/* 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 <crypto/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 public_key_signature *sig = sinfo->sig;
        struct crypto_shash *tfm;
        struct shash_desc *desc;
        size_t desc_size;
        int ret;

        kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);

        if (!sinfo->sig->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(sinfo->sig->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);
        sig->digest_size = crypto_shash_digestsize(tfm);

        ret = -ENOMEM;
        sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
        if (!sig->digest)
                goto error_no_desc;

        desc = kzalloc(desc_size, GFP_KERNEL);
        if (!desc)
                goto error_no_desc;

        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,
                                 sig->digest);
        if (ret < 0)
                goto error;
        pr_devel("MsgDigest = [%*ph]\n", 8, sig->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->authattrs) {
                u8 tag;

                if (!sinfo->msgdigest) {
                        pr_warn("Sig %u: No messageDigest\n", sinfo->index);
                        ret = -EKEYREJECTED;
                        goto error;
                }

                if (sinfo->msgdigest_len != sig->digest_size) {
                        pr_debug("Sig %u: Invalid digest size (%u)\n",
                                 sinfo->index, sinfo->msgdigest_len);
                        ret = -EBADMSG;
                        goto error;
                }

                if (memcmp(sig->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(sig->digest, 0, 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, sig->digest);
                if (ret < 0)
                        goto error;
                pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
        }

error:
        kfree(desc);
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->sig->auth_ids[0]))
                        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->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->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 public_key_signature *sig;
        struct x509_certificate *x509 = sinfo->signer, *p;
        struct asymmetric_key_id *auth;
        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;
                if (x509->unsupported_key)
                        goto unsupported_crypto_in_x509;

                pr_debug("- issuer %s\n", x509->issuer);
                sig = x509->sig;
                if (sig->auth_ids[0])
                        pr_debug("- authkeyid.id %*phN\n",
                                 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
                if (sig->auth_ids[1])
                        pr_debug("- authkeyid.skid %*phN\n",
                                 sig->auth_ids[1]->len, sig->auth_ids[1]->data);

                if (x509->self_signed) {
                        /* 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.
                         */
                        if (x509->unsupported_sig)
                                goto unsupported_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.
                 */
                auth = sig->auth_ids[0];
                if (auth) {
                        pr_debug("- want %*phN\n", auth->len, auth->data);
                        for (p = pkcs7->certs; p; p = p->next) {
                                pr_debug("- cmp [%u] %*phN\n",
                                         p->index, p->id->len, p->id->data);
                                if (asymmetric_key_id_same(p->id, auth))
                                        goto found_issuer_check_skid;
                        }
                } else if (sig->auth_ids[1]) {
                        auth = sig->auth_ids[1];
                        pr_debug("- want %*phN\n", auth->len, auth->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, auth))
                                        goto found_issuer;
                        }
                }

                /* We didn't find the root of this chain */
                pr_debug("- top\n");
                return 0;

        found_issuer_check_skid:
                /* We matched issuer + serialNumber, but if there's an
                 * authKeyId.keyId, that must match the CA subjKeyId also.
                 */
                if (sig->auth_ids[1] &&
                    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
                        pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
                                sinfo->index, x509->index, p->index);
                        return -EKEYREJECTED;
                }
        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 = public_key_verify_signature(p->pub, p->sig);
                if (ret < 0)
                        return ret;
                x509->signer = p;
                if (x509 == p) {
                        pr_debug("- self-signed\n");
                        return 0;
                }
                x509 = p;
                might_sleep();
        }

unsupported_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->unsupported_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.
         */
        return 0;
}

/*
 * 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);

        /* Check that the PKCS#7 signing time is valid according to the X.509
         * certificate.  We can't, however, check against the system clock
         * since that may not have been set yet and may be wrong.
         */
        if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
                if (sinfo->signing_time < sinfo->signer->valid_from ||
                    sinfo->signing_time > sinfo->signer->valid_to) {
                        pr_warn("Message signed outside of X.509 validity window\n");
                        return -EKEYREJECTED;
                }
        }

        /* 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
 * @usage: The use to which the key is being put
 *
 * 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 key was selected that had a usage restriction at
 *      odds with the specified usage, or:
 *
 *  (*) -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,
                 enum key_being_used_for usage)
{
        struct pkcs7_signed_info *sinfo;
        int enopkg = -ENOPKG;
        int ret;

        kenter("");

        switch (usage) {
        case VERIFYING_MODULE_SIGNATURE:
                if (pkcs7->data_type != OID_data) {
                        pr_warn("Invalid module sig (not pkcs7-data)\n");
                        return -EKEYREJECTED;
                }
                if (pkcs7->have_authattrs) {
                        pr_warn("Invalid module sig (has authattrs)\n");
                        return -EKEYREJECTED;
                }
                break;
        case VERIFYING_FIRMWARE_SIGNATURE:
                if (pkcs7->data_type != OID_data) {
                        pr_warn("Invalid firmware sig (not pkcs7-data)\n");
                        return -EKEYREJECTED;
                }
                if (!pkcs7->have_authattrs) {
                        pr_warn("Invalid firmware sig (missing authattrs)\n");
                        return -EKEYREJECTED;
                }
                break;
        case VERIFYING_KEXEC_PE_SIGNATURE:
                if (pkcs7->data_type != OID_msIndirectData) {
                        pr_warn("Invalid kexec sig (not Authenticode)\n");
                        return -EKEYREJECTED;
                }
                /* Authattr presence checked in parser */
                break;
        case VERIFYING_UNSPECIFIED_SIGNATURE:
                if (pkcs7->data_type != OID_data) {
                        pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
                        return -EKEYREJECTED;
                }
                break;
        default:
                return -EINVAL;
        }

        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);

/**
 * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 * @pkcs7: The PKCS#7 message
 * @data: The data to be verified
 * @datalen: The amount of data
 *
 * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 * attempt to retain/pin the data is made.  That is left to the caller.  The
 * data will not be modified by pkcs7_verify() and will not be freed when the
 * PKCS#7 message is freed.
 *
 * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 */
int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
                               const void *data, size_t datalen)
{
        if (pkcs7->data) {
                pr_debug("Data already supplied\n");
                return -EINVAL;
        }
        pkcs7->data = data;
        pkcs7->data_len = datalen;
        return 0;
}