[PATCH v4] integrity: Always reference the blacklist keyring with appraisal

From: Eric Snowberg
Date: Wed Jul 26 2023 - 17:23:18 EST

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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@xxxxxxxxxx>
---
v4 changes:
Fixed typo
Also did some performance testing with this patch. With the associative array
implementation used within the keyring code, there doesn't seem to be much of a
difference between doing an appraisal with an empty blacklist keyring and one
containing 1500 entries. At this time it is unknown how many entries a user
would place in this keyring, but this seemed like a bigger number than most use
cases. With the 1500 entries, there were only 7 lookups to get through the
entire list for a file not contained within it. For something that was
on the list, there was an average of 4 lookups and a single string compare.
Based on this testing, IMHO, there could be a lot more entries added to the
blacklist keyring without any real performance issues.

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..c2385183826c 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 appraisal functions set it by default.
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);
+
+ 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;
}
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();
--
2.39.3

Next message: Nicolas Schier: "Re: [PATCH] samples/bpf: Update sockex2: get the expected output results"
Previous message: Winiarska, Iwona: "Re: [PATCH v2 1/4] dt-bindings: Add bindings for peci-npcm"
Next in thread: Mimi Zohar: "Re: [PATCH v4] integrity: Always reference the blacklist keyring with appraisal"
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