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pefile: Strip the wrapper off of the cert data block

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The certificate data block in a PE binary has a wrapper around the PKCS#7
signature we actually want to get at.  Strip this off and check that we've got
something that appears to be a PKCS#7 signature.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
David Howells 2014-07-01 16:02:51 +01:00
parent 26d1164be3
commit 09dacbbda9
1 changed files with 71 additions and 0 deletions
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71
crypto/asymmetric_keys/verify_pefile.c
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@ -15,6 +15,7 @@
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/pe.h>
#include <linux/asn1.h>
#include <crypto/pkcs7.h>
#include <crypto/hash.h>
#include "verify_pefile.h"
@ -118,6 +119,72 @@ static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
return 0;
}
/*
* Check and strip the PE wrapper from around the signature and check that the
* remnant looks something like PKCS#7.
*/
static int pefile_strip_sig_wrapper(const void *pebuf,
struct pefile_context *ctx)
{
struct win_certificate wrapper;
const u8 *pkcs7;
if (ctx->sig_len < sizeof(wrapper)) {
pr_debug("Signature wrapper too short\n");
return -ELIBBAD;
}
memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
pr_debug("sig wrapper = { %x, %x, %x }\n",
wrapper.length, wrapper.revision, wrapper.cert_type);
/* Both pesign and sbsign round up the length of certificate table
* (in optional header data directories) to 8 byte alignment.
*/
if (round_up(wrapper.length, 8) != ctx->sig_len) {
pr_debug("Signature wrapper len wrong\n");
return -ELIBBAD;
}
if (wrapper.revision != WIN_CERT_REVISION_2_0) {
pr_debug("Signature is not revision 2.0\n");
return -ENOTSUPP;
}
if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
pr_debug("Signature certificate type is not PKCS\n");
return -ENOTSUPP;
}
/* Looks like actual pkcs signature length is in wrapper->length.
* size obtained from data dir entries lists the total size of
* certificate table which is also aligned to octawrod boundary.
*
* So set signature length field appropriately.
*/
ctx->sig_len = wrapper.length;
ctx->sig_offset += sizeof(wrapper);
ctx->sig_len -= sizeof(wrapper);
if (ctx->sig_len == 0) {
pr_debug("Signature data missing\n");
return -EKEYREJECTED;
}
/* What's left should a PKCS#7 cert */
pkcs7 = pebuf + ctx->sig_offset;
if (pkcs7[0] == (ASN1_CONS_BIT | ASN1_SEQ)) {
if (pkcs7[1] == 0x82 &&
pkcs7[2] == (((ctx->sig_len - 4) >> 8) & 0xff) &&
pkcs7[3] == ((ctx->sig_len - 4) & 0xff))
return 0;
if (pkcs7[1] == 0x80)
return 0;
if (pkcs7[1] > 0x82)
return -EMSGSIZE;
}
pr_debug("Signature data not PKCS#7\n");
return -ELIBBAD;
}
/**
* verify_pefile_signature - Verify the signature on a PE binary image
* @pebuf: Buffer containing the PE binary image
@ -159,5 +226,9 @@ int verify_pefile_signature(const void *pebuf, unsigned pelen,
if (ret < 0)
return ret;
ret = pefile_strip_sig_wrapper(pebuf, &ctx);
if (ret < 0)
return ret;
return -ENOANO; // Not yet complete
}