cregit-Linux how code gets into the kernel

Release 4.10 crypto/asymmetric_keys/pkcs7_verify.c

/* Verify the signature on a PKCS#7 message.
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (
 * 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; }


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/* * 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; }


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/* * 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("- %*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; }


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/* * 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); }


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/** * 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; }


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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; }


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