Re: BUG: unable to handle kernel paging request in fuse_copy_do

[Miklos Szeredi]

On Fri, 22 Mar 2024 at 22:56, David Hildenbrand <david@xxxxxxxxxx> wrote:

>  From 85558a46d9f249f26bd77dd3b18d14f248464845 Mon Sep 17 00:00:00 2001
> From: David Hildenbrand <david@xxxxxxxxxx>
> Date: Fri, 22 Mar 2024 22:45:36 +0100
> Subject: [PATCH] mm/secretmem: fix GUP-fast succeeding on secretmem folios
>
> folio_is_secretmem() states that secretmem folios cannot be LRU folios:
> so we may only exit early if we find an LRU folio. Yet, we exit early if
> we find a folio that is not a secretmem folio.
>
> Consequently, folio_is_secretmem() fails to detect secretmem folios and,
> therefore, we can succeed in grabbing a secretmem folio during GUP-fast,
> crashing the kernel when we later try reading/writing to the folio, because
> the folio has been unmapped from the directmap.
>
> Reported-by: xingwei lee <xrivendell7@xxxxxxxxx>
> Reported-by: yue sun <samsun1006219@xxxxxxxxx>
> Debugged-by: Miklos Szeredi <miklos@xxxxxxxxxx>
> Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Verified that it's no longer crashing with the reproducers.

Tested-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>