ima: Fail rule parsing when the KEXEC_CMDLINE hook is combined with an invalid cond

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>

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 40c28f1..1c64bd6 100644 (file)
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -343,6 +343,17 @@ static int ima_lsm_update_rule(struct ima_rule_entry *entry)
        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
@@ -998,6 +1009,16 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
                /* 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;