--- /dev/null
+/* 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);
Code Review / kvmfornfv.git / blobdiff