[RFC PATCH v1 6/7] landlock: Log mount-related requests

["Mickaël Salaün" <mic@digikod.net>]

Add audit support for mount, move_mount, umount, remount, and pivot_root
requests.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 security/landlock/audit.c | 26 ++++++++++++-
 security/landlock/audit.h | 13 ++++++-
 security/landlock/fs.c    | 82 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 109 insertions(+), 12 deletions(-)

diff --git a/security/landlock/audit.c b/security/landlock/audit.c
index 148fc0fafef4..89bd701d124f 100644
--- a/security/landlock/audit.c
+++ b/security/landlock/audit.c
@@ -18,6 +18,11 @@ static const char *op_to_string(enum landlock_operation operation)
 {
 	const char *const desc[] = {
 		[0] = "",
+		[LANDLOCK_OP_MOUNT] = "mount",
+		[LANDLOCK_OP_MOVE_MOUNT] = "move_mount",
+		[LANDLOCK_OP_UMOUNT] = "umount",
+		[LANDLOCK_OP_REMOUNT] = "remount",
+		[LANDLOCK_OP_PIVOT_ROOT] = "pivot_root",
 		[LANDLOCK_OP_MKDIR] = "mkdir",
 		[LANDLOCK_OP_MKNOD] = "mknod",
 		[LANDLOCK_OP_SYMLINK] = "symlink",
@@ -33,6 +38,20 @@ static const char *op_to_string(enum landlock_operation operation)
 	return desc[operation];
 }
 
+static const char *perm_to_string(enum landlock_permission permission)
+{
+	const char *const desc[] = {
+		[0] = "",
+		[LANDLOCK_PERM_PTRACE] = "ptrace",
+		[LANDLOCK_PERM_FS_LAYOUT] = "fs_layout",
+	};
+
+	if (WARN_ON_ONCE(permission < 0 || permission > ARRAY_SIZE(desc)))
+		return "unknown";
+
+	return desc[permission];
+}
+
 #define BIT_INDEX(bit) HWEIGHT(bit - 1)
 
 static void log_accesses(struct audit_buffer *const ab,
@@ -177,8 +196,11 @@ update_request(struct landlock_request *const request,
 	WARN_ON_ONCE(request->youngest_domain);
 	WARN_ON_ONCE(request->missing_access);
 
-	if (WARN_ON_ONCE(!access_request))
+	if (!access_request) {
+		/* No missing accesses. */
+		request->youngest_domain = node->id;
 		return;
+	}
 
 	if (WARN_ON_ONCE(!layer_masks))
 		return;
@@ -240,6 +262,8 @@ log_request(const int error, struct landlock_request *const request,
 			 request->youngest_domain,
 			 op_to_string(request->operation), -error);
 	log_accesses(ab, request->missing_access);
+	audit_log_format(ab, " missing-permission=%s",
+			 perm_to_string(request->missing_permission));
 	audit_log_lsm_data(ab, &request->audit);
 	audit_log_end(ab);
 }
diff --git a/security/landlock/audit.h b/security/landlock/audit.h
index 8edc68b98fca..e559fb6a89dd 100644
--- a/security/landlock/audit.h
+++ b/security/landlock/audit.h
@@ -14,7 +14,12 @@
 #include "ruleset.h"
 
 enum landlock_operation {
-	LANDLOCK_OP_MKDIR = 1,
+	LANDLOCK_OP_MOUNT = 1,
+	LANDLOCK_OP_MOVE_MOUNT,
+	LANDLOCK_OP_UMOUNT,
+	LANDLOCK_OP_REMOUNT,
+	LANDLOCK_OP_PIVOT_ROOT,
+	LANDLOCK_OP_MKDIR,
 	LANDLOCK_OP_MKNOD,
 	LANDLOCK_OP_SYMLINK,
 	LANDLOCK_OP_UNLINK,
@@ -23,8 +28,14 @@ enum landlock_operation {
 	LANDLOCK_OP_OPEN,
 };
 
+enum landlock_permission {
+	LANDLOCK_PERM_PTRACE = 1,
+	LANDLOCK_PERM_FS_LAYOUT,
+};
+
 struct landlock_request {
 	const enum landlock_operation operation;
+	const enum landlock_permission missing_permission;
 	access_mask_t missing_access;
 	u64 youngest_domain;
 	struct common_audit_data audit;
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 104dfb2abc32..8600530e304c 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1050,17 +1050,41 @@ static int hook_sb_mount(const char *const dev_name,
 			 const struct path *const path, const char *const type,
 			 const unsigned long flags, void *const data)
 {
-	if (!landlock_get_current_domain())
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+	struct landlock_request request = {
+		.operation = LANDLOCK_OP_MOUNT,
+		.missing_permission = LANDLOCK_PERM_FS_LAYOUT,
+		.audit = {
+			.type = LSM_AUDIT_DATA_PATH,
+			.u.path = *path,
+		},
+	};
+
+	if (!dom)
 		return 0;
-	return -EPERM;
+
+	return landlock_log_request(-EPERM, &request, dom, 0, NULL);
 }
 
 static int hook_move_mount(const struct path *const from_path,
 			   const struct path *const to_path)
 {
-	if (!landlock_get_current_domain())
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+	struct landlock_request request = {
+		.operation = LANDLOCK_OP_MOVE_MOUNT,
+		.missing_permission = LANDLOCK_PERM_FS_LAYOUT,
+		.audit = {
+			.type = LSM_AUDIT_DATA_PATH,
+			.u.path = *to_path,
+		},
+	};
+
+	if (!dom)
 		return 0;
-	return -EPERM;
+
+	return landlock_log_request(-EPERM, &request, dom, 0, NULL);
 }
 
 /*
@@ -1069,16 +1093,42 @@ static int hook_move_mount(const struct path *const from_path,
  */
 static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
 {
-	if (!landlock_get_current_domain())
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+	struct landlock_request request = {
+		.operation = LANDLOCK_OP_UMOUNT,
+		.missing_permission = LANDLOCK_PERM_FS_LAYOUT,
+		.audit = {
+			// TODO: try to print the mounted path
+			// cf. dentry_path()
+			.type = LSM_AUDIT_DATA_DENTRY,
+			.u.dentry = mnt->mnt_root,
+		},
+	};
+
+	if (!dom)
 		return 0;
-	return -EPERM;
+
+	return landlock_log_request(-EPERM, &request, dom, 0, NULL);
 }
 
 static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
 {
-	if (!landlock_get_current_domain())
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+	struct landlock_request request = {
+		.operation = LANDLOCK_OP_REMOUNT,
+		.missing_permission = LANDLOCK_PERM_FS_LAYOUT,
+		.audit = {
+			.type = LSM_AUDIT_DATA_DENTRY,
+			.u.dentry = sb->s_root,
+		},
+	};
+
+	if (!dom)
 		return 0;
-	return -EPERM;
+
+	return landlock_log_request(-EPERM, &request, dom, 0, NULL);
 }
 
 /*
@@ -1092,9 +1142,21 @@ static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
 static int hook_sb_pivotroot(const struct path *const old_path,
 			     const struct path *const new_path)
 {
-	if (!landlock_get_current_domain())
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+	struct landlock_request request = {
+		.operation = LANDLOCK_OP_PIVOT_ROOT,
+		.missing_permission = LANDLOCK_PERM_FS_LAYOUT,
+		.audit = {
+			.type = LSM_AUDIT_DATA_PATH,
+			.u.path = *new_path,
+		},
+	};
+
+	if (!dom)
 		return 0;
-	return -EPERM;
+
+	return landlock_log_request(-EPERM, &request, dom, 0, NULL);
 }
 
 /* Path hooks */
-- 
2.42.0