Commit ce2739e4 authored by Chao Yu's avatar Chao Yu Committed by Jaegeuk Kim
Browse files

f2fs: fix to avoid UAF in f2fs_write_end_io() 



As syzbot reported an use-after-free issue in f2fs_write_end_io().

It is caused by below race condition:

loop device				umount
- worker_thread
 - loop_process_work
  - do_req_filebacked
   - lo_rw_aio
    - lo_rw_aio_complete
     - blk_mq_end_request
      - blk_update_request
       - f2fs_write_end_io
        - dec_page_count
        - folio_end_writeback
					- kill_f2fs_super
					 - kill_block_super
					  - f2fs_put_super
					 : free(sbi)
       : get_pages(, F2FS_WB_CP_DATA)
         accessed sbi which is freed

In kill_f2fs_super(), we will drop all page caches of f2fs inodes before
call free(sbi), it guarantee that all folios should end its writeback, so
it should be safe to access sbi before last folio_end_writeback().

Let's relocate ckpt thread wakeup flow before folio_end_writeback() to
resolve this issue.

Cc: stable@kernel.org
Fixes: e2340887 ("f2fs: avoid wait if IO end up when do_checkpoint for better performance")
Reported-by: default avatar <syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187


Signed-off-by: default avatarChao Yu <chao@kernel.org>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
parent 3996b702

fs/f2fs/data.c

+9 −3
Original line number Diff line number Diff line
@@ -378,14 +378,20 @@ static void f2fs_write_end_io(struct bio *bio) 
				folio->index != nid_of_node(folio));



		dec_page_count(sbi, type);



		/*

		 * we should access sbi before folio_end_writeback() to

		 * avoid racing w/ kill_f2fs_super()

		 */

		if (type == F2FS_WB_CP_DATA && !get_pages(sbi, type) &&

				wq_has_sleeper(&sbi->cp_wait))

			wake_up(&sbi->cp_wait);



		if (f2fs_in_warm_node_list(sbi, folio))

			f2fs_del_fsync_node_entry(sbi, folio);

		folio_clear_f2fs_gcing(folio);

		folio_end_writeback(folio);

	}

	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&

				wq_has_sleeper(&sbi->cp_wait))

		wake_up(&sbi->cp_wait);



	bio_put(bio);

}