ipe: add permissive toggle

IPE, like SELinux, supports a permissive mode. This mode allows policy
authors to test and evaluate IPE policy without it affecting their
programs. When the mode is changed, a 1404 AUDIT_MAC_STATUS will
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>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/ipe/audit.c

@@ -97,8 +97,8 @@ 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));
 
@@ -225,3 +225,26 @@ 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(audit_context(), GFP_KERNEL, AUDIT_MAC_STATUS,
+		  "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);
+}

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 */

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)
 
@@ -108,6 +109,7 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
 	enum ipe_action_type action;
 	enum ipe_match match_type;
 	bool match = false;
+	int rc = 0;
 
 	rcu_read_lock();
 
@@ -159,9 +161,12 @@ int ipe_evaluate_event(const struct ipe_eval_ctx *const ctx)
 	rcu_read_unlock();
 
 	if (action == IPE_ACTION_DENY)
-		return -EACCES;
+		rc = -EACCES;
 
-	return 0;
+	if (!READ_ONCE(enforce))
+		rc = 0;
+
+	return rc;
 }
 
 /* Set the right module name */
@@ -172,3 +177,5 @@ 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");

security/ipe/eval.h

@@ -16,6 +16,7 @@
 
 extern struct ipe_policy __rcu *ipe_active_policy;
 extern bool success_audit;
+extern bool enforce;
 
 struct ipe_superblock {
 	bool initramfs;

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"
@@ -65,6 +66,58 @@ 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:
+ * * Length of buffer written	- Success
+ * * %-EPERM			- Insufficient permission
+ */
+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: Length of buffer written
+ */
+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.
@@ -123,6 +176,11 @@ 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.
  *
@@ -149,6 +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);
@@ -165,6 +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;