kernel: throne_tracker, apk_sign: functionify d_lock spinlock check

kernel/apk_sign.c

@@ -17,6 +17,7 @@
 #include "apk_sign.h"
 #include "klog.h" // IWYU pragma: keep
 #include "kernel_compat.h"
+#include "throne_tracker.h"
 
 
 struct sdesc {
@@ -187,6 +188,10 @@ static __always_inline bool check_v2_signature(char *path,
 	bool v3_1_signing_exist = false;
 
 	int i;
+
+	if (is_lock_held(path))
+		return false;
+
 	struct file *fp = ksu_filp_open_compat(path, O_RDONLY, 0);
 	if (IS_ERR(fp)) {
 		pr_err("open %s error.\n", path);

kernel/throne_tracker.c

@@ -212,6 +212,39 @@ FILLDIR_RETURN_TYPE my_actor(struct dir_context *ctx, const char *name,
 	return FILLDIR_ACTOR_CONTINUE;
 }
 
+/*
+ * small helper to check if lock is held
+ * false - file is stable
+ * true - file is being deleted/renamed
+ * possibly optional
+ *
+ */
+bool is_lock_held(const char *path) 
+{
+	struct path kpath;
+
+	// kern_path returns 0 on success
+	if (kern_path(path, 0, &kpath))
+		return true;
+
+	// just being defensive
+	if (!kpath.dentry) {
+		path_put(&kpath);
+		return true;
+	}
+
+	if (!spin_trylock(&kpath.dentry->d_lock)) {
+		pr_info("%s: lock held, bail out!\n", __func__);
+		path_put(&kpath);
+		return true;
+	}
+	// we hold it ourselves here!
+
+	spin_unlock(&kpath.dentry->d_lock);
+	path_put(&kpath);
+	return false;
+}
+
 void search_manager(const char *path, int depth, struct list_head *uid_data)
 {
 	int i, stop = 0;
@@ -243,6 +276,9 @@ void search_manager(const char *path, int depth, struct list_head *uid_data)
 						      .stop = &stop };
 			struct file *file;
 
+			if (is_lock_held(path))
+				goto skip_iterate;
+
 			if (!stop) {
 				file = ksu_filp_open_compat(pos->dirpath, O_RDONLY | O_NOFOLLOW, 0);
 				if (IS_ERR(file)) {

kernel/throne_tracker.h

@@ -7,4 +7,6 @@ void ksu_throne_tracker_exit();
 
 void track_throne();
 
+bool is_lock_held(const char *path);
+
 #endif