linux-kernel - Re: [PATCH 3/3] vt: keyboard, extend func_buf

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Message-ID: <20201016132044.GA1798163@kroah.com>
Date:   Fri, 16 Oct 2020 15:20:44 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Minh Yuan <yuanmingbuaa@...il.com>
Subject: Re: [PATCH 3/3] vt: keyboard, extend func_buf_lock to readers

On Fri, Oct 16, 2020 at 02:24:12PM +0200, Jiri Slaby wrote:
> Both read-side users of func_table/func_buf need locking. Without that,
> one can easily confuse the code by repeatedly setting altering strings
> like:
> while (1)
> 	for (a = 0; a < 2; a++) {
> 		struct kbsentry kbs = {};
> 		strcpy((char *)kbs.kb_string, a ? ".\n" : "88888\n");
> 		ioctl(fd, KDSKBSENT, &kbs);
> 	}
> 
> When that program runs, one can get unexpected output by holding F1
> (note the unxpected period on the last line):
> .
> 88888
> .8888
> 
> So protect all accesses to 'func_table' (and func_buf) by preexisting
> 'func_buf_lock'.
> 
> It is easy in 'k_fn' handler as 'puts_queue' is expected not to sleep.
> On the other hand, KDGKBSENT needs a local (atomic) copy of the string
> because copy_to_user can sleep.
> 
> Likely fixes CVE-2020-25656.
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Reported-by: Minh Yuan <yuanmingbuaa@...il.com>
> ---
>  drivers/tty/vt/keyboard.c | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)

So all 3 of these should go to 5.10-final?

thanks,

greg k-h