From: Tyler Hicks <tyhicks@linux.microsoft.com>
Date: Thu, 9 Jul 2020 01:19:04 -0500
Subject: ima: Fail rule parsing when the KEXEC_CMDLINE hook is combined with
 an invalid cond
Patch-mainline: v5.9-rc1
Git-commit: db2045f5892a9db7354442bf77f9b03b50ff9ee1
References: jsc#SLE-15209

The KEXEC_CMDLINE hook function only supports the pcr conditional. Make
this clear at policy load so that IMA policy authors don't assume that
other conditionals are supported.

Since KEXEC_CMDLINE's inception, ima_match_rules() has always returned
true on any loaded KEXEC_CMDLINE rule without any consideration for
other conditionals present in the rule. Make it clear that pcr is the
only supported KEXEC_CMDLINE conditional by returning an error during
policy load.

An example of why this is a problem can be explained with the following
rule:

 dont_measure func=KEXEC_CMDLINE obj_type=foo_t

An IMA policy author would have assumed that rule is valid because the
parser accepted it but the result was that measurements for all
KEXEC_CMDLINE operations would be disabled.

Fixes: b0935123a183 ("IMA: Define a new hook to measure the kexec boot command line arguments")
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
 security/integrity/ima/ima_policy.c |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -345,6 +345,17 @@ static int ima_lsm_update_rule(struct im
 	return 0;
 }
 
+static bool ima_rule_contains_lsm_cond(struct ima_rule_entry *entry)
+{
+	int i;
+
+	for (i = 0; i < MAX_LSM_RULES; i++)
+		if (entry->lsm[i].args_p)
+			return true;
+
+	return false;
+}
+
 /*
  * The LSM policy can be reloaded, leaving the IMA LSM based rules referring
  * to the old, stale LSM policy.  Update the IMA LSM based rules to reflect
@@ -997,6 +1008,16 @@ static bool ima_validate_rule(struct ima
 		/* Validation of these hook functions is in ima_parse_rule() */
 		break;
 	case KEXEC_CMDLINE:
+		if (entry->action & ~(MEASURE | DONT_MEASURE))
+			return false;
+
+		if (entry->flags & ~(IMA_FUNC | IMA_PCR))
+			return false;
+
+		if (ima_rule_contains_lsm_cond(entry))
+			return false;
+
+		break;
 	case KEY_CHECK:
 		if (entry->action & ~(MEASURE | DONT_MEASURE))
 			return false;