[RFC PATCH v12 10/20] ipe: add permissive toggle

Fan Wu
2024-01-30T22:37:25Z

From: Deven Bowers <deven.desai@linux.microsoft.com>

IPE, like SELinux, supports a permissive mode. This mode allows policy
authors to test and evaluate IPE policy without it effecting their
programs. When the mode is changed, a 1404 AUDIT_MAC_STATUS
be reported.

This patch adds the following audit records:

audit: MAC_STATUS enforcing=0 old_enforcing=1 auid=4294967295
ses=4294967295 enabled=1 old-enabled=1 lsm=ipe res=1
audit: MAC_STATUS enforcing=1 old_enforcing=0 auid=4294967295
ses=4294967295 enabled=1 old-enabled=1 lsm=ipe res=1

The audit record only emit when the value from the user input is
different from the current enforce value.

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.
+ Split out permissive functionality into a separate patch for easier
review.
+ Remove permissive switch compile-time configuration option - this
is trivial to add later.

v8:
+ Remove "IPE" prefix from permissive audit record
+ align fields to the linux-audit field dictionary. This causes the
following fields to change:
enforce -> permissive

+ Remove duplicated information correlated with syscall record, that
will always be present in the audit event.
+ Change audit types:
+ AUDIT_TRUST_STATUS -> AUDIT_MAC_STATUS
+ There is no significant difference in meaning between
these types.

v9:
+ Clean up ipe_context related code

v10:
+ Change audit format to comform with the existing format selinux is
using
+ Remove the audit record emission during init to align with selinux,
which does not perform this action.

v11:
+ Remove redundant code

v12:
+ Remove redundant code
---
security/ipe/audit.c | 27 ++++++++++++++++--
security/ipe/audit.h | 1 +
security/ipe/eval.c | 11 +++++--
security/ipe/eval.h | 1 +
security/ipe/fs.c | 68 ++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 104 insertions(+), 4 deletions(-)

diff --git a/security/ipe/audit.c b/security/ipe/audit.c
index 79b7af25085c..ed390d32c641 100644
--- a/security/ipe/audit.c
+++ b/security/ipe/audit.c
@@ -27,6 +27,9 @@
"new_active_pol_version=%hu.%hu.%hu "\
"new_policy_digest=" IPE_AUDIT_HASH_ALG ":"

+#define AUDIT_ENFORCE_CHANGE_FMT "enforcing=%d old_enforcing=%d auid=%u ses=%u "\
+ "enabled=1 old-enabled=1 lsm=ipe res=1"
+
static const char *const audit_op_names[__IPE_OP_MAX + 1] = {
"EXECUTE",
"FIRMWARE",
@@ -95,8 +98,8 @@ void ipe_audit_match(const struct ipe_eval_ctx *const ctx,
if (!ab)
return;

- audit_log_format(ab, "ipe_op=%s ipe_hook=%s pid=%d comm=",
- op, audit_hook_names[ctx->hook],
+ audit_log_format(ab, "ipe_op=%s ipe_hook=%s enforcing=%d pid=%d comm=",
+ op, audit_hook_names[ctx->hook], READ_ONCE(enforce),
task_tgid_nr(current));
audit_log_untrustedstring(ab, get_task_comm(comm, current));

@@ -210,3 +213,23 @@ void ipe_audit_policy_load(const struct ipe_policy *const p)

audit_log_end(ab);
}
+
+/**
+ * ipe_audit_enforce - Audit a change in IPE's enforcement state.
+ * @new_enforce: The new value enforce to be set.
+ * @old_enforce: The old value currently in enforce.
+ */
+void ipe_audit_enforce(bool new_enforce, bool old_enforce)
+{
+ struct audit_buffer *ab;
+
+ ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_MAC_STATUS);
+ if (!ab)
+ return;
+
+ audit_log_format(ab, AUDIT_ENFORCE_CHANGE_FMT, new_enforce, old_enforce,
+ from_kuid(&init_user_ns, audit_get_loginuid(current)),
+ audit_get_sessionid(current));
+
+ audit_log_end(ab);
+}
diff --git a/security/ipe/audit.h b/security/ipe/audit.h
index 0ff5a06808de..914f001e5286 100644
--- a/security/ipe/audit.h
+++ b/security/ipe/audit.h
@@ -14,5 +14,6 @@ void ipe_audit_match(const struct ipe_eval_ctx *const ctx,
void ipe_audit_policy_load(const struct ipe_policy *const p);
void ipe_audit_policy_activation(const struct ipe_policy *const op,
const struct ipe_policy *const np);
+void ipe_audit_enforce(bool new_enforce, bool old_enforce);

#endif /* _IPE_AUDIT_H */
diff --git a/security/ipe/eval.c b/security/ipe/eval.c
index 85cccc3d0bdf..49338b35f126 100644
--- a/security/ipe/eval.c
+++ b/security/ipe/eval.c
@@ -18,6 +18,7 @@

struct ipe_policy __rcu *ipe_active_policy;
bool success_audit;
+bool enforce = true;

#define FILE_SUPERBLOCK(f) ((f)->f_path.mnt->mnt_sb)

@@ -137,6 +138,7 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
const struct ipe_rule *rule = NULL;
const struct ipe_op_table *rules = NULL;
struct ipe_prop *prop = NULL;
+ int rc = 0;

rcu_read_lock();

@@ -189,9 +191,12 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
ipe_audit_match(ctx, match_type, action, rule);

if (action == IPE_ACTION_DENY)
- return -EACCES;
+ rc = -EACCES;

- return 0;
+ if (!READ_ONCE(enforce))
+ rc = 0;
+
+ return rc;
}

/* Set the right module name */
@@ -202,3 +207,5 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)

module_param(success_audit, bool, 0400);
MODULE_PARM_DESC(success_audit, "Start IPE with success auditing enabled");
+module_param(enforce, bool, 0400);
+MODULE_PARM_DESC(enforce, "Start IPE in enforce or permissive mode");
diff --git a/security/ipe/eval.h b/security/ipe/eval.h
index 0be9aadec9f8..84adf1a0e514 100644
--- a/security/ipe/eval.h
+++ b/security/ipe/eval.h
@@ -16,6 +16,7 @@

extern struct ipe_policy __rcu *ipe_active_policy;
extern bool success_audit;
+extern bool enforce;

#ifdef CONFIG_BLK_DEV_INITRD
struct ipe_sb {
diff --git a/security/ipe/fs.c b/security/ipe/fs.c
index 95407997cf0c..b16d87443a3b 100644
--- a/security/ipe/fs.c
+++ b/security/ipe/fs.c
@@ -16,6 +16,7 @@ static struct dentry *np __ro_after_init;
static struct dentry *root __ro_after_init;
struct dentry *policy_root __ro_after_init;
static struct dentry *audit_node __ro_after_init;
+static struct dentry *enforce_node __ro_after_init;

/**
* setaudit - Write handler for the securityfs node, "ipe/success_audit"
@@ -67,6 +68,60 @@ static ssize_t getaudit(struct file *f, char __user *data,
return simple_read_from_buffer(data, len, offset, result, 1);
}

+/**
+ * setenforce - Write handler for the securityfs node, "ipe/enforce"
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * >0 - Success, Length of buffer written
+ * * <0 - Error
+ */
+static ssize_t setenforce(struct file *f, const char __user *data,
+ size_t len, loff_t *offset)
+{
+ int rc = 0;
+ bool new_value, old_value;
+
+ if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+ return -EPERM;
+
+ old_value = READ_ONCE(enforce);
+ rc = kstrtobool_from_user(data, len, &new_value);
+ if (rc)
+ return rc;
+
+ if (new_value != old_value) {
+ ipe_audit_enforce(new_value, old_value);
+ WRITE_ONCE(enforce, new_value);
+ }
+
+ return len;
+}
+
+/**
+ * getenforce - Read handler for the securityfs node, "ipe/enforce"
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the read syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * >0 - Success, Length of buffer written
+ * * <0 - Error
+ */
+static ssize_t getenforce(struct file *f, char __user *data,
+ size_t len, loff_t *offset)
+{
+ const char *result;
+
+ result = ((READ_ONCE(enforce)) ? "1" : "0");
+
+ return simple_read_from_buffer(data, len, offset, result, 1);
+}
+
/**
* new_policy - Write handler for the securityfs node, "ipe/new_policy".
* @f: Supplies a file structure representing the securityfs node.
@@ -120,6 +175,11 @@ static const struct file_operations audit_fops = {
.read = getaudit,
};

+static const struct file_operations enforce_fops = {
+ .write = setenforce,
+ .read = getenforce,
+};
+
/**
* ipe_init_securityfs - Initialize IPE's securityfs tree at fsinit.
*
@@ -147,6 +207,13 @@ static int __init ipe_init_securityfs(void)
goto err;
}

+ enforce_node = securityfs_create_file("enforce", 0600, root, NULL,
+ &enforce_fops);
+ if (IS_ERR(enforce_node)) {
+ rc = PTR_ERR(enforce_node);
+ goto err;
+ }
+
policy_root = securityfs_create_dir("policies", root);
if (IS_ERR(policy_root)) {
rc = PTR_ERR(policy_root);
@@ -163,6 +230,7 @@ static int __init ipe_init_securityfs(void)
err:
securityfs_remove(np);
securityfs_remove(policy_root);
+ securityfs_remove(enforce_node);
securityfs_remove(audit_node);
securityfs_remove(root);
return rc;
--
2.43.0