Commit db2045f5 authored Jul 09, 2020 by Tyler Hicks Committed by Mimi Zohar Jul 16, 2020

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: b0935123 ("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>

parent 71218343

security/integrity/ima/ima_policy.c

+21 −0

Original line number	Diff line number	Diff line
		@@ -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;

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