linux-kernel - Re: [syzbot] [overlayfs?] general protection fault in ovl

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Message-ID: <CAOQ4uxhXbTZS3wmLibit-vP_3yQSC=p+qmBLxKkBHL1OgO5NBQ@mail.gmail.com>
Date: Fri, 27 Sep 2024 14:03:07 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Leo Stone <leocstone@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>
Cc: syzbot+d9efec94dcbfa0de1c07@...kaller.appspotmail.com, 
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	miklos@...redi.hu, syzkaller-bugs@...glegroups.com, skhan@...uxfoundation.org, 
	anupnewsmail@...il.com, Christian Brauner <brauner@...nel.org>, 
	Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [syzbot] [overlayfs?] general protection fault in ovl_llseek

On Fri, Sep 27, 2024 at 9:10 AM Leo Stone <leocstone@...il.com> 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.

View attachment "0001-ovl-fix-file-leak-in-ovl_real_fdget_meta.patch" of type "text/x-patch" (1043 bytes)