landlock: Add API support and docs for the quiet flags

Adds the UAPI for the quiet flags feature (but not the implementation
yet).

Even though currently LANDLOCK_ADD_RULE_QUIET only affects audit
logging, in the future this can also be used as part of a supervisor
mechanism, where it will also suppress denial notifications on a
per-object basis.  Thus the name is deliberately generic, as opposed to
e.g. LANDLOCK_ADD_RULE_LOG_QUIET.

According to pahole, even after adding the struct access_masks
quiet_masks in struct landlock_hierarchy, the u32 log_* bitfield still
only has a size of 2 bytes, so there's minimal wasted space.

Assisted-by: GitHub-Copilot:claude-opus-4.8
Signed-off-by: Tingmao Wang <m@maowtm.org>
[mic: Update date, fix comment formatting]
Link: https://patch.msgid.link/031184748a8e74c0bb02f1fa13d7a3f10918c627.1781228815.git.m@maowtm.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>

8 files changed, 89 insertions, 27 deletions

diff --git a/security/landlock/domain.h b/security/landlock/domain.h
index af100a8cd939..9f560f3c3bd1 100644
--- a/security/landlock/domain.h
+++ b/security/landlock/domain.h
@@ -111,6 +111,11 @@ struct landlock_hierarchy {
 		 * %LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON.  Set to false by default.
 		 */
 		log_new_exec : 1;
+	/**
+	 * @quiet_masks: Bitmasks of access that should be quieted (i.e. not
+	 * logged) if the related object is marked as quiet.
+	 */
+	struct access_masks quiet_masks;
 #endif /* CONFIG_AUDIT */
 };
 
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index d7cd2d5c9057..bd68a752abbf 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -325,7 +325,7 @@ retry:
  */
 int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
 			    const struct path *const path,
-			    access_mask_t access_rights)
+			    access_mask_t access_rights, const u32 flags)
 {
 	int err;
 	struct landlock_id id = {
@@ -346,7 +346,7 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
 	if (IS_ERR(id.key.object))
 		return PTR_ERR(id.key.object);
 	mutex_lock(&ruleset->lock);
-	err = landlock_insert_rule(ruleset, id, access_rights);
+	err = landlock_insert_rule(ruleset, id, access_rights, flags);
 	mutex_unlock(&ruleset->lock);
 	/*
 	 * No need to check for an error because landlock_insert_rule()
diff --git a/security/landlock/fs.h b/security/landlock/fs.h
index 911b83669e20..e4c530511360 100644
--- a/security/landlock/fs.h
+++ b/security/landlock/fs.h
@@ -136,6 +136,6 @@ __init void landlock_add_fs_hooks(void);
 
 int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
 			    const struct path *const path,
-			    access_mask_t access_hierarchy);
+			    access_mask_t access_hierarchy, const u32 flags);
 
 #endif /* _SECURITY_LANDLOCK_FS_H */
diff --git a/security/landlock/net.c b/security/landlock/net.c
index d7a4d116f7ee..cbff59ec3aba 100644
--- a/security/landlock/net.c
+++ b/security/landlock/net.c
@@ -20,7 +20,8 @@
 #include "ruleset.h"
 
 int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
-			     const u16 port, access_mask_t access_rights)
+			     const u16 port, access_mask_t access_rights,
+			     const u32 flags)
 {
 	int err;
 	const struct landlock_id id = {
@@ -35,7 +36,7 @@ int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
 			 ~landlock_get_net_access_mask(ruleset, 0);
 
 	mutex_lock(&ruleset->lock);
-	err = landlock_insert_rule(ruleset, id, access_rights);
+	err = landlock_insert_rule(ruleset, id, access_rights, flags);
 	mutex_unlock(&ruleset->lock);
 
 	return err;
diff --git a/security/landlock/net.h b/security/landlock/net.h
index 09960c237a13..5c0e3b4090cb 100644
--- a/security/landlock/net.h
+++ b/security/landlock/net.h
@@ -16,7 +16,8 @@
 __init void landlock_add_net_hooks(void);
 
 int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
-			     const u16 port, access_mask_t access_rights);
+			     const u16 port, access_mask_t access_rights,
+			     const u32 flags);
 #else /* IS_ENABLED(CONFIG_INET) */
 static inline void landlock_add_net_hooks(void)
 {
@@ -24,7 +25,7 @@ static inline void landlock_add_net_hooks(void)
 
 static inline int
 landlock_append_net_rule(struct landlock_ruleset *const ruleset, const u16 port,
-			 access_mask_t access_rights)
+			 access_mask_t access_rights, const u32 flags)
 {
 	return -EAFNOSUPPORT;
 }
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 23779e473563..4dd09ea22c84 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -21,6 +21,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/workqueue.h>
+#include <uapi/linux/landlock.h>
 
 #include "access.h"
 #include "domain.h"
@@ -255,6 +256,7 @@ static int insert_rule(struct landlock_ruleset *const ruleset,
 			if (WARN_ON_ONCE(this->layers[0].level != 0))
 				return -EINVAL;
 			this->layers[0].access |= (*layers)[0].access;
+			this->layers[0].flags.quiet |= (*layers)[0].flags.quiet;
 			return 0;
 		}
 
@@ -305,12 +307,15 @@ static void build_check_layer(void)
 /* @ruleset must be locked by the caller. */
 int landlock_insert_rule(struct landlock_ruleset *const ruleset,
 			 const struct landlock_id id,
-			 const access_mask_t access)
+			 const access_mask_t access, const u32 flags)
 {
 	struct landlock_layer layers[] = { {
 		.access = access,
 		/* When @level is zero, insert_rule() extends @ruleset. */
 		.level = 0,
+		.flags = {
+			.quiet = !!(flags & LANDLOCK_ADD_RULE_QUIET),
+		},
 	} };
 
 	build_check_layer();
@@ -351,6 +356,7 @@ static int merge_tree(struct landlock_ruleset *const dst,
 			return -EINVAL;
 
 		layers[0].access = walker_rule->layers[0].access;
+		layers[0].flags = walker_rule->layers[0].flags;
 
 		err = insert_rule(dst, id, &layers, ARRAY_SIZE(layers));
 		if (err)
@@ -581,6 +587,10 @@ landlock_merge_ruleset(struct landlock_ruleset *const parent,
 	if (err)
 		return ERR_PTR(err);
 
+#ifdef CONFIG_AUDIT
+	new_dom->hierarchy->quiet_masks = ruleset->quiet_masks;
+#endif /* CONFIG_AUDIT */
+
 	return no_free_ptr(new_dom);
 }
 
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index ffcb29a1c437..61f3c253d5c9 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -156,8 +156,8 @@ struct landlock_ruleset {
 		 * @work_free: Enables to free a ruleset within a lockless
 		 * section.  This is only used by
 		 * landlock_put_ruleset_deferred() when @usage reaches zero.
-		 * The fields @lock, @usage, @num_rules, @num_layers and
-		 * @access_masks are then unused.
+		 * The fields @lock, @usage, @num_rules, @num_layers,
+		 * @quiet_masks and @access_masks are then unused.
 		 */
 		struct work_struct work_free;
 		struct {
@@ -184,6 +184,12 @@ struct landlock_ruleset {
 			 */
 			u32 num_layers;
 			/**
+			 * @quiet_masks: Stores the quiet flags for an unmerged
+			 * ruleset.  For a merged domain, this is stored in each
+			 * layer's struct landlock_hierarchy instead.
+			 */
+			struct access_masks quiet_masks;
+			/**
 			 * @access_masks: Contains the subset of filesystem and
 			 * network actions that are restricted by a ruleset.
 			 * A domain saves all layers of merged rulesets in a
@@ -213,7 +219,7 @@ DEFINE_FREE(landlock_put_ruleset, struct landlock_ruleset *,
 
 int landlock_insert_rule(struct landlock_ruleset *const ruleset,
 			 const struct landlock_id id,
-			 const access_mask_t access);
+			 const access_mask_t access, const u32 flags);
 
 struct landlock_ruleset *
 landlock_merge_ruleset(struct landlock_ruleset *const parent,
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index d45469d5d464..36b02892c62f 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -105,8 +105,11 @@ static void build_check_abi(void)
 	ruleset_size = sizeof(ruleset_attr.handled_access_fs);
 	ruleset_size += sizeof(ruleset_attr.handled_access_net);
 	ruleset_size += sizeof(ruleset_attr.scoped);
+	ruleset_size += sizeof(ruleset_attr.quiet_access_fs);
+	ruleset_size += sizeof(ruleset_attr.quiet_access_net);
+	ruleset_size += sizeof(ruleset_attr.quiet_scoped);
 	BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size);
-	BUILD_BUG_ON(sizeof(ruleset_attr) != 24);
+	BUILD_BUG_ON(sizeof(ruleset_attr) != 48);
 
 	path_beneath_size = sizeof(path_beneath_attr.allowed_access);
 	path_beneath_size += sizeof(path_beneath_attr.parent_fd);
@@ -193,6 +196,9 @@ const int landlock_abi_version = 10;
  * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
  * - %EINVAL: unknown @flags, or unknown access, or unknown scope, or too small
  *   @size;
+ * - %EINVAL: quiet_access_fs, quiet_access_net, or quiet_scoped is not a
+ *   subset of the corresponding handled_access_fs, handled_access_net, or
+ *   scoped;
  * - %E2BIG: @attr or @size inconsistencies;
  * - %EFAULT: @attr or @size inconsistencies;
  * - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
@@ -249,6 +255,21 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
 	if ((ruleset_attr.scoped | LANDLOCK_MASK_SCOPE) != LANDLOCK_MASK_SCOPE)
 		return -EINVAL;
 
+	/*
+	 * Check that quiet masks are subsets of the respective handled masks.
+	 * Because of the checks above this is sufficient to also ensure that
+	 * the quiet masks are valid access masks.
+	 */
+	if ((ruleset_attr.quiet_access_fs | ruleset_attr.handled_access_fs) !=
+	    ruleset_attr.handled_access_fs)
+		return -EINVAL;
+	if ((ruleset_attr.quiet_access_net | ruleset_attr.handled_access_net) !=
+	    ruleset_attr.handled_access_net)
+		return -EINVAL;
+	if ((ruleset_attr.quiet_scoped | ruleset_attr.scoped) !=
+	    ruleset_attr.scoped)
+		return -EINVAL;
+
 	/* Checks arguments and transforms to kernel struct. */
 	ruleset = landlock_create_ruleset(ruleset_attr.handled_access_fs,
 					  ruleset_attr.handled_access_net,
@@ -256,6 +277,10 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
 	if (IS_ERR(ruleset))
 		return PTR_ERR(ruleset);
 
+	ruleset->quiet_masks.fs = ruleset_attr.quiet_access_fs;
+	ruleset->quiet_masks.net = ruleset_attr.quiet_access_net;
+	ruleset->quiet_masks.scope = ruleset_attr.quiet_scoped;
+
 	/* Creates anonymous FD referring to the ruleset. */
 	ruleset_fd = anon_inode_getfd("[landlock-ruleset]", &ruleset_fops,
 				      ruleset, O_RDWR | O_CLOEXEC);
@@ -320,7 +345,7 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
 }
 
 static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
-				 const void __user *const rule_attr)
+				 const void __user *const rule_attr, u32 flags)
 {
 	struct landlock_path_beneath_attr path_beneath_attr;
 	struct path path;
@@ -335,9 +360,10 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
 
 	/*
 	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
-	 * are ignored in path walks.
+	 * are ignored in path walks.  However, the rule is not useless if it is
+	 * there to hold a quiet flag.
 	 */
-	if (!path_beneath_attr.allowed_access)
+	if (!flags && !path_beneath_attr.allowed_access)
 		return -ENOMSG;
 
 	/* Checks that allowed_access matches the @ruleset constraints. */
@@ -345,6 +371,10 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
 	if ((path_beneath_attr.allowed_access | mask) != mask)
 		return -EINVAL;
 
+	/* Checks for useless quiet flag. */
+	if (flags & LANDLOCK_ADD_RULE_QUIET && !ruleset->quiet_masks.fs)
+		return -EINVAL;
+
 	/* Gets and checks the new rule. */
 	err = get_path_from_fd(path_beneath_attr.parent_fd, &path);
 	if (err)
@@ -352,13 +382,13 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
 
 	/* Imports the new rule. */
 	err = landlock_append_fs_rule(ruleset, &path,
-				      path_beneath_attr.allowed_access);
+				      path_beneath_attr.allowed_access, flags);
 	path_put(&path);
 	return err;
 }
 
 static int add_rule_net_port(struct landlock_ruleset *ruleset,
-			     const void __user *const rule_attr)
+			     const void __user *const rule_attr, u32 flags)
 {
 	struct landlock_net_port_attr net_port_attr;
 	int res;
@@ -371,9 +401,10 @@ static int add_rule_net_port(struct landlock_ruleset *ruleset,
 
 	/*
 	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
-	 * are ignored by network actions.
+	 * are ignored by network actions.  However, the rule is not useless if
+	 * it is there to hold a quiet flag.
 	 */
-	if (!net_port_attr.allowed_access)
+	if (!flags && !net_port_attr.allowed_access)
 		return -ENOMSG;
 
 	/* Checks that allowed_access matches the @ruleset constraints. */
@@ -381,13 +412,17 @@ static int add_rule_net_port(struct landlock_ruleset *ruleset,
 	if ((net_port_attr.allowed_access | mask) != mask)
 		return -EINVAL;
 
+	/* Checks for useless quiet flag. */
+	if (flags & LANDLOCK_ADD_RULE_QUIET && !ruleset->quiet_masks.net)
+		return -EINVAL;
+
 	/* Denies inserting a rule with port greater than 65535. */
 	if (net_port_attr.port > U16_MAX)
 		return -EINVAL;
 
 	/* Imports the new rule. */
 	return landlock_append_net_rule(ruleset, net_port_attr.port,
-					net_port_attr.allowed_access);
+					net_port_attr.allowed_access, flags);
 }
 
 /**
@@ -398,7 +433,7 @@ static int add_rule_net_port(struct landlock_ruleset *ruleset,
  * @rule_type: Identify the structure type pointed to by @rule_attr:
  *             %LANDLOCK_RULE_PATH_BENEATH or %LANDLOCK_RULE_NET_PORT.
  * @rule_attr: Pointer to a rule (matching the @rule_type).
- * @flags: Must be 0.
+ * @flags: Must be 0 or %LANDLOCK_ADD_RULE_QUIET.
  *
  * This system call enables to define a new rule and add it to an existing
  * ruleset.
@@ -408,20 +443,25 @@ static int add_rule_net_port(struct landlock_ruleset *ruleset,
  * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
  * - %EAFNOSUPPORT: @rule_type is %LANDLOCK_RULE_NET_PORT but TCP/IP is not
  *   supported by the running kernel;
- * - %EINVAL: @flags is not 0;
+ * - %EINVAL: @flags is not valid;
  * - %EINVAL: The rule accesses are inconsistent (i.e.
  *   &landlock_path_beneath_attr.allowed_access or
  *   &landlock_net_port_attr.allowed_access is not a subset of the ruleset
  *   handled accesses)
  * - %EINVAL: &landlock_net_port_attr.port is greater than 65535;
+ * - %EINVAL: LANDLOCK_ADD_RULE_QUIET is passed but the ruleset has no
+ *   quiet access bits set for the corresponding rule type.
  * - %ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access is
- *   0);
+ *   0) and no flags;
  * - %EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
  *   member of @rule_attr is not a file descriptor as expected;
  * - %EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
  *   @rule_attr is not the expected file descriptor type;
  * - %EPERM: @ruleset_fd has no write access to the underlying ruleset;
  * - %EFAULT: @rule_attr was not a valid address.
+ *
+ * .. kernel-doc:: include/uapi/linux/landlock.h
+ *     :identifiers: landlock_add_rule_flags
  */
 SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 		const enum landlock_rule_type, rule_type,
@@ -432,8 +472,7 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 	if (!is_initialized())
 		return -EOPNOTSUPP;
 
-	/* No flag for now. */
-	if (flags)
+	if (flags && flags != LANDLOCK_ADD_RULE_QUIET)
 		return -EINVAL;
 
 	/* Gets and checks the ruleset. */
@@ -443,9 +482,9 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 
 	switch (rule_type) {
 	case LANDLOCK_RULE_PATH_BENEATH:
-		return add_rule_path_beneath(ruleset, rule_attr);
+		return add_rule_path_beneath(ruleset, rule_attr, flags);
 	case LANDLOCK_RULE_NET_PORT:
-		return add_rule_net_port(ruleset, rule_attr);
+		return add_rule_net_port(ruleset, rule_attr, flags);
 	default:
 		return -EINVAL;
 	}