Re: [PATCH v3 07/12] ima: Fail rule parsing when appraise_flag=blacklist is unsupportable

On 2020-07-17 13:40:22, Nayna wrote:

quoted

On 7/9/20 2:19 AM, Tyler Hicks wrote:

quoted

The "appraise_flag" option is only appropriate for appraise actions
and its "blacklist" value is only appropriate when
CONFIG_IMA_APPRAISE_MODSIG is enabled and "appraise_flag=blacklist" is
only appropriate when "appraise_type=imasig|modsig" is also present.
Make this clear at policy load so that IMA policy authors don't assume
that other uses of "appraise_flag=blacklist" are supported.

Fixes: 273df864cf74 ("ima: Check against blacklisted hashes for files with modsig")
Signed-off-by: Tyler Hicks <redacted>
Cc: Nayna Jain <nayna@linux.ibm.com>
---

* v3
    - New patch

   security/integrity/ima/ima_policy.c | 13 ++++++++++++-
   1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 81da02071d41..9842e2e0bc6d 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c

@@ -1035,6 +1035,11 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
   		return false;
   	}
+	/* Ensure that combinations of flags are compatible with each other */
+	if (entry->flags & IMA_CHECK_BLACKLIST &&
+	    !(entry->flags & IMA_MODSIG_ALLOWED))
+		return false;
+
   	return true;
   }

@@ -1371,8 +1376,14 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
   				result = -EINVAL;
   			break;
   		case Opt_appraise_flag:
+			if (entry->action != APPRAISE) {
+				result = -EINVAL;
+				break;
+			}
+
   			ima_log_string(ab, "appraise_flag", args[0].from);
-			if (strstr(args[0].from, "blacklist"))
+			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
+			    strstr(args[0].from, "blacklist"))
   				entry->flags |= IMA_CHECK_BLACKLIST;

If IMA_APPRAISE_MODSIG is disabled, it will allow the following rule to
load, which is not as expected.

"appraise func=xxx_CHECK appraise_flag=blacklist appraise_type=imasig"

Missing is the "else" condition to immediately reject the policy rule.

Thanks for the review. You're right. This change is needed:

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 9842e2e0bc6d..cf3ddb38dfa8 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c

@@ -1385,6 +1385,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
  			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
  			    strstr(args[0].from, "blacklist"))
  				entry->flags |= IMA_CHECK_BLACKLIST;
+			else
+				result = -EINVAL;
  			break;
  		case Opt_permit_directio:
  			entry->flags |= IMA_PERMIT_DIRECTIO;