2014-07-01 15:02:51 +00:00
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/* Parse a signed PE binary
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*
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* Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#define pr_fmt(fmt) "PEFILE: "fmt
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/err.h>
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#include <linux/pe.h>
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2014-07-01 15:02:51 +00:00
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#include <linux/asn1.h>
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2014-07-01 15:02:51 +00:00
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#include <crypto/pkcs7.h>
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#include <crypto/hash.h>
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#include "verify_pefile.h"
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/*
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* Parse a PE binary.
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*/
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static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
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struct pefile_context *ctx)
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{
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const struct mz_hdr *mz = pebuf;
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const struct pe_hdr *pe;
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const struct pe32_opt_hdr *pe32;
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const struct pe32plus_opt_hdr *pe64;
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const struct data_directory *ddir;
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const struct data_dirent *dde;
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const struct section_header *secs, *sec;
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size_t cursor, datalen = pelen;
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kenter("");
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#define chkaddr(base, x, s) \
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do { \
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if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
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return -ELIBBAD; \
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} while (0)
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chkaddr(0, 0, sizeof(*mz));
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if (mz->magic != MZ_MAGIC)
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return -ELIBBAD;
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cursor = sizeof(*mz);
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chkaddr(cursor, mz->peaddr, sizeof(*pe));
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pe = pebuf + mz->peaddr;
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if (pe->magic != PE_MAGIC)
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return -ELIBBAD;
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cursor = mz->peaddr + sizeof(*pe);
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chkaddr(0, cursor, sizeof(pe32->magic));
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pe32 = pebuf + cursor;
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pe64 = pebuf + cursor;
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switch (pe32->magic) {
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case PE_OPT_MAGIC_PE32:
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chkaddr(0, cursor, sizeof(*pe32));
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ctx->image_checksum_offset =
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(unsigned long)&pe32->csum - (unsigned long)pebuf;
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ctx->header_size = pe32->header_size;
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cursor += sizeof(*pe32);
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ctx->n_data_dirents = pe32->data_dirs;
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break;
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case PE_OPT_MAGIC_PE32PLUS:
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chkaddr(0, cursor, sizeof(*pe64));
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ctx->image_checksum_offset =
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(unsigned long)&pe64->csum - (unsigned long)pebuf;
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ctx->header_size = pe64->header_size;
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cursor += sizeof(*pe64);
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ctx->n_data_dirents = pe64->data_dirs;
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break;
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default:
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pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic);
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return -ELIBBAD;
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}
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pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
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pr_debug("header size = %x\n", ctx->header_size);
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if (cursor >= ctx->header_size || ctx->header_size >= datalen)
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return -ELIBBAD;
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if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
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return -ELIBBAD;
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ddir = pebuf + cursor;
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cursor += sizeof(*dde) * ctx->n_data_dirents;
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ctx->cert_dirent_offset =
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(unsigned long)&ddir->certs - (unsigned long)pebuf;
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ctx->certs_size = ddir->certs.size;
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if (!ddir->certs.virtual_address || !ddir->certs.size) {
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pr_debug("Unsigned PE binary\n");
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return -EKEYREJECTED;
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}
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chkaddr(ctx->header_size, ddir->certs.virtual_address,
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ddir->certs.size);
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ctx->sig_offset = ddir->certs.virtual_address;
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ctx->sig_len = ddir->certs.size;
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pr_debug("cert = %x @%x [%*ph]\n",
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ctx->sig_len, ctx->sig_offset,
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ctx->sig_len, pebuf + ctx->sig_offset);
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ctx->n_sections = pe->sections;
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if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
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return -ELIBBAD;
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ctx->secs = secs = pebuf + cursor;
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return 0;
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}
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2014-07-01 15:02:51 +00:00
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/*
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* Check and strip the PE wrapper from around the signature and check that the
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* remnant looks something like PKCS#7.
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*/
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static int pefile_strip_sig_wrapper(const void *pebuf,
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struct pefile_context *ctx)
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{
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struct win_certificate wrapper;
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const u8 *pkcs7;
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if (ctx->sig_len < sizeof(wrapper)) {
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pr_debug("Signature wrapper too short\n");
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return -ELIBBAD;
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}
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memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
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pr_debug("sig wrapper = { %x, %x, %x }\n",
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wrapper.length, wrapper.revision, wrapper.cert_type);
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/* Both pesign and sbsign round up the length of certificate table
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* (in optional header data directories) to 8 byte alignment.
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*/
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if (round_up(wrapper.length, 8) != ctx->sig_len) {
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pr_debug("Signature wrapper len wrong\n");
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return -ELIBBAD;
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}
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if (wrapper.revision != WIN_CERT_REVISION_2_0) {
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pr_debug("Signature is not revision 2.0\n");
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return -ENOTSUPP;
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}
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if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
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pr_debug("Signature certificate type is not PKCS\n");
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return -ENOTSUPP;
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}
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/* Looks like actual pkcs signature length is in wrapper->length.
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* size obtained from data dir entries lists the total size of
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* certificate table which is also aligned to octawrod boundary.
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*
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* So set signature length field appropriately.
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*/
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ctx->sig_len = wrapper.length;
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ctx->sig_offset += sizeof(wrapper);
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ctx->sig_len -= sizeof(wrapper);
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if (ctx->sig_len == 0) {
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pr_debug("Signature data missing\n");
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return -EKEYREJECTED;
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}
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/* What's left should a PKCS#7 cert */
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pkcs7 = pebuf + ctx->sig_offset;
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if (pkcs7[0] == (ASN1_CONS_BIT | ASN1_SEQ)) {
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if (pkcs7[1] == 0x82 &&
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pkcs7[2] == (((ctx->sig_len - 4) >> 8) & 0xff) &&
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pkcs7[3] == ((ctx->sig_len - 4) & 0xff))
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return 0;
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if (pkcs7[1] == 0x80)
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return 0;
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if (pkcs7[1] > 0x82)
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return -EMSGSIZE;
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}
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pr_debug("Signature data not PKCS#7\n");
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return -ELIBBAD;
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}
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2014-07-01 15:02:51 +00:00
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/**
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* verify_pefile_signature - Verify the signature on a PE binary image
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* @pebuf: Buffer containing the PE binary image
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* @pelen: Length of the binary image
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* @trust_keyring: Signing certificates to use as starting points
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* @_trusted: Set to true if trustworth, false otherwise
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*
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* Validate that the certificate chain inside the PKCS#7 message inside the PE
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* binary image intersects keys we already know and trust.
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*
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* Returns, in order of descending priority:
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*
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* (*) -ELIBBAD if the image cannot be parsed, or:
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*
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* (*) -EKEYREJECTED if a signature failed to match for which we have a valid
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* key, or:
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*
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* (*) 0 if at least one signature chain intersects with the keys in the trust
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* keyring, or:
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*
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* (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
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* chain.
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*
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* (*) -ENOKEY if we couldn't find a match for any of the signature chains in
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* the message.
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*
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* May also return -ENOMEM.
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*/
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int verify_pefile_signature(const void *pebuf, unsigned pelen,
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struct key *trusted_keyring, bool *_trusted)
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{
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struct pefile_context ctx;
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int ret;
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kenter("");
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memset(&ctx, 0, sizeof(ctx));
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ret = pefile_parse_binary(pebuf, pelen, &ctx);
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if (ret < 0)
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return ret;
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2014-07-01 15:02:51 +00:00
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ret = pefile_strip_sig_wrapper(pebuf, &ctx);
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if (ret < 0)
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return ret;
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2014-07-01 15:02:51 +00:00
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return -ENOANO; // Not yet complete
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}
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