linux-kernel - Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to

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Message-ID: <CAHP4M8XfCJ8btBCf42GEZGWm_4ywhPKyXtxoBbHR4U190=gg_A@mail.gmail.com>
Date:   Wed, 10 Nov 2021 14:27:36 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>, kernel@...il.dk,
        David Laight <David.Laight@...lab.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user

>
> Ajay wants to be safe and he thinks, that relying on fact, that
> strlen(func_table[kb_func]) < sizeof(user_kdgkb->kb_string) is not good
> approach, since it's external for vt_do_kdgkb_ioctl. (I hope, I've
> explained his idea in the right way)
>

That's right Pavel.
Every function must work correctly as it "advertises", instead of
relying on "chancy correctness" of the calls leading to the method.