+ key_ref_t key;
+ size_t i;
+ char *id, *q;
+
+ pr_devel("==>%s(,%zu,,%zu)\n", __func__, signer_len, key_id_len);
+
+ /* Construct an identifier. */
+ id = kmalloc(signer_len + 2 + key_id_len * 2 + 1, GFP_KERNEL);
+ if (!id)
+ return ERR_PTR(-ENOKEY);
+
+ memcpy(id, signer, signer_len);
+
+ q = id + signer_len;
+ *q++ = ':';
+ *q++ = ' ';
+ for (i = 0; i < key_id_len; i++) {
+ *q++ = hex_asc[*key_id >> 4];
+ *q++ = hex_asc[*key_id++ & 0x0f];
+ }
+
+ *q = 0;
+
+ pr_debug("Look up: \"%s\"\n", id);
+
+ key = keyring_search(make_key_ref(system_trusted_keyring, 1),
+ &key_type_asymmetric, id);
+ if (IS_ERR(key))
+ pr_warn("Request for unknown module key '%s' err %ld\n",
+ id, PTR_ERR(key));
+ kfree(id);
+
+ if (IS_ERR(key)) {
+ switch (PTR_ERR(key)) {
+ /* Hide some search errors */
+ case -EACCES:
+ case -ENOTDIR:
+ case -EAGAIN:
+ return ERR_PTR(-ENOKEY);
+ default:
+ return ERR_CAST(key);
+ }
+ }
+
+ pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
+ return key_ref_to_ptr(key);
+}
+
+/*
+ * Verify the signature on a module.
+ */
+int mod_verify_sig(const void *mod, unsigned long *_modlen)
+{
+ struct public_key_signature *pks;
+ struct module_signature ms;
+ struct key *key;
+ const void *sig;
+ size_t modlen = *_modlen, sig_len;
+ int ret;
+
+ pr_devel("==>%s(,%zu)\n", __func__, modlen);
+
+ if (modlen <= sizeof(ms))
+ return -EBADMSG;
+
+ memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
+ modlen -= sizeof(ms);
+
+ sig_len = be32_to_cpu(ms.sig_len);
+ if (sig_len >= modlen)
+ return -EBADMSG;
+ modlen -= sig_len;
+ if ((size_t)ms.signer_len + ms.key_id_len >= modlen)
+ return -EBADMSG;
+ modlen -= (size_t)ms.signer_len + ms.key_id_len;
+
+ *_modlen = modlen;
+ sig = mod + modlen;
+
+ /* For the moment, only support RSA and X.509 identifiers */
+ if (ms.algo != PKEY_ALGO_RSA ||
+ ms.id_type != PKEY_ID_X509)
+ return -ENOPKG;
+
+ if (ms.hash >= PKEY_HASH__LAST ||
+ !hash_algo_name[ms.hash])
+ return -ENOPKG;
+
+ key = request_asymmetric_key(sig, ms.signer_len,
+ sig + ms.signer_len, ms.key_id_len);
+ if (IS_ERR(key))
+ return PTR_ERR(key);
+
+ pks = mod_make_digest(ms.hash, mod, modlen);
+ if (IS_ERR(pks)) {
+ ret = PTR_ERR(pks);
+ goto error_put_key;
+ }
+
+ ret = mod_extract_mpi_array(pks, sig + ms.signer_len + ms.key_id_len,
+ sig_len);
+ if (ret < 0)
+ goto error_free_pks;
+
+ ret = verify_signature(key, pks);
+ pr_devel("verify_signature() = %d\n", ret);
+
+error_free_pks:
+ mpi_free(pks->rsa.s);
+ kfree(pks);
+error_put_key:
+ key_put(key);
+ pr_devel("<==%s() = %d\n", __func__, ret);
+ return ret;
+}
Code Review / kvmfornfv.git / blobdiff