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Message-ID: <ecbf405c6806fa4706051e0bf946d742f3442367.camel@huaweicloud.com>
Subject: Re: [PATCH v3] integrity: Always reference the blacklist keyring
 with apprasial
From:   Roberto Sassu <roberto.sassu@huaweicloud.com>
To:     Eric Snowberg <eric.snowberg@oracle.com>, zohar@linux.ibm.com
Cc:     dmitry.kasatkin@gmail.com, paul@paul-moore.com, jmorris@namei.org,
        serge@hallyn.com, roberto.sassu@huawei.com,
        kanth.ghatraju@oracle.com, konrad.wilk@oracle.com,
        linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org
Date:   Fri, 14 Jul 2023 09:22:25 +0200
In-Reply-To: <20230714011141.2288133-1-eric.snowberg@oracle.com>
References: <20230714011141.2288133-1-eric.snowberg@oracle.com>
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On Thu, 2023-07-13 at 21:11 -0400, Eric Snowberg wrote:
> Commit 273df864cf746 ("ima: Check against blacklisted hashes for files with
> modsig") introduced an appraise_flag option for referencing the blacklist
> keyring.  Any matching binary found on this keyring fails signature
> validation. This flag only works with module appended signatures.
> 
> An important part of a PKI infrastructure is to have the ability to do
> revocation at a later time should a vulnerability be found.  Expand the
> revocation flag usage to all appraisal functions. The flag is now
> enabled by default. Setting the flag with an IMA policy has been
> deprecated. Without a revocation capability like this in place, only
> authenticity can be maintained. With this change, integrity can now be
> achieved with digital signature based IMA appraisal.
> 
> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
> ---
> v3 changes:
>   No longer display appraise_flag=check_blacklist in the policy
> v2 changes:
>   Update the "case Opt_apprase_flag"
>   Removed "appraise_flag=" in the powerpc arch specific policy rules
> ---
>  Documentation/ABI/testing/ima_policy  |  6 +++---
>  arch/powerpc/kernel/ima_arch.c        |  8 ++++----
>  security/integrity/ima/ima_appraise.c | 12 +++++++-----
>  security/integrity/ima/ima_policy.c   | 17 +++++------------
>  4 files changed, 19 insertions(+), 24 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 49db0ff288e5..a712c396f6e9 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -57,9 +57,9 @@ Description:
>  				stored in security.ima xattr. Requires
>  				specifying "digest_type=verity" first.)
>  
> -			appraise_flag:= [check_blacklist]
> -			Currently, blacklist check is only for files signed with appended
> -			signature.
> +			appraise_flag:= [check_blacklist] (deprecated)
> +			Setting the check_blacklist flag is no longer necessary.
> +			All apprasial functions set it by default.

Typo.

>  			digest_type:= verity
>  			    Require fs-verity's file digest instead of the
>  			    regular IMA file hash.
> diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
> index 957abd592075..b7029beed847 100644
> --- a/arch/powerpc/kernel/ima_arch.c
> +++ b/arch/powerpc/kernel/ima_arch.c
> @@ -23,9 +23,9 @@ bool arch_ima_get_secureboot(void)
>   * is not enabled.
>   */
>  static const char *const secure_rules[] = {
> -	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
>  #ifndef CONFIG_MODULE_SIG
> -	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=MODULE_CHECK appraise_type=imasig|modsig",
>  #endif
>  	NULL
>  };
> @@ -49,9 +49,9 @@ static const char *const trusted_rules[] = {
>  static const char *const secure_and_trusted_rules[] = {
>  	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
>  	"measure func=MODULE_CHECK template=ima-modsig",
> -	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
>  #ifndef CONFIG_MODULE_SIG
> -	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=MODULE_CHECK appraise_type=imasig|modsig",
>  #endif
>  	NULL
>  };
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 491c1aca0b1c..870dde67707b 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -458,11 +458,13 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
>  		ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
>  
>  		rc = is_binary_blacklisted(digest, digestsize);
> -		if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> -			process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
> -						   "blacklisted-hash", NONE,
> -						   pcr, NULL, false, NULL, 0);
> -	}
> +	} else if (iint->flags & IMA_DIGSIG_REQUIRED && iint->ima_hash)
> +		rc = is_binary_blacklisted(iint->ima_hash->digest, iint->ima_hash->length);

Curiosity (I didn't read the previous discussions), if you are checking
if binaries are blacklisted, why not doing for the BPRM_CHECK hook?

> +
> +	if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))

Uhm, the measurement will be done only if you are also doing appraisal
with digital signatures. But if you have only measure rules, you won't
know. Shouldn't you run is_binary_blacklisted() also for measure rules?

Thanks

Roberto

> +		process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
> +					   "blacklisted-hash", NONE,
> +					   pcr, NULL, false, NULL, 0);
>  
>  	return rc;
>  }
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index c9b3bd8f1bb9..69452b79686b 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -1280,7 +1280,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>  				     IMA_FSNAME | IMA_GID | IMA_EGID |
>  				     IMA_FGROUP | IMA_DIGSIG_REQUIRED |
>  				     IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS |
> -				     IMA_VERITY_REQUIRED))
> +				     IMA_CHECK_BLACKLIST | IMA_VERITY_REQUIRED))
>  			return false;
>  
>  		break;
> @@ -1355,7 +1355,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>  
>  	/* Ensure that combinations of flags are compatible with each other */
>  	if (entry->flags & IMA_CHECK_BLACKLIST &&
> -	    !(entry->flags & IMA_MODSIG_ALLOWED))
> +	    !(entry->flags & IMA_DIGSIG_REQUIRED))
>  		return false;
>  
>  	/*
> @@ -1803,11 +1803,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  				if (entry->flags & IMA_VERITY_REQUIRED)
>  					result = -EINVAL;
>  				else
> -					entry->flags |= IMA_DIGSIG_REQUIRED;
> +					entry->flags |= IMA_DIGSIG_REQUIRED | IMA_CHECK_BLACKLIST;
>  			} else if (strcmp(args[0].from, "sigv3") == 0) {
>  				/* Only fsverity supports sigv3 for now */
>  				if (entry->flags & IMA_VERITY_REQUIRED)
> -					entry->flags |= IMA_DIGSIG_REQUIRED;
> +					entry->flags |= IMA_DIGSIG_REQUIRED | IMA_CHECK_BLACKLIST;
>  				else
>  					result = -EINVAL;
>  			} else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
> @@ -1816,18 +1816,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  					result = -EINVAL;
>  				else
>  					entry->flags |= IMA_DIGSIG_REQUIRED |
> -						IMA_MODSIG_ALLOWED;
> +						IMA_MODSIG_ALLOWED | IMA_CHECK_BLACKLIST;
>  			} else {
>  				result = -EINVAL;
>  			}
>  			break;
>  		case Opt_appraise_flag:
>  			ima_log_string(ab, "appraise_flag", args[0].from);
> -			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
> -			    strstr(args[0].from, "blacklist"))
> -				entry->flags |= IMA_CHECK_BLACKLIST;
> -			else
> -				result = -EINVAL;
>  			break;
>  		case Opt_appraise_algos:
>  			ima_log_string(ab, "appraise_algos", args[0].from);
> @@ -2271,8 +2266,6 @@ int ima_policy_show(struct seq_file *m, void *v)
>  	}
>  	if (entry->flags & IMA_VERITY_REQUIRED)
>  		seq_puts(m, "digest_type=verity ");
> -	if (entry->flags & IMA_CHECK_BLACKLIST)
> -		seq_puts(m, "appraise_flag=check_blacklist ");
>  	if (entry->flags & IMA_PERMIT_DIRECTIO)
>  		seq_puts(m, "permit_directio ");
>  	rcu_read_unlock();