From ce2739e482bce8d2c014d76c4531c877f382aa54 Mon Sep 17 00:00:00 2001 From: Chao Yu Date: Wed, 7 Jan 2026 19:22:18 +0800 Subject: [PATCH] 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: e234088758fc ("f2fs: avoid wait if IO end up when do_checkpoint for better performance") Reported-by: syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187 Signed-off-by: Chao Yu Signed-off-by: Jaegeuk Kim --- fs/f2fs/data.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index 2e133a723b99..f461f1318b4c 100644 --- a/fs/f2fs/data.c +++ b/fs/f2fs/data.c @@ -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); } -- 2.47.3