diff options
Diffstat (limited to 'crypto/asymmetric_keys/pkcs7_verify.c')
| -rw-r--r-- | crypto/asymmetric_keys/pkcs7_verify.c | 361 |
1 files changed, 361 insertions, 0 deletions
diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c new file mode 100644 index 000000000..cd455450b --- /dev/null +++ b/crypto/asymmetric_keys/pkcs7_verify.c @@ -0,0 +1,361 @@ +/* Verify the signature on a PKCS#7 message. + * + * 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. + */ + +#define pr_fmt(fmt) "PKCS7: "fmt +#include <linux/kernel.h> +#include <linux/export.h> +#include <linux/slab.h> +#include <linux/err.h> +#include <linux/asn1.h> +#include <crypto/hash.h> +#include "public_key.h" +#include "pkcs7_parser.h" + +/* + * Digest the relevant parts of the PKCS#7 data + */ +static int pkcs7_digest(struct pkcs7_message *pkcs7, + struct pkcs7_signed_info *sinfo) +{ + struct crypto_shash *tfm; + struct shash_desc *desc; + size_t digest_size, desc_size; + void *digest; + int ret; + + kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo); + + if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST || + !hash_algo_name[sinfo->sig.pkey_hash_algo]) + return -ENOPKG; + + /* 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[sinfo->sig.pkey_hash_algo], + 0, 0); + if (IS_ERR(tfm)) + return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm); + + desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); + sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm); + + ret = -ENOMEM; + digest = kzalloc(digest_size + desc_size, GFP_KERNEL); + if (!digest) + goto error_no_desc; + + desc = digest + digest_size; + desc->tfm = tfm; + desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; + + /* Digest the message [RFC2315 9.3] */ + ret = crypto_shash_init(desc); + if (ret < 0) + goto error; + ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest); + if (ret < 0) + goto error; + pr_devel("MsgDigest = [%*ph]\n", 8, digest); + + /* However, if there are authenticated attributes, there must be a + * message digest attribute amongst them which corresponds to the + * digest we just calculated. + */ + if (sinfo->msgdigest) { + u8 tag; + + if (sinfo->msgdigest_len != sinfo->sig.digest_size) { + pr_debug("Sig %u: Invalid digest size (%u)\n", + sinfo->index, sinfo->msgdigest_len); + ret = -EBADMSG; + goto error; + } + + if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) { + pr_debug("Sig %u: Message digest doesn't match\n", + sinfo->index); + ret = -EKEYREJECTED; + goto error; + } + + /* We then calculate anew, using the authenticated attributes + * as the contents of the digest instead. Note that we need to + * convert the attributes from a CONT.0 into a SET before we + * hash it. + */ + memset(digest, 0, sinfo->sig.digest_size); + + ret = crypto_shash_init(desc); + if (ret < 0) + goto error; + tag = ASN1_CONS_BIT | ASN1_SET; + ret = crypto_shash_update(desc, &tag, 1); + if (ret < 0) + goto error; + ret = crypto_shash_finup(desc, sinfo->authattrs, + sinfo->authattrs_len, digest); + if (ret < 0) + goto error; + pr_devel("AADigest = [%*ph]\n", 8, digest); + } + + sinfo->sig.digest = digest; + digest = NULL; + +error: + kfree(digest); +error_no_desc: + crypto_free_shash(tfm); + kleave(" = %d", ret); + return ret; +} + +/* + * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7 + * uses the issuer's name and the issuing certificate serial number for + * matching purposes. These must match the certificate issuer's name (not + * subject's name) and the certificate serial number [RFC 2315 6.7]. + */ +static int pkcs7_find_key(struct pkcs7_message *pkcs7, + struct pkcs7_signed_info *sinfo) +{ + struct x509_certificate *x509; + unsigned certix = 1; + + kenter("%u", sinfo->index); + + for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) { + /* I'm _assuming_ that the generator of the PKCS#7 message will + * encode the fields from the X.509 cert in the same way in the + * PKCS#7 message - but I can't be 100% sure of that. It's + * possible this will need element-by-element comparison. + */ + if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id)) + continue; + pr_devel("Sig %u: Found cert serial match X.509[%u]\n", + sinfo->index, certix); + + if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) { + pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n", + sinfo->index); + continue; + } + + sinfo->signer = x509; + return 0; + } + + /* The relevant X.509 cert isn't found here, but it might be found in + * the trust keyring. + */ + pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n", + sinfo->index, + sinfo->signing_cert_id->len, sinfo->signing_cert_id->data); + return 0; +} + +/* + * Verify the internal certificate chain as best we can. + */ +static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7, + struct pkcs7_signed_info *sinfo) +{ + struct x509_certificate *x509 = sinfo->signer, *p; + int ret; + + kenter(""); + + for (p = pkcs7->certs; p; p = p->next) + p->seen = false; + + for (;;) { + pr_debug("verify %s: %*phN\n", + x509->subject, + x509->raw_serial_size, x509->raw_serial); + x509->seen = true; + ret = x509_get_sig_params(x509); + if (ret < 0) + goto maybe_missing_crypto_in_x509; + + pr_debug("- issuer %s\n", x509->issuer); + if (x509->authority) + pr_debug("- authkeyid %*phN\n", + x509->authority->len, x509->authority->data); + + if (!x509->authority || + strcmp(x509->subject, x509->issuer) == 0) { + /* If there's no authority certificate specified, then + * the certificate must be self-signed and is the root + * of the chain. Likewise if the cert is its own + * authority. + */ + pr_debug("- no auth?\n"); + if (x509->raw_subject_size != x509->raw_issuer_size || + memcmp(x509->raw_subject, x509->raw_issuer, + x509->raw_issuer_size) != 0) + return 0; + + ret = x509_check_signature(x509->pub, x509); + if (ret < 0) + goto maybe_missing_crypto_in_x509; + x509->signer = x509; + pr_debug("- self-signed\n"); + return 0; + } + + /* Look through the X.509 certificates in the PKCS#7 message's + * list to see if the next one is there. + */ + pr_debug("- want %*phN\n", + x509->authority->len, x509->authority->data); + for (p = pkcs7->certs; p; p = p->next) { + if (!p->skid) + continue; + pr_debug("- cmp [%u] %*phN\n", + p->index, p->skid->len, p->skid->data); + if (asymmetric_key_id_same(p->skid, x509->authority)) + goto found_issuer; + } + + /* We didn't find the root of this chain */ + pr_debug("- top\n"); + return 0; + + found_issuer: + pr_debug("- subject %s\n", p->subject); + if (p->seen) { + pr_warn("Sig %u: X.509 chain contains loop\n", + sinfo->index); + return 0; + } + ret = x509_check_signature(p->pub, x509); + if (ret < 0) + return ret; + x509->signer = p; + if (x509 == p) { + pr_debug("- self-signed\n"); + return 0; + } + x509 = p; + might_sleep(); + } + +maybe_missing_crypto_in_x509: + /* Just prune the certificate chain at this point if we lack some + * crypto module to go further. Note, however, we don't want to set + * sinfo->missing_crypto as the signed info block may still be + * validatable against an X.509 cert lower in the chain that we have a + * trusted copy of. + */ + if (ret == -ENOPKG) + return 0; + return ret; +} + +/* + * Verify one signed information block from a PKCS#7 message. + */ +static int pkcs7_verify_one(struct pkcs7_message *pkcs7, + struct pkcs7_signed_info *sinfo) +{ + int ret; + + kenter(",%u", sinfo->index); + + /* First of all, digest the data in the PKCS#7 message and the + * signed information block + */ + ret = pkcs7_digest(pkcs7, sinfo); + if (ret < 0) + return ret; + + /* Find the key for the signature if there is one */ + ret = pkcs7_find_key(pkcs7, sinfo); + if (ret < 0) + return ret; + + if (!sinfo->signer) + return 0; + + pr_devel("Using X.509[%u] for sig %u\n", + sinfo->signer->index, sinfo->index); + + /* Verify the PKCS#7 binary against the key */ + ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig); + if (ret < 0) + return ret; + + pr_devel("Verified signature %u\n", sinfo->index); + + /* Verify the internal certificate chain */ + return pkcs7_verify_sig_chain(pkcs7, sinfo); +} + +/** + * pkcs7_verify - Verify a PKCS#7 message + * @pkcs7: The PKCS#7 message to be verified + * + * Verify a PKCS#7 message is internally consistent - that is, the data digest + * matches the digest in the AuthAttrs and any signature in the message or one + * of the X.509 certificates it carries that matches another X.509 cert in the + * message can be verified. + * + * This does not look to match the contents of the PKCS#7 message against any + * external public keys. + * + * Returns, in order of descending priority: + * + * (*) -EKEYREJECTED if a signature failed to match for which we found an + * appropriate X.509 certificate, or: + * + * (*) -EBADMSG if some part of the message was invalid, or: + * + * (*) -ENOPKG if none of the signature chains are verifiable because suitable + * crypto modules couldn't be found, or: + * + * (*) 0 if all the signature chains that don't incur -ENOPKG can be verified + * (note that a signature chain may be of zero length), or: + */ +int pkcs7_verify(struct pkcs7_message *pkcs7) +{ + struct pkcs7_signed_info *sinfo; + struct x509_certificate *x509; + int enopkg = -ENOPKG; + int ret, n; + + kenter(""); + + for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) { + ret = x509_get_sig_params(x509); + if (ret < 0) + return ret; + pr_debug("X.509[%u] %*phN\n", + n, x509->authority->len, x509->authority->data); + } + + for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) { + ret = pkcs7_verify_one(pkcs7, sinfo); + if (ret < 0) { + if (ret == -ENOPKG) { + sinfo->unsupported_crypto = true; + continue; + } + kleave(" = %d", ret); + return ret; + } + enopkg = 0; + } + + kleave(" = %d", enopkg); + return enopkg; +} +EXPORT_SYMBOL_GPL(pkcs7_verify); |