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Bug 2063838

Summary: Mishandling of CMS_verify() errors in PKINIT plugin
Product: Red Hat Enterprise Linux 9 Reporter: Julien Rische <jrische>
Component: krb5Assignee: Julien Rische <jrische>
Status: CLOSED ERRATA QA Contact: Filip Dvorak <fdvorak>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 9.0CC: fdvorak
Target Milestone: rcKeywords: Triaged
Target Release: ---Flags: pm-rhel: mirror+
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: krb5-1.20.1-3.el9 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of:
: 2119704 (view as bug list) Environment:
Last Closed: 2023-05-09 08:25:24 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 2119704    

Description Julien Rische 2022-03-14 13:48:43 UTC 
The signature verification part of the krb5 PKINIT plugin was initially implemented using PKCS7_verify[1], and error handling was written according to this function[2].

This code was modified[3] to use CMS_verify[4] when building against >= OpenSSL 1.0, but kept PKCS7_verify error codes handling.

As a consequence, the KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error, which should explain the digest algorithm is not support is no raised and an unrelated error is displayed:

"Failed to verify CMS message: content type not enveloped data"

Actual CMS_verify error codes should be handled.

[1] https://www.openssl.org/docs/man3.0/man3/PKCS7_verify.html
[2] https://github.com/krb5/krb5/blob/0ef0646069c1d1376aa632a4791ea7e429f5ae9b/src/plugins/preauth/pkinit/pkinit_crypto_openssl.c#L1290-L1297
[3] https://github.com/krb5/krb5/commit/1b57e7650da41dbef6a50c6e925583d6c8ed9e52#diff-4aab62556d7562101df00d240f5444ed99a48a8e00d06c57a9bf5cb29b8a1ea8R1395
[4] https://www.openssl.org/docs/man3.0/man3/CMS_verify.html
Comment 1 Julien Rische 2022-07-29 15:51:59 UTC 
There are 2 points to fix:

  * Error codes have to be modified to match the new function.
  * The last error from OpenSSL stack should be picked rather that the first one which is always CMS_R_CONTENT_TYPE_NOT_ENVELOPED_DATA[1], therefore it does not allow to differentiate an error caused by an unaccepted digest algorithm and an invalid signature.

The error code we could expect based on the code of OpenSSL CMS signature verification are:

  * CMS_R_NO_MATCHING_DIGEST[2]
  * CMS_R_NO_MATCHING_SIGNATURE (not used in practice)
  * CMS_R_UNKNOWN_DIGEST_ALGORITHM[3]

But I've run some tests and the error codes that seems to be actually raised are:

  * EVP_R_INVALID_DIGEST: the OID is recognized the algorithm is not allowed by the policy in signature verification
  * RSA_R_DIGEST_NOT_ALLOWED: OpenSSL fails to infer a signature algorithm based on the digest one and the key type (the more generic code PROV_R_DIGEST_NOT_ALLOWED might be considered too)
  * CMS_R_VERIFICATION_FAILURE: signature verification failed

We should use ERR_peek_last_error()[4] instead of ERR_peek_error() in order to get these error codes.


[1] https://github.com/openssl/openssl/blob/openssl-3.0.1/crypto/cms/cms_err.c#L45-L46
[2] https://github.com/openssl/openssl/blob/openssl-3.0.1/crypto/cms/cms_lib.c#L458
[3] https://github.com/openssl/openssl/blob/openssl-3.0.1/crypto/cms/cms_sd.c#L869
[4] https://www.openssl.org/docs/man3.0/man3/ERR_peek_last_error.html
Comment 2 Julien Rische 2022-08-02 07:40:20 UTC 
Pull request:
https://github.com/krb5/krb5/pull/1264
Comment 3 Julien Rische 2022-08-19 08:47:10 UTC 
EVP_R_INVALID_DIGEST is actually raised by code in a downstream OpenSSL patch[1]. I will handle it in a krb5 downstream patch too.

[1] https://src.fedoraproject.org/rpms/openssl/blob/rawhide/f/0049-Allow-disabling-of-SHA1-signatures.patch#_217
Comment 18 errata-xmlrpc 2023-05-09 08:25:24 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Moderate: krb5 security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2023:2570