Add ima_policy_check.awk and ima_policy_check.test

Add ima_policy_check.awk to check for possible overlapping of a rule being
added by a test with the existing IMA policy (policy replacement by IMA at
the first policy load is not taken into account).

ima_policy_check.awk expects as input the rule to be added, followed by the
IMA policy.

It returns a bit mask with the following values:
- 1: invalid new rule;
- 2: overlap of the new rule with an existing rule in the IMA policy;
- 4: new rule exists in the IMA policy.

Values can be individually checked by the test executing the awk script, to
determine what to do (abort loading, print a warning in case of overlap,
avoid adding an existing rule).

The bit mask allows the test to see multiple statements regarding the new
rule. For example, if the test added anyway an overlapping rule, it could
also see that the policy already contains it at the next test execution,
and does not add it again.

Since ima_policy_check.awk uses GNU extensions (such as the or() function,
or the fourth argument of split()), add gawk as dependency for the CI.

Finally add ima_policy_check.test, to ensure that the awk script behaves as
expected.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

ci/alpine.sh

@@ -45,7 +45,8 @@ apk add \
 	util-linux \
 	wget \
 	which \
-	xxd
+	xxd \
+	gawk
 
 if [ ! "$TSS" ]; then
 	apk add git

ci/debian.sh

@@ -53,7 +53,8 @@ $apt \
 	sudo \
 	util-linux \
 	wget \
-	xsltproc
+	xsltproc \
+	gawk
 
 $apt xxd || $apt vim-common
 $apt libengine-gost-openssl1.1$ARCH || true

ci/tumbleweed.sh

@@ -42,7 +42,8 @@ zypper --non-interactive install --force-resolution --no-recommends \
 	vim \
 	wget \
 	which \
-	xsltproc
+	xsltproc \
+	gawk
 
 zypper --non-interactive install --force-resolution --no-recommends \
 	gnutls openssl-engine-libp11 softhsm || true

tests/Makefile.am

@@ -2,7 +2,7 @@ check_SCRIPTS =
 TESTS = $(check_SCRIPTS)
 
 check_SCRIPTS += ima_hash.test sign_verify.test boot_aggregate.test \
-		 fsverity.test portable_signatures.test
+		 fsverity.test portable_signatures.test ima_policy_check.test
 
 .PHONY: check_logs
 check_logs:

tests/ima_policy_check.awk

@@ -0,0 +1,211 @@
+#! /usr/bin/gawk -f
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2023 Roberto Sassu <roberto.sassu@huawei.com>
+#
+# Check a new rule against the loaded IMA policy.
+#
+# Documentation/ABI/testing/ima_policy (Linux kernel)
+# base:	[[func=] [mask=] [fsmagic=] [fsuuid=] [fsname=]
+#	[uid=] [euid=] [gid=] [egid=]
+#	[fowner=] [fgroup=]]
+# lsm:	[[subj_user=] [subj_role=] [subj_type=]
+#	[obj_user=] [obj_role=] [obj_type=]]
+# option:	[digest_type=] [template=] [permit_directio]
+#		[appraise_type=] [appraise_flag=]
+#		[appraise_algos=] [keyrings=]
+#
+# Rules don't overlap if their actions are unrelated (cannot be matched without
+# dont_) and there is no combination of appraise with another do action (e.g.
+# measure, audit, hash). The second condition is due to the fact that appraise
+# might still forbid other actions expected to be performed by a test that did
+# not setup appraisal. Checking appraise for new rules is not sufficient,
+# because that rule could be added anyway. By checking existing rules as well,
+# a warning will be displayed when tests inserting rules with other do actions
+# are reexecuted.
+#
+# Also, rules don't overlap if both include the same policy keyword(s) (in base
+# or lsm, except func), at least one, with a different value. Different func
+# values don't imply non-overlap, due to the fact that a test command might
+# cause the execution of multiple hooks (e.g. FILE_CHECK in addition to
+# MMAP_CHECK). Despite one test is willing to test a particular hook, this could
+# have side effects on other tests (e.g. one test sets: appraise func=MMAP_CHECK
+# and another: measure func=FILE_CHECK; the second test might see an unexpected
+# measurement due to the first test being executed; or the second test cannot
+# unexpectedly do mmap).
+#
+# Currently, the < > operators are not supported and overlapping is asserted
+# even if intervals are disjoint. If supported, non-overlapping conditions could
+# be found. With the ^ modifier, no disjoint intervals can be found. Overlapping
+# is always reported.
+#
+# Rule equivalence is determined by checking each key/value pair, regardless of
+# their order. However, the action must always be at the beginning of the rules.
+# Rules with aliases are considered equivalent to those with their source (e.g.
+# rules with PATH_CHECK and FILE_MMAP are considered as equivalent to rules with
+# FILE_CHECK and MMAP_CHECK).
+#
+# Return a bit mask with the following values:
+# - 1: invalid new rule;
+# - 2: overlap of the new rule with an existing rule in the IMA policy;
+# - 4: new rule exists in the IMA policy.
+
+BEGIN {
+	# Policy definitions.
+	actions_str="measure dont_measure appraise dont_appraise audit hash dont_hash"
+	split(actions_str, actions_array);
+	keywords_str="func mask fsmagic fsuuid fsname uid euid gid egid fowner fgroup subj_user subj_role subj_type obj_user obj_role obj_type";
+	split(keywords_str, keywords_array);
+	options_str="digest_type template permit_directio appraise_type appraise_flag appraise_algos keyrings";
+	split(options_str, options_array);
+
+	# Key types.
+	key_type_unknown=0;
+	key_type_action=1;
+	key_type_keyword=2;
+	key_type_option=3;
+
+	# Result values.
+	ret_invalid_rule=1;
+	ret_rule_overlap=2;
+	ret_same_rule_exists=4;
+
+	for (action_idx in actions_array)
+		key_types[actions_array[action_idx]]=key_type_action;
+	for (keyword_idx in keywords_array)
+		key_types[keywords_array[keyword_idx]]=key_type_keyword;
+	for (option_idx in options_array)
+		key_types[options_array[option_idx]]=key_type_option;
+
+	new_rule=1;
+	result=0;
+}
+{
+	# Delete arrays from previous rule.
+	if (!new_rule) {
+		delete current_rule_array;
+		delete current_rule_operator_array;
+	}
+
+	# Check empty rules.
+	if (!length($0)) {
+		if (new_rule) {
+			result=or(result, ret_invalid_rule);
+			exit;
+		}
+		next;
+	}
+
+	for (i=1; i<=NF; i++) {
+		# Parse key/value pair.
+		split($i, key_value_array, /[=,>,<]/, separator_array);
+		key=key_value_array[1];
+		value=key_value_array[2];
+
+		if (key == "func") {
+			# Normalize values of IMA hooks to what IMA will print.
+			if (value == "FILE_MMAP")
+				value="MMAP_CHECK";
+			else if (value == "PATH_CHECK")
+				value="FILE_CHECK";
+		}
+
+		# Basic validity check (not necessary in general for the IMA policy, but useful to find typos in the tests).
+		if (key_types[key] == key_type_unknown ||
+		    (i == 1 && key_types[key] != key_type_action)) {
+			result=or(result, ret_invalid_rule);
+			exit;
+		}
+
+		# Store key/value pair and operator into an array.
+		if (new_rule) {
+			new_rule_array[key]=value;
+			new_rule_operator_array[key]=separator_array[1];
+		} else {
+			current_rule_array[key]=value;
+			current_rule_operator_array[key]=separator_array[1];
+		}
+
+		# Store original action and action without dont_.
+		if (i == 1) {
+			if (new_rule) {
+				new_rule_action=key;
+				new_rule_action_sub=key;
+				gsub(/dont_/, "", new_rule_action_sub);
+			} else {
+				current_rule_action=key;
+				current_rule_action_sub=key;
+				gsub(/dont_/, "", current_rule_action_sub);
+			}
+		}
+	}
+
+	# Go to the next line, to compare the new rule with rules in the IMA policy.
+	if (new_rule) {
+		new_rule=0;
+		next;
+	}
+
+	# No overlap by action (unrelated rules and no combination appraise - <do action>), new rule safe to add to the IMA policy.
+	if (current_rule_action_sub != new_rule_action_sub &&
+	    (current_rule_action != "appraise" || new_rule_action ~ /^dont_/) &&
+	    (new_rule_action != "appraise" || current_rule_action ~ /^dont_/))
+		next;
+
+	same_rule=1;
+	overlap_rule=1;
+
+	for (key in key_types) {
+		if (!(key in new_rule_array)) {
+			# Key in current rule but not in new rule.
+			if (key in current_rule_array)
+				same_rule=0;
+			# Key not in new rule and not in current rule.
+			continue;
+		}
+
+		if (!(key in current_rule_array)) {
+			# Key in new rule but not in current rule.
+			if (key in new_rule_array)
+				same_rule=0;
+			# Key not in current rule and not in new rule.
+			continue;
+		}
+
+		# Same value and operator.
+		if (new_rule_array[key] == current_rule_array[key] &&
+		    new_rule_operator_array[key] == current_rule_operator_array[key])
+			continue;
+
+		# Different value and/or operator.
+		same_rule=0;
+
+		# Not a policy keyword, not useful to determine overlap.
+		if (key_types[key] != key_type_keyword)
+			continue;
+
+		# > < operators are not supported, cannot determine overlap.
+		if (new_rule_operator_array[key] != "=" || current_rule_operator_array[key] != "=")
+			continue;
+
+		# ^ modifier does not make disjoint sets, cannot determine overlap.
+		if (new_rule_array[key] ~ /^\^/ || current_rule_array[key] ~ /^\^/)
+			continue;
+
+		# One test command can invoke multiple hooks, cannot determine overlap from func.
+		if (key == "func")
+			continue;
+
+		# No overlap by policy keyword, new rule safe to add to the IMA policy.
+		overlap_rule=0;
+		next;
+	}
+
+	if (same_rule)
+		result=or(result, ret_same_rule_exists);
+	else if (overlap_rule)
+		result=or(result, ret_rule_overlap);
+}
+END {
+	exit result;
+}

tests/ima_policy_check.test

@@ -0,0 +1,245 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2023 Roberto Sassu <roberto.sassu@huawei.com>
+#
+# Test for ima_policy_check.awk
+
+trap '_report_exit_and_cleanup' SIGINT SIGTERM EXIT
+
+cd "$(dirname "$0")" || exit 1
+. ./functions.sh
+
+export PATH=$PWD:$PATH
+
+check_result() {
+	local result
+
+	echo -e "\nTest: $1"
+	echo "New rule: $2"
+	echo "IMA policy: $3"
+
+	echo -n "Result (expect $4): "
+
+	echo -e "$2\n$3" | ima_policy_check.awk
+	result=$?
+
+	if [ "$result" -ne "$4" ]; then
+		echo "${RED}$result${NORM}"
+		return "$FAIL"
+	fi
+
+	echo "${GREEN}$result${NORM}"
+	return "$OK"
+}
+
+# ima_policy_check.awk returns a bit mask with the following values:
+# - 1: invalid new rule;
+# - 2: overlap of the new rule with an existing rule in the IMA policy;
+# - 4: new rule exists in the IMA policy.
+
+# Basic checks.
+desc="empty IMA policy"
+rule="measure func=FILE_CHECK"
+ima_policy=""
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Empty new rule"
+rule=""
+ima_policy=""
+expect_pass check_result "$desc" "$rule" "$ima_policy" 1
+
+desc="Unknown policy keyword fun"
+rule="measure fun=FILE_CHECK"
+ima_policy=""
+expect_pass check_result "$desc" "$rule" "$ima_policy" 1
+
+desc="Missing action"
+rule="func=FILE_CHECK"
+ima_policy=""
+expect_pass check_result "$desc" "$rule" "$ima_policy" 1
+
+# Non-overlapping rules.
+desc="Non-overlapping by action measure/dont_appraise, same func"
+rule="measure func=FILE_CHECK"
+ima_policy="dont_appraise func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by action audit/dont_appraise, same func"
+rule="audit func=FILE_CHECK"
+ima_policy="dont_appraise func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by action appraise/dont_measure, same func"
+rule="appraise func=FILE_CHECK"
+ima_policy="dont_measure func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by action dont_measure/hash, same func"
+rule="dont_measure func=FILE_CHECK"
+ima_policy="hash func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by uid, func is equal"
+rule="measure func=FILE_CHECK uid=0"
+ima_policy="measure uid=1 func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by uid, func is equal, same policy options"
+rule="measure func=FILE_CHECK uid=0 permit_directio"
+ima_policy="measure uid=1 func=FILE_CHECK permit_directio"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by mask, func and uid are equal, same policy options"
+rule="measure func=FILE_CHECK uid=0 permit_directio mask=MAY_READ"
+ima_policy="measure uid=0 mask=MAY_EXEC func=FILE_CHECK permit_directio"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="Non-overlapping by mask, func and uid are equal, different policy options"
+rule="measure func=FILE_CHECK uid=0 permit_directio mask=MAY_READ"
+ima_policy="measure uid=0 mask=MAY_EXEC func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+# Overlapping and different rules.
+desc="same actions, different keywords"
+rule="appraise func=FILE_CHECK"
+ima_policy="appraise uid=0"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="unrelated actions with appraise and a do action, same func"
+rule="appraise func=FILE_CHECK"
+ima_policy="measure func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="unrelated actions with appraise and a do action, different func"
+rule="appraise func=FILE_CHECK"
+ima_policy="measure func=MMAP_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="related actions, same func"
+rule="measure func=FILE_CHECK"
+ima_policy="dont_measure func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="related actions, same func, different policy options"
+rule="measure func=FILE_CHECK"
+ima_policy="dont_measure func=FILE_CHECK permit_directio"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="related actions, same func, different policy options"
+rule="measure func=FILE_CHECK permit_directio"
+ima_policy="dont_measure func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, same func, same mask with different modifier (no disjoint sets with the ^ modifier)"
+rule="measure func=FILE_CHECK mask=MAY_EXEC"
+ima_policy="measure func=FILE_CHECK mask=^MAY_EXEC"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, same func, different mask with same modifier (no disjoint sets with the ^ modifier)"
+rule="measure func=FILE_CHECK mask=^MAY_READ"
+ima_policy="measure func=FILE_CHECK mask=^MAY_EXEC"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, same func, different policy options"
+rule="measure func=FILE_CHECK"
+ima_policy="measure func=FILE_CHECK permit_directio"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, same func, different policy options"
+rule="measure func=FILE_CHECK permit_directio"
+ima_policy="measure func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, MMAP_CHECK and MMAP_CHECK_REQPROT hooks"
+rule="measure func=MMAP_CHECK"
+ima_policy="measure func=MMAP_CHECK_REQPROT"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="related actions, same func, same mask with same modifier"
+rule="measure func=FILE_CHECK mask=^MAY_EXEC"
+ima_policy="dont_measure func=FILE_CHECK mask=^MAY_EXEC"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, same func, different uid with same operator (overlap because operators are not supported)"
+rule="measure func=FILE_CHECK uid>0"
+ima_policy="measure func=FILE_CHECK uid>1"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+desc="same actions, same func, same uid with different operator (overlap because operators are not supported)"
+rule="measure func=FILE_CHECK uid>1"
+ima_policy="measure func=FILE_CHECK uid<1"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 2
+
+# Overlapping and same rules.
+desc="same actions, same func"
+rule="appraise func=FILE_CHECK"
+ima_policy="appraise func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func, same mask"
+rule="appraise mask=MAY_READ func=FILE_CHECK"
+ima_policy="appraise func=FILE_CHECK mask=MAY_READ"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func, same mask, same policy options"
+rule="appraise mask=MAY_READ func=FILE_CHECK permit_directio appraise_type=imasig"
+ima_policy="appraise func=FILE_CHECK mask=MAY_READ permit_directio appraise_type=imasig"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func"
+rule="measure func=MMAP_CHECK_REQPROT"
+ima_policy="measure func=MMAP_CHECK_REQPROT"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func with alias (PATH_CHECK = FILE_CHECK)"
+rule="measure func=FILE_CHECK"
+ima_policy="measure func=PATH_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func with alias (PATH_CHECK = FILE_CHECK), same mask with same modifiers"
+rule="measure mask=^MAY_READ func=FILE_CHECK"
+ima_policy="measure func=PATH_CHECK mask=^MAY_READ"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func with alias (PATH_CHECK = FILE_CHECK) and same mask with same modifiers, same uid with same operators"
+rule="measure mask=^MAY_READ uid>0 func=FILE_CHECK"
+ima_policy="measure func=PATH_CHECK mask=^MAY_READ uid>0"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+desc="same actions, same func with alias (PATH_CHECK = FILE_CHECK) and same mask with same modifiers, same uid with same operators"
+rule="measure mask=^MAY_READ uid<1 func=FILE_CHECK"
+ima_policy="measure func=PATH_CHECK mask=^MAY_READ uid<1"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4
+
+# Overlapping and two rules (one same, one different).
+desc="first: same actions, same func, second: unrelated actions with appraise and a do action"
+rule="appraise func=FILE_CHECK"
+ima_policy="appraise func=FILE_CHECK\nmeasure func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 6
+
+desc="first: unrelated actions with appraise and a do action, same func, second: same actions"
+rule="appraise func=FILE_CHECK"
+ima_policy="measure func=FILE_CHECK\nappraise func=FILE_CHECK"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 6
+
+desc="first: same actions, same func, same mask, second: different policy options"
+rule="appraise mask=MAY_READ func=FILE_CHECK"
+ima_policy="appraise func=FILE_CHECK mask=MAY_READ\nappraise func=FILE_CHECK mask=MAY_READ permit_directio"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 6
+
+desc="first: same actions, same func with alias (PATH_CHECK = FILE_CHECK), same mask, second: different policy options"
+rule="appraise mask=MAY_READ func=FILE_CHECK"
+ima_policy="appraise func=PATH_CHECK mask=MAY_READ\nappraise func=FILE_CHECK mask=MAY_READ permit_directio"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 6
+
+# Non-overlapping and three rules.
+desc="same actions, same func and mask, different uid"
+rule="appraise mask=MAY_READ func=FILE_CHECK uid=0"
+ima_policy="appraise mask=MAY_READ func=FILE_CHECK uid=1\nappraise mask=MAY_READ func=FILE_CHECK uid=2\nappraise mask=MAY_READ func=FILE_CHECK uid=3"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 0
+
+desc="same actions, same func and mask, different uid, except one that is the same"
+rule="appraise mask=MAY_READ func=FILE_CHECK uid=0"
+ima_policy="appraise mask=MAY_READ func=FILE_CHECK uid=1\nappraise mask=MAY_READ func=FILE_CHECK uid=0\nappraise mask=MAY_READ func=FILE_CHECK uid=3"
+expect_pass check_result "$desc" "$rule" "$ima_policy" 4