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Subject: Re: Bug report - slab-out-of-bounds in vcs_scr_readw
To:     Nicolas Pitre <nico@fluxnic.net>
Cc:     Or Cohen <orcohen@paloaltonetworks.com>,
        Greg KH <gregkh@linuxfoundation.org>, textshell@uchuujin.de,
        Daniel Vetter <daniel.vetter@ffwll.ch>, sam@ravnborg.org,
        mpatocka@redhat.com, ghalat@redhat.com,
        linux-kernel@vger.kernel.org, jwilk@jwilk.net,
        Nadav Markus <nmarkus@paloaltonetworks.com>,
        syzkaller@googlegroups.com
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Date:   Tue, 5 Nov 2019 11:29:03 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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On 05. 11. 19, 10:33, Nicolas Pitre wrote:
> Subject: [PATCH] vcs: prevent write access to vcsu devices
> 
> Commit d21b0be246bf ("vt: introduce unicode mode for /dev/vcs") guarded
> against using devices containing attributes as this is not yet
> implemented. It however failed to guard against writes to any devices
> as this is also unimplemented.
> 
> Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
> Cc: <stable@vger.kernel.org> # v4.19+
> 
> diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
> index fa07d79027..ef19b95b73 100644
> --- a/drivers/tty/vt/vc_screen.c
> +++ b/drivers/tty/vt/vc_screen.c
> @@ -456,6 +456,9 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
>  	size_t ret;
>  	char *con_buf;
>  
> +	if (use_unicode(inode))
> +		return -EOPNOTSUPP;

Looks good to me. I am also thinking about a ban directly in open:

if (use_unicode(inode) && (filp->f_flags & O_ACCMODE) != O_RDONLY)
  return -EOPNOTSUPP;

Would that break the unicode users?

thanks,
-- 
js
suse labs