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integrity: Always reference the blacklist keyring with appraisal

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Commit 273df864cf ("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>
Reviewed-by: Nayna Jain <nayna@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Eric Snowberg 2023-07-26 17:17:25 -04:00 committed by Mimi Zohar
parent 5087fd9e80
commit f20765fdfd
4 changed files with 19 additions and 24 deletions
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6
Documentation/ABI/testing/ima_policy
View file

@ -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 appraisal functions set it by default.
digest_type:= verity
Require fs-verity's file digest instead of the
regular IMA file hash.

8
arch/powerpc/kernel/ima_arch.c
View file

@ -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
};

12
security/integrity/ima/ima_appraise.c
View file

@ -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);
if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
"blacklisted-hash", NONE,
pcr, NULL, false, NULL, 0);
return rc;
}

17
security/integrity/ima/ima_policy.c
View file

@ -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();