[05/12] ima: Fail rule parsing when buffer hook functions have an invalid action
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Message ID 20200623003236.830149-6-tyhicks@linux.microsoft.com
State New
Headers show
Series
  • ima: Fix rule parsing bugs and extend KEXEC_CMDLINE rule support
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Commit Message

Tyler Hicks June 23, 2020, 12:32 a.m. UTC
Buffer based hook functions, such as KEXEC_CMDLINE and KEY_CHECK, can
only measure. The process_buffer_measurement() function quietly ignores
all actions except measure so make this behavior clear at the time of
policy load.

The parsing of the keyrings conditional had a check to ensure that it
was only specified with measure actions but the check should be on the
hook function and not the keyrings conditional since
"appraise func=KEY_CHECK" is not a valid rule.

Fixes: b0935123a183 ("IMA: Define a new hook to measure the kexec boot command line arguments")
Fixes: 5808611cccb2 ("IMA: Add KEY_CHECK func to measure keys")
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
---
 security/integrity/ima/ima_policy.c | 36 +++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

Comments

Mimi Zohar June 25, 2020, 9:51 p.m. UTC | #1
On Mon, 2020-06-22 at 19:32 -0500, Tyler Hicks wrote:
> Buffer based hook functions, such as KEXEC_CMDLINE and KEY_CHECK, can
> only measure. The process_buffer_measurement() function quietly ignores
> all actions except measure so make this behavior clear at the time of
> policy load.
> 
> The parsing of the keyrings conditional had a check to ensure that it
> was only specified with measure actions but the check should be on the
> hook function and not the keyrings conditional since
> "appraise func=KEY_CHECK" is not a valid rule.
> 
> Fixes: b0935123a183 ("IMA: Define a new hook to measure the kexec boot command line arguments")
> Fixes: 5808611cccb2 ("IMA: Add KEY_CHECK func to measure keys")
> Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> ---
>  security/integrity/ima/ima_policy.c | 36 +++++++++++++++++++++++++++--
>  1 file changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index ee5152ecd3d9..ecc234b956a2 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -979,6 +979,39 @@ static void check_template_modsig(const struct ima_template_desc *template)
>  #undef MSG
>  }
>  
> +static bool ima_validate_rule(struct ima_rule_entry *entry)
> +{
> +	if (entry->action == UNKNOWN)
> +		return false;
> +
> +	if (entry->flags & IMA_FUNC) {
> +		switch (entry->func) {
> +		case NONE:
> +		case FILE_CHECK:
> +		case MMAP_CHECK:
> +		case BPRM_CHECK:
> +		case CREDS_CHECK:
> +		case POST_SETATTR:
> +		case MODULE_CHECK:
> +		case FIRMWARE_CHECK:
> +		case KEXEC_KERNEL_CHECK:
> +		case KEXEC_INITRAMFS_CHECK:
> +		case POLICY_CHECK:
> +			break;
> +		case KEXEC_CMDLINE:
> +		case KEY_CHECK:
> +			if (entry->action & ~(MEASURE | DONT_MEASURE))
> +				return false;
> +
> +			break;
> +		default:
> +			return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +

Good idea.  There are a couple of other examples that could be cleaned
up as well.  For example, for performance reasons
"appraise_flag=check_blacklist" is limited to files with appended
signatures, like kernel modules and the kexec kernel image
(OpenPower).

Mimi

Patch
diff mbox series

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index ee5152ecd3d9..ecc234b956a2 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -979,6 +979,39 @@  static void check_template_modsig(const struct ima_template_desc *template)
 #undef MSG
 }
 
+static bool ima_validate_rule(struct ima_rule_entry *entry)
+{
+	if (entry->action == UNKNOWN)
+		return false;
+
+	if (entry->flags & IMA_FUNC) {
+		switch (entry->func) {
+		case NONE:
+		case FILE_CHECK:
+		case MMAP_CHECK:
+		case BPRM_CHECK:
+		case CREDS_CHECK:
+		case POST_SETATTR:
+		case MODULE_CHECK:
+		case FIRMWARE_CHECK:
+		case KEXEC_KERNEL_CHECK:
+		case KEXEC_INITRAMFS_CHECK:
+		case POLICY_CHECK:
+			break;
+		case KEXEC_CMDLINE:
+		case KEY_CHECK:
+			if (entry->action & ~(MEASURE | DONT_MEASURE))
+				return false;
+
+			break;
+		default:
+			return false;
+		}
+	}
+
+	return true;
+}
+
 static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 {
 	struct audit_buffer *ab;
@@ -1156,7 +1189,6 @@  static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			keyrings_len = strlen(args[0].from) + 1;
 
 			if ((entry->keyrings) ||
-			    (entry->action != MEASURE) ||
 			    (entry->func != KEY_CHECK) ||
 			    (keyrings_len < 2)) {
 				result = -EINVAL;
@@ -1362,7 +1394,7 @@  static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			break;
 		}
 	}
-	if (!result && (entry->action == UNKNOWN))
+	if (!result && !ima_validate_rule(entry))
 		result = -EINVAL;
 	else if (entry->action == APPRAISE)
 		temp_ima_appraise |= ima_appraise_flag(entry->func);