[RFC PATCH v10 09/17] ipe: add permissive toggle

Fan Wu
2023-06-28T21:10:54Z

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.
---
security/ipe/audit.c | 22 ++++++++++++++
security/ipe/audit.h | 1 +
security/ipe/eval.c | 9 ++++++
security/ipe/eval.h | 1 +
security/ipe/fs.c | 69 ++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 102 insertions(+)

diff --git a/security/ipe/audit.c b/security/ipe/audit.c
index d3f78a7fc93f..08f855f70f76 100644
--- a/security/ipe/audit.c
+++ b/security/ipe/audit.c
@@ -195,3 +195,25 @@ 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, "enforcing=%d old_enforcing=%d auid=%u ses=%u"
+ " enabled=1 old-enabled=1 lsm=ipe res=1",
+ 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 2cb43ad92a65..2d4b3a6d7b7a 100644
--- a/security/ipe/eval.c
+++ b/security/ipe/eval.c
@@ -20,6 +20,7 @@

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

static const struct super_block *pinned_sb;
static DEFINE_SPINLOCK(pin_lock);
@@ -116,6 +117,7 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
{
int rc = 0;
bool match = false;
+ bool enforcing = true;
enum ipe_action_type action;
enum ipe_match match_type;
struct ipe_policy *pol = NULL;
@@ -131,6 +133,8 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
return 0;
}

+ enforcing = READ_ONCE(enforce);
+
if (ctx->op == __IPE_OP_INVALID) {
action = pol->parsed->global_default_action;
match_type = __IPE_MATCH_GLOBAL;
@@ -167,6 +171,9 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
if (action == __IPE_ACTION_DENY)
rc = -EACCES;

+ if (!enforcing)
+ rc = 0;
+
return rc;
}

@@ -196,3 +203,5 @@ void ipe_invalidate_pinned_sb(const struct super_block *mnt_sb)

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 8fcdb2ea19f4..15c35921fd4d 100644
--- a/security/ipe/eval.h
+++ b/security/ipe/eval.h
@@ -14,6 +14,7 @@

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

struct ipe_eval_ctx {
enum ipe_op_type op;
diff --git a/security/ipe/fs.c b/security/ipe/fs.c
index 6bd2aa84831b..1761d39e4d04 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"
@@ -68,6 +69,61 @@ 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);
+ new_value = old_value;
+ 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.
@@ -121,6 +177,11 @@ 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.
*
@@ -148,6 +209,13 @@ 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);
@@ -164,6 +232,7 @@ 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;
--
2.25.1