fuse: limit FUSE_NOTIFY_RETRIEVE to uptodate folios

commit 4e3d1b2 upstream.

FUSE_NOTIFY_RETRIEVE must be limited to uptodate folios; !uptodate folios
can contain uninitialized data.
Since FUSE_NOTIFY_RETRIEVE is intended to only return data that is already
in the page cache and not wait for data from the FUSE daemon, treat
!uptodate folios as if they weren't present.

This only has security impact on systems that don't enable automatic
zero-initialization of all page allocations via
CONFIG_INIT_ON_ALLOC_DEFAULT_ON or init_on_alloc=1.

Cc: stable@kernel.org
Fixes: 2d45ba3 ("fuse: add retrieve request")
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://patch.msgid.link/20260519-fuse-retrieve-uptodate-v1-1-a7a1912a37f9@google.com
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: thejh

fs/fuse/dev.c

@@ -1928,6 +1928,10 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 		folio = filemap_get_folio(mapping, index);
 		if (IS_ERR(folio))
 			break;
+		if (!folio_test_uptodate(folio)) {
+			folio_put(folio);
+			break;
+		}
 
 		folio_offset = ((index - folio->index) << PAGE_SHIFT) + offset;
 		nr_bytes = min(folio_size(folio) - folio_offset, num);