Re: [syzbot] [overlayfs?] general protection fault in ovl_llseek

[Amir Goldstein]

On Fri, Sep 27, 2024 at 9:10 AM Leo Stone <leocstone@xxxxxxxxx> wrote:
>
> Add a check to avoid using an invalid pointer if ovl_open_realfile fails.
>
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 2b7a5a3a7a2f..67f75eeb1e51 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -117,7 +117,11 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
>                 struct file *f = ovl_open_realfile(file, &realpath);
>                 if (IS_ERR(f))
>                         return PTR_ERR(f);
> -               real->word = (unsigned long)ovl_open_realfile(file, &realpath) | FDPUT_FPUT;
> +               f = ovl_open_realfile(file, &realpath);
> +               if (IS_ERR(f))
> +                       return PTR_ERR(f);
> +               real->word = (unsigned long)f;
> +               real->word |= FDPUT_FPUT;
>                 return 0;
>         }
>
>

No, that's the wrong fix.
There is a braino and a file leak in this code.

Linus,

Could you apply this braino fix manually before releasing rc1.

Thanks,
Amir.
From 994d5a61855da275292780af72948d7207025ec8 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@xxxxxxxxx>
Date: Fri, 27 Sep 2024 13:54:23 +0200
Subject: [PATCH] ovl: fix file leak in ovl_real_fdget_meta()

ovl_open_realfile() is wrongly called twice after conversion to
new struct fd.

Fixes: ("88a2f6468d01 struct fd: representation change")
Reported-by: syzbot+d9efec94dcbfa0de1c07@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 fs/overlayfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 2b7a5a3a7a2f..4504493b20be 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -117,7 +117,7 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
 		struct file *f = ovl_open_realfile(file, &realpath);
 		if (IS_ERR(f))
 			return PTR_ERR(f);
-		real->word = (unsigned long)ovl_open_realfile(file, &realpath) | FDPUT_FPUT;
+		real->word = (unsigned long)f | FDPUT_FPUT;
 		return 0;
 	}
 
-- 
2.34.1