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>
Add OIDs for sha224, sha284 and sha512 hash algos and use them to select
the hashing algorithm. Without this, something like the following error
might get written to dmesg:
[ 31.829322] PKCS7: Unknown OID: [32] 2.16.840.1.101.3.4.2.3
[ 31.829328] PKCS7: Unknown OID: [180] 2.16.840.1.101.3.4.2.3
[ 31.829330] Unsupported digest algo: 55
Where the 55 on the third line is OID__NR indicating an unknown OID.
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: James Morris <james.l.morris@oracle.com>
A PKCS#7 or CMS message can have per-signature authenticated attributes
that are digested as a lump and signed by the authorising key for that
signature. If such attributes exist, the content digest isn't itself
signed, but rather it is included in a special authattr which then
contributes to the signature.
Further, we already require the master message content type to be
pkcs7_signedData - but there's also a separate content type for the data
itself within the SignedData object and this must be repeated inside the
authattrs for each signer [RFC2315 9.2, RFC5652 11.1].
We should really validate the authattrs if they exist or forbid them
entirely as appropriate. To this end:
(1) Alter the PKCS#7 parser to reject any message that has more than one
signature where at least one signature has authattrs and at least one
that does not.
(2) Validate authattrs if they are present and strongly restrict them.
Only the following authattrs are permitted and all others are
rejected:
(a) contentType. This is checked to be an OID that matches the
content type in the SignedData object.
(b) messageDigest. This must match the crypto digest of the data.
(c) signingTime. If present, we check that this is a valid, parseable
UTCTime or GeneralTime and that the date it encodes fits within
the validity window of the matching X.509 cert.
(d) S/MIME capabilities. We don't check the contents.
(e) Authenticode SP Opus Info. We don't check the contents.
(f) Authenticode Statement Type. We don't check the contents.
The message is rejected if (a) or (b) are missing. If the message is
an Authenticode type, the message is rejected if (e) is missing; if
not Authenticode, the message is rejected if (d) - (f) are present.
The S/MIME capabilities authattr (d) unfortunately has to be allowed
to support kernels already signed by the pesign program. This only
affects kexec. sign-file suppresses them (CMS_NOSMIMECAP).
The message is also rejected if an authattr is given more than once or
if it contains more than one element in its set of values.
(3) Add a parameter to pkcs7_verify() to select one of the following
restrictions and pass in the appropriate option from the callers:
(*) VERIFYING_MODULE_SIGNATURE
This requires that the SignedData content type be pkcs7-data and
forbids authattrs. sign-file sets CMS_NOATTR. We could be more
flexible and permit authattrs optionally, but only permit minimal
content.
(*) VERIFYING_FIRMWARE_SIGNATURE
This requires that the SignedData content type be pkcs7-data and
requires authattrs. In future, this will require an attribute
holding the target firmware name in addition to the minimal set.
(*) VERIFYING_UNSPECIFIED_SIGNATURE
This requires that the SignedData content type be pkcs7-data but
allows either no authattrs or only permits the minimal set.
(*) VERIFYING_KEXEC_PE_SIGNATURE
This only supports the Authenticode SPC_INDIRECT_DATA content type
and requires at least an SpcSpOpusInfo authattr in addition to the
minimal set. It also permits an SPC_STATEMENT_TYPE authattr (and
an S/MIME capabilities authattr because the pesign program doesn't
remove these).
(*) VERIFYING_KEY_SIGNATURE
(*) VERIFYING_KEY_SELF_SIGNATURE
These are invalid in this context but are included for later use
when limiting the use of X.509 certs.
(4) The pkcs7_test key type is given a module parameter to select between
the above options for testing purposes. For example:
echo 1 >/sys/module/pkcs7_test_key/parameters/usage
keyctl padd pkcs7_test foo @s </tmp/stuff.pkcs7
will attempt to check the signature on stuff.pkcs7 as if it contains a
firmware blob (1 being VERIFYING_FIRMWARE_SIGNATURE).
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: David Woodhouse <David.Woodhouse@intel.com>
Since CMS is an evolution of PKCS#7, with much of the ASN.1 being
compatible, add support for CMS signed-data messages also [RFC5652 sec 5].
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-By: David Woodhouse <David.Woodhouse@intel.com>
We only support PKCS#7 signed-data [RFC2315 sec 9] content at the top level,
so reject anything else. Further, check that the version numbers in
SignedData and SignerInfo are 1 in both cases.
Note that we don't restrict the inner content type. In the PKCS#7 code we
don't parse the data attached there, but merely verify the signature over
it.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-By: David Woodhouse <David.Woodhouse@intel.com>
Make use of the new match string preparsing to overhaul key identification
when searching for asymmetric keys. The following changes are made:
(1) Use the previously created asymmetric_key_id struct to hold the following
key IDs derived from the X.509 certificate or PKCS#7 message:
id: serial number + issuer
skid: subjKeyId + subject
authority: authKeyId + issuer
(2) Replace the hex fingerprint attached to key->type_data[1] with an
asymmetric_key_ids struct containing the id and the skid (if present).
(3) Make the asymmetric_type match data preparse select one of two searches:
(a) An iterative search for the key ID given if prefixed with "id:". The
prefix is expected to be followed by a hex string giving the ID to
search for. The criterion key ID is checked against all key IDs
recorded on the key.
(b) A direct search if the key ID is not prefixed with "id:". This will
look for an exact match on the key description.
(4) Make x509_request_asymmetric_key() take a key ID. This is then converted
into "id:<hex>" and passed into keyring_search() where match preparsing
will turn it back into a binary ID.
(5) X.509 certificate verification then takes the authority key ID and looks
up a key that matches it to find the public key for the certificate
signature.
(6) PKCS#7 certificate verification then takes the id key ID and looks up a
key that matches it to find the public key for the signed information
block signature.
Additional changes:
(1) Multiple subjKeyId and authKeyId values on an X.509 certificate cause the
cert to be rejected with -EBADMSG.
(2) The 'fingerprint' ID is gone. This was primarily intended to convey PGP
public key fingerprints. If PGP is supported in future, this should
generate a key ID that carries the fingerprint.
(3) Th ca_keyid= kernel command line option is now converted to a key ID and
used to match the authority key ID. Possibly this should only match the
actual authKeyId part and not the issuer as well.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Fix the parser cleanup code to drain parsed out X.509 certs in the case that
the decode fails and we jump to error_decode.
The function is rearranged so that the same cleanup code is used in the success
case as the error case - just that the message descriptor under construction is
only released if it is still pointed to by the context struct at that point.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
The code to free a signed info block is repeated several times, so move the
code to do it into a function of its own. This gives us a place to add clean
ups for stuff that gets added to pkcs7_signed_info.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Implement a parser for a PKCS#7 signed-data message as described in part of
RFC 2315.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Peter Jones