f2fs: fix to avoid racing on fsync_entry_slab by multi filesystem instances

As syzbot reported, there is an use-after-free issue during f2fs recovery:

Use-after-free write at 0xffff88823bc16040 (in kfence-#10):
 kmem_cache_destroy+0x1f/0x120 mm/slab_common.c:486
 f2fs_recover_fsync_data+0x75b0/0x8380 fs/f2fs/recovery.c:869
 f2fs_fill_super+0x9393/0xa420 fs/f2fs/super.c:3945
 mount_bdev+0x26c/0x3a0 fs/super.c:1367
 legacy_get_tree+0xea/0x180 fs/fs_context.c:592
 vfs_get_tree+0x86/0x270 fs/super.c:1497
 do_new_mount fs/namespace.c:2905 [inline]
 path_mount+0x196f/0x2be0 fs/namespace.c:3235
 do_mount fs/namespace.c:3248 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3433
 do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The root cause is multi f2fs filesystem instances can race on accessing
global fsync_entry_slab pointer, result in use-after-free issue of slab
cache, fixes to init/destroy this slab cache only once during module
init/destroy procedure to avoid this issue.

Reported-by: syzbot+9d90dad32dd9727ed084@syzkaller.appspotmail.com
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -3620,6 +3620,8 @@ void f2fs_destroy_garbage_collection_cache(void);
  */
 int f2fs_recover_fsync_data(struct f2fs_sb_info *sbi, bool check_only);
 bool f2fs_space_for_roll_forward(struct f2fs_sb_info *sbi);
+int __init f2fs_create_recovery_cache(void);
+void f2fs_destroy_recovery_cache(void);
 
 /*
  * debug.c

fs/f2fs/recovery.c

@@ -788,13 +788,6 @@ int f2fs_recover_fsync_data(struct f2fs_sb_info *sbi, bool check_only)
 	quota_enabled = f2fs_enable_quota_files(sbi, s_flags & SB_RDONLY);
 #endif
 
-	fsync_entry_slab = f2fs_kmem_cache_create("f2fs_fsync_inode_entry",
-			sizeof(struct fsync_inode_entry));
-	if (!fsync_entry_slab) {
-		err = -ENOMEM;
-		goto out;
-	}
-
 	INIT_LIST_HEAD(&inode_list);
 	INIT_LIST_HEAD(&tmp_inode_list);
 	INIT_LIST_HEAD(&dir_list);
@@ -867,8 +860,6 @@ int f2fs_recover_fsync_data(struct f2fs_sb_info *sbi, bool check_only)
 		}
 	}
 
-	kmem_cache_destroy(fsync_entry_slab);
-out:
 #ifdef CONFIG_QUOTA
 	/* Turn quotas off */
 	if (quota_enabled)
@@ -878,3 +869,17 @@ int f2fs_recover_fsync_data(struct f2fs_sb_info *sbi, bool check_only)
 
 	return ret ? ret : err;
 }
+
+int __init f2fs_create_recovery_cache(void)
+{
+	fsync_entry_slab = f2fs_kmem_cache_create("f2fs_fsync_inode_entry",
+					sizeof(struct fsync_inode_entry));
+	if (!fsync_entry_slab)
+		return -ENOMEM;
+	return 0;
+}
+
+void f2fs_destroy_recovery_cache(void)
+{
+	kmem_cache_destroy(fsync_entry_slab);
+}

fs/f2fs/super.c

@@ -4227,9 +4227,12 @@ static int __init init_f2fs_fs(void)
 	err = f2fs_create_checkpoint_caches();
 	if (err)
 		goto free_segment_manager_caches;
-	err = f2fs_create_extent_cache();
+	err = f2fs_create_recovery_cache();
 	if (err)
 		goto free_checkpoint_caches;
+	err = f2fs_create_extent_cache();
+	if (err)
+		goto free_recovery_cache;
 	err = f2fs_create_garbage_collection_cache();
 	if (err)
 		goto free_extent_cache;
@@ -4278,6 +4281,8 @@ static int __init init_f2fs_fs(void)
 	f2fs_destroy_garbage_collection_cache();
 free_extent_cache:
 	f2fs_destroy_extent_cache();
+free_recovery_cache:
+	f2fs_destroy_recovery_cache();
 free_checkpoint_caches:
 	f2fs_destroy_checkpoint_caches();
 free_segment_manager_caches:
@@ -4303,6 +4308,7 @@ static void __exit exit_f2fs_fs(void)
 	f2fs_exit_sysfs();
 	f2fs_destroy_garbage_collection_cache();
 	f2fs_destroy_extent_cache();
+	f2fs_destroy_recovery_cache();
 	f2fs_destroy_checkpoint_caches();
 	f2fs_destroy_segment_manager_caches();
 	f2fs_destroy_node_manager_caches();