Re: [PATCH RFC v11 3/19] ipe: add evaluation loop

[Paul Moore <paul@paul-moore.com>]

On Oct  4, 2023 Fan Wu <wufan@linux.microsoft.com> wrote:
> 
> IPE must have a centralized function to evaluate incoming callers
> against IPE's policy. This iteration of the policy for against the rules
> for that specific caller is known as the evaluation loop.
> 
> Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
> ---
> v2:
> + Split evaluation loop, access control hooks, and evaluation loop from policy parser and userspace interface to pass mailing list character limit
> 
> v3:
> + Move ipe_load_properties to patch 04.
> + Remove useless 0-initializations Prefix extern variables with ipe_
> + Remove kernel module parameters, as these are exposed through sysctls.
> + Add more prose to the IPE base config option help text.
> + Use GFP_KERNEL for audit_log_start.
> + Remove unnecessary caching system.
> + Remove comments from headers
> + Use rcu_access_pointer for rcu-pointer null check
> + Remove usage of reqprot; use prot only.
> +Move policy load and activation audit event to 03/12
> 
> v4:
> + Remove sysctls in favor of securityfs nodes
> + Re-add kernel module parameters, as these are now exposed through securityfs.
> + Refactor property audit loop to a separate function.
> 
> v5:
> + fix minor grammatical errors
> + do not group rule by curly-brace in audit record,
> + reconstruct the exact rule.
> 
> v6:
> + No changes
> 
> v7:
> + Further split lsm creation into a separate commit from the evaluation loop and audit system, for easier review.
> + Propagating changes to support the new ipe_context structure in the evaluation loop.
> 
> v8:
> + Remove ipe_hook enumeration; hooks can be correlated via syscall record.
> 
> v9:
> + Remove ipe_context related code and simplify the evaluation loop.
> 
> v10:
> + Split eval part and boot_verified part
> 
> v11:
> + Fix code style issues
> ---
>  security/ipe/Makefile |  1 +
>  security/ipe/eval.c   | 96 +++++++++++++++++++++++++++++++++++++++++++
>  security/ipe/eval.h   | 24 +++++++++++
>  3 files changed, 121 insertions(+)
>  create mode 100644 security/ipe/eval.c
>  create mode 100644 security/ipe/eval.h

...

> diff --git a/security/ipe/eval.c b/security/ipe/eval.c
> new file mode 100644
> index 000000000000..5533c359bbeb
> --- /dev/null
> +++ b/security/ipe/eval.c
> @@ -0,0 +1,96 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) Microsoft Corporation. All rights reserved.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/types.h>
> +#include <linux/slab.h>
> +#include <linux/file.h>
> +#include <linux/sched.h>
> +#include <linux/rcupdate.h>
> +
> +#include "ipe.h"
> +#include "eval.h"
> +#include "policy.h"
> +
> +struct ipe_policy __rcu *ipe_active_policy;
> +
> +/**
> + * evaluate_property - Analyze @ctx against a property.
> + * @ctx: Supplies a pointer to the context to be evaluated.
> + * @p: Supplies a pointer to the property to be evaluated.
> + *
> + * Return:
> + * * true	- The current @ctx match the @p
> + * * false	- The current @ctx doesn't match the @p
> + */
> +static bool evaluate_property(const struct ipe_eval_ctx *const ctx,
> +			      struct ipe_prop *p)
> +{
> +	return false;
> +}
> +
> +/**
> + * ipe_evaluate_event - Analyze @ctx against the current active policy.
> + * @ctx: Supplies a pointer to the context to be evaluated.
> + *
> + * This is the loop where all policy evaluation happens against IPE policy.
> + *
> + * Return:
> + * * 0		- OK
> + * * -EACCES	- @ctx did not pass evaluation.
> + * * !0		- Error
> + */
> +int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
> +{
> +	bool match = false;
> +	enum ipe_action_type action;
> +	struct ipe_policy *pol = NULL;
> +	const struct ipe_rule *rule = NULL;
> +	const struct ipe_op_table *rules = NULL;
> +	struct ipe_prop *prop = NULL;
> +
> +	rcu_read_lock();
> +
> +	pol = rcu_dereference(ipe_active_policy);
> +	if (!pol) {
> +		rcu_read_unlock();
> +		return 0;
> +	}
> +
> +	if (ctx->op == IPE_OP_INVALID) {
> +		rcu_read_unlock();
> +		if (pol->parsed->global_default_action == IPE_ACTION_DENY)
> +			return -EACCES;

Assuming that the RCU lock protects @pol, shouldn't it be held until
after the global_default_action comparison?

> +		return 0;
> +	}
> +
> +	rules = &pol->parsed->rules[ctx->op];
> +
> +	list_for_each_entry(rule, &rules->rules, next) {
> +		match = true;
> +
> +		list_for_each_entry(prop, &rule->props, next) {
> +			match = match && evaluate_property(ctx, prop);

The @match variable will always be true on the right side above, or am
I missing something?

> +			if (!match)
> +				break;
> +		}
> +
> +		if (match)
> +			break;
> +	}
> +
> +	if (match)
> +		action = rule->action;
> +	else if (rules->default_action != IPE_ACTION_INVALID)
> +		action = rules->default_action;
> +	else
> +		action = pol->parsed->global_default_action;
> +
> +	rcu_read_unlock();
> +	if (action == IPE_ACTION_DENY)
> +		return -EACCES;
> +
> +	return 0;
> +}

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