On Mon, Feb 10, 2025 at 02:12:35PM -0500, Josef Bacik wrote:
> From: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Date: Mon, 10 Feb 2025 14:06:40 -0500
> Subject: [PATCH] fuse: drop extra put of folio when using pipe splice
>
> In 3eab9d7bc2f4 ("fuse: convert readahead to use folios"), I converted
> us to using the new folio readahead code, which drops the reference on
> the folio once it is locked, using an inferred reference on the folio.
> Previously we held a reference on the folio for the entire duration of
> the readpages call.
>
> This is fine, however I failed to catch the case for splice pipe
> responses where we will remove the old folio and splice in the new
> folio. Here we assumed that there is a reference held on the folio for
> ap->folios, which is no longer the case.
>
> To fix this, simply drop the extra put to keep us consistent with the
> non-splice variation. This will fix the UAF bug that was reported.
>
> Link: https://lore.kernel.org/linux-fsdevel/2f681f48-00f5-4e09-8431-2b3dbfaa881e@xxxxxxxxx/
> Fixes: 3eab9d7bc2f4 ("fuse: convert readahead to use folios")
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
> fs/fuse/dev.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 5b5f789b37eb..5bd6e2e184c0 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -918,8 +918,6 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
> }
>
> folio_unlock(oldfolio);
> - /* Drop ref for ap->pages[] array */
> - folio_put(oldfolio);
> cs->len = 0;
But aren't we now leaking a reference to newfolio? ie shouldn't
we also:
- folio_get(newfolio);
a few lines earlier?
