linux/crypto/asymmetric_keys
Peter Jones 7ee7014d0e PKCS#7: Don't require SpcSpOpusInfo in Authenticode pkcs7 signatures
Dave Young reported:
> Hi,
>
> I saw the warning "Missing required AuthAttr" when testing kexec,
> known issue?  Idea about how to fix it?
>
> The kernel is latest linus tree plus sevral patches from Toshi to
> cleanup io resource structure.
>
> in function pkcs7_sig_note_set_of_authattrs():
>         if (!test_bit(sinfo_has_content_type, &sinfo->aa_set) ||
>             !test_bit(sinfo_has_message_digest, &sinfo->aa_set) ||
>             (ctx->msg->data_type == OID_msIndirectData &&
>              !test_bit(sinfo_has_ms_opus_info, &sinfo->aa_set))) {
>                 pr_warn("Missing required AuthAttr\n");
>                 return -EBADMSG;
>         }
>
> The third condition below is true:
> (ctx->msg->data_type == OID_msIndirectData &&
>              !test_bit(sinfo_has_ms_opus_info, &sinfo->aa_set))
>
> I signed the kernel with redhat test key like below:
> pesign -c 'Red Hat Test Certificate' -i arch/x86/boot/bzImage -o /boot/vmlinuz-4.4.0-rc8+ -s --force

And right he is!  The Authenticode specification is a paragon amongst
technical documents, and has this pearl of wisdom to offer:

---------------------------------
Authenticode-Specific SignerInfo UnauthenticatedAttributes Structures

  The following Authenticode-specific data structures are present in
  SignerInfo authenticated attributes.

  SpcSpOpusInfo
  SpcSpOpusInfo is identified by SPC_SP_OPUS_INFO_OBJID
  (1.3.6.1.4.1.311.2.1.12) and is defined as follows:
  SpcSpOpusInfo ::= SEQUENCE {
    programName  [0] EXPLICIT SpcString OPTIONAL,
    moreInfo     [1] EXPLICIT SpcLink OPTIONAL,
  } --#public--

  SpcSpOpusInfo has two fields:
    programName
      This field contains the program description:
      If publisher chooses not to specify a description, the SpcString
      structure contains a zero-length program name.
      If the publisher chooses to specify a
      description, the SpcString structure contains a Unicode string.
    moreInfo
      This field is set to an SPCLink structure that contains a URL for
      a Web site with more information about the signer. The URL is an
      ASCII string.
---------------------------------

Which is to say that this is an optional *unauthenticated* field which
may be present in the Authenticated Attribute list.  This is not how
pkcs7 is supposed to work, so when David implemented this, he didn't
appreciate the subtlety the original spec author was working with, and
missed the part of the sublime prose that says this Authenticated
Attribute is an Unauthenticated Attribute.  As a result, the code in
question simply takes as given that the Authenticated Attributes should
be authenticated.

But this one should not, individually.  Because it says it's not
authenticated.

It still has to hash right so the TBS digest is correct.  So it is both
authenticated and unauthenticated, all at once.  Truly, a wonder of
technical accomplishment.

Additionally, pesign's implementation has always attempted to be
compatible with the signatures emitted from contemporary versions of
Microsoft's signtool.exe.  During the initial implementation, Microsoft
signatures always produced the same values for SpcSpOpusInfo -
{U"Microsoft Windows", "http://www.microsoft.com"} - without regard to
who the signer was.

Sometime between Windows 8 and Windows 8.1 they stopped including the
field in their signatures altogether, and as such pesign stopped
producing them in commits c0c4da6 and d79cb0c, sometime around June of
2012.  The theory here is that anything that breaks with
pesign signatures would also be breaking with signtool.exe sigs as well,
and that'll be a more noticed problem for firmwares parsing it, so it'll
get fixed.  The fact that we've done exactly this bug in Linux code is
first class, grade A irony.

So anyway, we should not be checking this field for presence or any
particular value: if the field exists, it should be at the right place,
but aside from that, as long as the hash matches the field is good.

Signed-off-by: Peter Jones <pjones@redhat.com>
Tested-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2016-01-25 21:47:45 +08:00
..
.gitignore X.509: Add a crypto key parser for binary (DER) X.509 certificates 2012-10-08 13:50:22 +10:30
asymmetric_keys.h KEYS: Merge the type-specific data with the payload data 2015-10-21 15:18:36 +01:00
asymmetric_type.c KEYS: Merge the type-specific data with the payload data 2015-10-21 15:18:36 +01:00
Kconfig Merge branch 'keys-fixes' into keys-next 2014-07-22 21:55:45 +01:00
Makefile X.509: Extract both parts of the AuthorityKeyIdentifier 2015-08-07 16:26:13 +01:00
mscode_parser.c PKCS#7: Add OIDs for sha224, sha284 and sha512 hash algos and use them 2015-09-01 09:59:20 +10:00
mscode.asn1 pefile: Parse the "Microsoft individual code signing" data blob 2014-07-09 14:58:37 +01:00
pkcs7_key_type.c PKCS#7: Add MODULE_LICENSE() to test module 2015-08-13 02:51:33 +01:00
pkcs7_parser.c PKCS#7: Don't require SpcSpOpusInfo in Authenticode pkcs7 signatures 2016-01-25 21:47:45 +08:00
pkcs7_parser.h PKCS#7: Appropriately restrict authenticated attributes and content type 2015-08-12 17:01:01 +01:00
pkcs7_trust.c X.509: Support X.509 lookup by Issuer+Serial form AuthorityKeyIdentifier 2015-08-07 16:26:13 +01:00
pkcs7_verify.c crypto: pkcs7 - Fix unaligned access in pkcs7_verify() 2015-10-14 22:23:38 +08:00
pkcs7.asn1 PKCS#7: Appropriately restrict authenticated attributes and content type 2015-08-12 17:01:01 +01:00
public_key.c KEYS: Merge the type-specific data with the payload data 2015-10-21 15:18:36 +01:00
public_key.h KEYS: Split public_key_verify_signature() and make available 2013-09-25 17:17:00 +01:00
rsa.c crypto: asymmetric_keys/rsa - Use non-conflicting variable name 2015-06-25 23:18:33 +08:00
signature.c crypto: asymmetric_keys - signature.c does not need <module.h> 2015-12-11 22:55:19 +08:00
verify_pefile.c PKCS#7: Appropriately restrict authenticated attributes and content type 2015-08-12 17:01:01 +01:00
verify_pefile.h pefile: Parse the "Microsoft individual code signing" data blob 2014-07-09 14:58:37 +01:00
x509_akid.asn1 X.509: Extract both parts of the AuthorityKeyIdentifier 2015-08-07 16:26:13 +01:00
x509_cert_parser.c X.509: Fix the time validation [ver ] 2015-11-12 21:17:15 +11:00
x509_parser.h KEYS: Merge the type-specific data with the payload data 2015-10-21 15:18:36 +01:00
x509_public_key.c IMA: create machine owner and blacklist keyrings 2015-12-15 10:01:43 -05:00
x509_rsakey.asn1 X.509: Add a crypto key parser for binary (DER) X.509 certificates 2012-10-08 13:50:22 +10:30
x509.asn1 X.509: Add bits needed for PKCS#7 2014-07-01 16:40:19 +01:00