linux-kernel - Re: [PATCH 3/5] usb: fotg210-hcd: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <CACRpkdbvncOsbG2W3vJJz8N4mH8XCqyf_Ny1_hsLwK4P+7x1Cw@mail.gmail.com>
Date:   Thu, 30 Nov 2023 15:48:27 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Lee Jones <lee@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Yuan-Hsin Chen <yhchen@...aday-tech.com>,
        Feng-Hsin Chiang <john453@...aday-tech.com>,
        Po-Yu Chuang <ratbert.chuang@...il.com>,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH 3/5] usb: fotg210-hcd: Replace snprintf() with the safer
 scnprintf() variant

On Thu, Nov 30, 2023 at 11:55 AM Lee Jones <lee@...nel.org> wrote:

> There is a general misunderstanding amongst engineers that {v}snprintf()
> returns the length of the data *actually* encoded into the destination
> array.  However, as per the C99 standard {v}snprintf() really returns
> the length of the data that *would have been* written if there were
> enough space for it.  This misunderstanding has led to buffer-overruns
> in the past.  It's generally considered safer to use the {v}scnprintf()
> variants in their place (or even sprintf() in simple cases).  So let's
> do that.
>
> The uses in this file both seem to assume that data *has been* written!
>
> Link: https://lwn.net/Articles/69419/
> Link: https://github.com/KSPP/linux/issues/105
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Yuan-Hsin Chen <yhchen@...aday-tech.com>
> Cc: Feng-Hsin Chiang <john453@...aday-tech.com>
> Cc: Po-Yu Chuang <ratbert.chuang@...il.com>
> Cc: linux-usb@...r.kernel.org
> Signed-off-by: Lee Jones <lee@...nel.org>

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Thanks for doing this Lee!

And as David points out it is even a bug fix at the same time.

Yours,
Linus Walleij