[PATCH] nilfs2: fix kernel bug due to missing clearing of checked flag

[Ryusuke Konishi]

Syzbot reported that in directory operations after nilfs2 detects
filesystem corruption and degrades to read-only,
__block_write_begin_int(), which is called to prepare block writes,
may fail the BUG_ON check for accesses exceeding the folio/page size,
triggering a kernel bug.

This was found to be because the "checked" flag of a page/folio was
not cleared when it was discarded by nilfs2's own routine, which
causes the sanity check of directory entries to be skipped when the
directory page/folio is reloaded.  So, fix that.

This was necessary when the use of nilfs2's own page discard routine
was applied to more than just metadata files.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Reported-by: syzbot+d6ca2daf692c7a82f959@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=d6ca2daf692c7a82f959
Fixes: 8c26c4e2694a ("nilfs2: fix issue with flush kernel thread after remount in RO mode because of driver's internal error or metadata corruption")
Cc: stable@xxxxxxxxxxxxxxx
---
Hi Andrew, please apply this as a bug fix.

This fixes another kernel bug recently reported by syzbot.

Thanks,
Ryusuke Konishi

 fs/nilfs2/page.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
index 5436eb0424bd..10def4b55995 100644
--- a/fs/nilfs2/page.c
+++ b/fs/nilfs2/page.c
@@ -401,6 +401,7 @@ void nilfs_clear_folio_dirty(struct folio *folio)
 
 	folio_clear_uptodate(folio);
 	folio_clear_mappedtodisk(folio);
+	folio_clear_checked(folio);
 
 	head = folio_buffers(folio);
 	if (head) {
-- 
2.43.0