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452 lines
11 KiB
452 lines
11 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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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 ([email protected]) |
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*/ |
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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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#include <linux/asn1.h> |
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#include <linux/verification.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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/* |
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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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|
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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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|
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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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|
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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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|
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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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|
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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 -ENODATA; |
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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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/* |
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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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unsigned len; |
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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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/* It looks like the pkcs signature length in wrapper->length and the |
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* size obtained from the data dir entries, which lists the total size |
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* of certificate table, are both aligned to an octaword boundary, so |
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* we may have to deal with some padding. |
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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 < 4) { |
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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 be 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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goto not_pkcs7; |
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switch (pkcs7[1]) { |
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case 0 ... 0x7f: |
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len = pkcs7[1] + 2; |
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goto check_len; |
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case ASN1_INDEFINITE_LENGTH: |
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return 0; |
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case 0x81: |
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len = pkcs7[2] + 3; |
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goto check_len; |
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case 0x82: |
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len = ((pkcs7[2] << 8) | pkcs7[3]) + 4; |
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goto check_len; |
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case 0x83 ... 0xff: |
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return -EMSGSIZE; |
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default: |
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goto not_pkcs7; |
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} |
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check_len: |
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if (len <= ctx->sig_len) { |
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/* There may be padding */ |
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ctx->sig_len = len; |
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return 0; |
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} |
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not_pkcs7: |
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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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/* |
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* Compare two sections for canonicalisation. |
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*/ |
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static int pefile_compare_shdrs(const void *a, const void *b) |
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{ |
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const struct section_header *shdra = a; |
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const struct section_header *shdrb = b; |
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int rc; |
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if (shdra->data_addr > shdrb->data_addr) |
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return 1; |
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if (shdrb->data_addr > shdra->data_addr) |
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return -1; |
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if (shdra->virtual_address > shdrb->virtual_address) |
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return 1; |
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if (shdrb->virtual_address > shdra->virtual_address) |
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return -1; |
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rc = strcmp(shdra->name, shdrb->name); |
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if (rc != 0) |
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return rc; |
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if (shdra->virtual_size > shdrb->virtual_size) |
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return 1; |
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if (shdrb->virtual_size > shdra->virtual_size) |
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return -1; |
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if (shdra->raw_data_size > shdrb->raw_data_size) |
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return 1; |
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if (shdrb->raw_data_size > shdra->raw_data_size) |
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return -1; |
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return 0; |
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} |
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/* |
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* Load the contents of the PE binary into the digest, leaving out the image |
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* checksum and the certificate data block. |
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*/ |
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static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen, |
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struct pefile_context *ctx, |
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struct shash_desc *desc) |
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{ |
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unsigned *canon, tmp, loop, i, hashed_bytes; |
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int ret; |
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/* Digest the header and data directory, but leave out the image |
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* checksum and the data dirent for the signature. |
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*/ |
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ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset); |
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if (ret < 0) |
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return ret; |
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tmp = ctx->image_checksum_offset + sizeof(uint32_t); |
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ret = crypto_shash_update(desc, pebuf + tmp, |
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ctx->cert_dirent_offset - tmp); |
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if (ret < 0) |
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return ret; |
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tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent); |
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ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp); |
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if (ret < 0) |
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return ret; |
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canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL); |
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if (!canon) |
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return -ENOMEM; |
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/* We have to canonicalise the section table, so we perform an |
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* insertion sort. |
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*/ |
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canon[0] = 0; |
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for (loop = 1; loop < ctx->n_sections; loop++) { |
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for (i = 0; i < loop; i++) { |
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if (pefile_compare_shdrs(&ctx->secs[canon[i]], |
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&ctx->secs[loop]) > 0) { |
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memmove(&canon[i + 1], &canon[i], |
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(loop - i) * sizeof(canon[0])); |
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break; |
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} |
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} |
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canon[i] = loop; |
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} |
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hashed_bytes = ctx->header_size; |
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for (loop = 0; loop < ctx->n_sections; loop++) { |
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i = canon[loop]; |
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if (ctx->secs[i].raw_data_size == 0) |
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continue; |
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ret = crypto_shash_update(desc, |
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pebuf + ctx->secs[i].data_addr, |
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ctx->secs[i].raw_data_size); |
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if (ret < 0) { |
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kfree(canon); |
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return ret; |
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} |
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hashed_bytes += ctx->secs[i].raw_data_size; |
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} |
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kfree(canon); |
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if (pelen > hashed_bytes) { |
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tmp = hashed_bytes + ctx->certs_size; |
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ret = crypto_shash_update(desc, |
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pebuf + hashed_bytes, |
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pelen - tmp); |
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if (ret < 0) |
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return ret; |
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} |
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return 0; |
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} |
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/* |
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* Digest the contents of the PE binary, leaving out the image checksum and the |
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* certificate data block. |
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*/ |
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static int pefile_digest_pe(const void *pebuf, unsigned int pelen, |
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struct pefile_context *ctx) |
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{ |
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struct crypto_shash *tfm; |
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struct shash_desc *desc; |
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size_t digest_size, desc_size; |
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void *digest; |
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int ret; |
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kenter(",%s", ctx->digest_algo); |
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/* Allocate the hashing algorithm we're going to need and find out how |
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* big the hash operational data will be. |
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*/ |
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tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0); |
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if (IS_ERR(tfm)) |
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return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm); |
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desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); |
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digest_size = crypto_shash_digestsize(tfm); |
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if (digest_size != ctx->digest_len) { |
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pr_debug("Digest size mismatch (%zx != %x)\n", |
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digest_size, ctx->digest_len); |
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ret = -EBADMSG; |
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goto error_no_desc; |
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} |
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pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size); |
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ret = -ENOMEM; |
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desc = kzalloc(desc_size + digest_size, GFP_KERNEL); |
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if (!desc) |
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goto error_no_desc; |
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desc->tfm = tfm; |
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ret = crypto_shash_init(desc); |
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if (ret < 0) |
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goto error; |
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ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc); |
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if (ret < 0) |
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goto error; |
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digest = (void *)desc + desc_size; |
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ret = crypto_shash_final(desc, digest); |
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if (ret < 0) |
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goto error; |
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pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest); |
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/* Check that the PE file digest matches that in the MSCODE part of the |
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* PKCS#7 certificate. |
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*/ |
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if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) { |
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pr_debug("Digest mismatch\n"); |
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ret = -EKEYREJECTED; |
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} else { |
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pr_debug("The digests match!\n"); |
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} |
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error: |
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kfree_sensitive(desc); |
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error_no_desc: |
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crypto_free_shash(tfm); |
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kleave(" = %d", ret); |
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return ret; |
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} |
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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_keys: Signing certificate(s) to use as starting points |
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* @usage: The use to which the key is being put. |
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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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* (*) -ENODATA if there is no signature present. |
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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_keys, |
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enum key_being_used_for usage) |
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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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ret = pefile_strip_sig_wrapper(pebuf, &ctx); |
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if (ret < 0) |
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return ret; |
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ret = verify_pkcs7_signature(NULL, 0, |
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pebuf + ctx.sig_offset, ctx.sig_len, |
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trusted_keys, usage, |
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mscode_parse, &ctx); |
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if (ret < 0) |
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goto error; |
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pr_debug("Digest: %u [%*ph]\n", |
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ctx.digest_len, ctx.digest_len, ctx.digest); |
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/* Generate the digest and check against the PKCS7 certificate |
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* contents. |
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*/ |
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ret = pefile_digest_pe(pebuf, pelen, &ctx); |
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error: |
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kfree_sensitive(ctx.digest); |
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return ret; |
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}
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