throne_tracker: avoid cross-fs traversal using s_magic check

Skip directories that does NOT have the same magic as /data/app.
This is to avoid scanning incfs and any other stacked filesystems.

This is a workaround for Ultra-Legacy kernels where upstream's
method fails.

Replaces:
`throne_tracker: avoid cross fs access`
tiann/KernelSU#2626

Signed-off-by: backslashxx <[email protected]>

Author: backslashxx

drivers/kernelsu/throne_tracker.c

@@ -225,6 +225,7 @@ void search_manager(const char *path, int depth, struct list_head *uid_data)
 	int i, stop = 0;
 	struct list_head data_path_list;
 	INIT_LIST_HEAD(&data_path_list);
+	unsigned long data_app_magic = 0;
 
 	// Initialize APK cache list
 	struct apk_path_hash *pos, *n;
@@ -271,6 +272,22 @@ void search_manager(const char *path, int depth, struct list_head *uid_data)
 					pr_err("Failed to open directory: %s, err: %ld\n", pos->dirpath, PTR_ERR(file));
 					goto skip_iterate;
 				}
+				
+				// grab magic on first folder, which is /data/app
+				if (!data_app_magic) {
+					if (file->f_inode->i_sb->s_magic) {
+						data_app_magic = file->f_inode->i_sb->s_magic;
+						pr_info("%s: dir: %s got magic! %lx\n", __func__, pos->dirpath, data_app_magic);
+					} else
+						goto skip_iterate;
+				}
+				
+				if (file->f_inode->i_sb->s_magic != data_app_magic) {
+					pr_info("%s: skip: %s magic: %lx expected: %lx\n", __func__, pos->dirpath, 
+						file->f_inode->i_sb->s_magic, data_app_magic);
+					filp_close(file, NULL);
+					goto skip_iterate;
+				}
 
 				iterate_dir(file, &ctx.ctx);
 				filp_close(file, NULL);