[RFC PATCH 07/10] landlock: Add the new domain to landlock_cred_security

[Tingmao Wang]

We add a new field domain2 that will eventually replace the old struct
landlock_ruleset domain.  Also add get/put to appropriate places where
this struct is copied/freed.

In a future patch, this domain2 will be renamed to domain.

Signed-off-by: Tingmao Wang <m at maowtm.org>
---
 security/landlock/cred.c   |  8 ++++----
 security/landlock/cred.h   |  1 +
 security/landlock/domain.c | 17 +++++++++++++++++
 security/landlock/domain.h | 32 +++++++++++++++++++++++---------
 security/landlock/fs.c     |  5 +++++
 5 files changed, 50 insertions(+), 13 deletions(-)

diff --git a/security/landlock/cred.c b/security/landlock/cred.c
index 0cb3edde4d18..e08c9e206350 100644
--- a/security/landlock/cred.c
+++ b/security/landlock/cred.c
@@ -13,6 +13,7 @@
 
 #include "common.h"
 #include "cred.h"
+#include "domain.h"
 #include "ruleset.h"
 #include "setup.h"
 
@@ -24,6 +25,7 @@ static void hook_cred_transfer(struct cred *const new,
 
 	if (old_llcred->domain) {
 		landlock_get_ruleset(old_llcred->domain);
+		landlock_get_domain(old_llcred->domain2);
 		*landlock_cred(new) = *old_llcred;
 	}
 }
@@ -37,10 +39,8 @@ static int hook_cred_prepare(struct cred *const new,
 
 static void hook_cred_free(struct cred *const cred)
 {
-	struct landlock_ruleset *const dom = landlock_cred(cred)->domain;
-
-	if (dom)
-		landlock_put_ruleset_deferred(dom);
+	landlock_put_ruleset_deferred(landlock_cred(cred)->domain);
+	landlock_put_domain_deferred(landlock_cred(cred)->domain2);
 }
 
 #ifdef CONFIG_AUDIT
diff --git a/security/landlock/cred.h b/security/landlock/cred.h
index c82fe63ec598..b13b4c2e21aa 100644
--- a/security/landlock/cred.h
+++ b/security/landlock/cred.h
@@ -32,6 +32,7 @@ struct landlock_cred_security {
 	 * @domain: Immutable ruleset enforced on a task.
 	 */
 	struct landlock_ruleset *domain;
+	struct landlock_domain *domain2;
 
 #ifdef CONFIG_AUDIT
 	/**
diff --git a/security/landlock/domain.c b/security/landlock/domain.c
index 180ed75da9e2..321c52b275fc 100644
--- a/security/landlock/domain.c
+++ b/security/landlock/domain.c
@@ -60,6 +60,23 @@ void landlock_put_domain(struct landlock_domain *const domain)
 	}
 }
 
+static void free_domain_work(struct work_struct *const work)
+{
+	struct landlock_domain *domain;
+
+	domain = container_of(work, struct landlock_domain, work_free);
+	free_domain(domain);
+}
+
+/* Only called by hook_cred_free(). */
+void landlock_put_domain_deferred(struct landlock_domain *const domain)
+{
+	if (domain && refcount_dec_and_test(&domain->usage)) {
+		INIT_WORK(&domain->work_free, free_domain_work);
+		schedule_work(&domain->work_free);
+	}
+}
+
 #ifdef CONFIG_AUDIT
 
 /**
diff --git a/security/landlock/domain.h b/security/landlock/domain.h
index ed685f8ad52e..944420231040 100644
--- a/security/landlock/domain.h
+++ b/security/landlock/domain.h
@@ -18,6 +18,7 @@
 #include <linux/refcount.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/workqueue.h>
 
 #include "access.h"
 #include "audit.h"
@@ -26,15 +27,26 @@
 struct landlock_domain {
 	struct landlock_hashtable inode_table;
 
-	/**
-	 * @usage: Reference count for this struct.
-	 */
-	refcount_t usage;
-
-	/**
-	 * @num_layers: Number of layers in this domain.
-	 */
-	u16 num_layers;
+	union {
+		/**
+		 * @work_free: Enables to free a ruleset within a lockless
+		 * section.  This is only used by
+		 * landlock_put_domain_deferred() when @usage reaches zero.
+		 */
+		struct work_struct work_free;
+
+		struct {
+			/**
+			* @usage: Reference count for this struct.
+			*/
+			refcount_t usage;
+
+			/**
+			* @num_layers: Number of layers in this domain.
+			*/
+			u16 num_layers;
+		};
+	};
 };
 
 struct landlock_domain *landlock_alloc_domain(size_t num_inode_entries,
@@ -48,6 +60,8 @@ static inline void landlock_get_domain(struct landlock_domain *const domain)
 
 void landlock_put_domain(struct landlock_domain *const domain);
 
+void landlock_put_domain_deferred(struct landlock_domain *const domain);
+
 enum landlock_log_status {
 	LANDLOCK_LOG_PENDING = 0,
 	LANDLOCK_LOG_RECORDED,
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index b407c644ac65..c4f442093c6e 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1844,6 +1844,7 @@ static bool control_current_fowner(struct fown_struct *const fown)
 static void hook_file_set_fowner(struct file *file)
 {
 	struct landlock_ruleset *prev_dom;
+	struct landlock_domain *prev_dom2;
 	struct landlock_cred_security fown_subject = {};
 	size_t fown_layer = 0;
 
@@ -1856,11 +1857,13 @@ static void hook_file_set_fowner(struct file *file)
 				current_cred(), signal_scope, &fown_layer);
 		if (new_subject) {
 			landlock_get_ruleset(new_subject->domain);
+			landlock_get_domain(new_subject->domain2);
 			fown_subject = *new_subject;
 		}
 	}
 
 	prev_dom = landlock_file(file)->fown_subject.domain;
+	prev_dom2 = landlock_file(file)->fown_subject.domain2;
 	landlock_file(file)->fown_subject = fown_subject;
 #ifdef CONFIG_AUDIT
 	landlock_file(file)->fown_layer = fown_layer;
@@ -1868,11 +1871,13 @@ static void hook_file_set_fowner(struct file *file)
 
 	/* May be called in an RCU read-side critical section. */
 	landlock_put_ruleset_deferred(prev_dom);
+	landlock_put_domain_deferred(prev_dom2);
 }
 
 static void hook_file_free_security(struct file *file)
 {
 	landlock_put_ruleset_deferred(landlock_file(file)->fown_subject.domain);
+	landlock_put_domain_deferred(landlock_file(file)->fown_subject.domain2);
 }
 
 static struct security_hook_list landlock_hooks[] __ro_after_init = {
-- 
2.49.0