linux-kernel - Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

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Date:   Mon, 16 Oct 2023 15:20:39 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Hugh Blemings <hugh@...mings.org>
Cc:     Kees Cook <kees@...nel.org>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Simon Horman <horms@...nel.org>,
        Thomas Sailer <t.sailer@...mni.ethz.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-hams@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

On Mon, Oct 16, 2023 at 3:18 PM Hugh Blemings <hugh@...mings.org> wrote:
>
>
>
> On 17/10/23 04:03, Kees Cook wrote:
> >
> >
> > On October 16, 2023 10:01:20 AM PDT, Kees Cook <kees@...nel.org> wrote:
> >>
> >>
> >> On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@...aro.org> wrote:
> >>> On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
> >>>> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
> >>>>> strncpy() is deprecated for use on NUL-terminated destination strings
> >>>>> [1] and as such we should prefer more robust and less ambiguous string
> >>>>> interfaces.
> >>>>>
> >>>>> We expect both hi.data.modename and hi.data.drivername to be
> >>>>> NUL-terminated but not necessarily NUL-padded which is evident by its
> >>>>> usage with sprintf:
> >>>>> |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
> >>>>> |               bc->cfg.intclk ? "int" : "ext",
> >>>>> |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
> >>>>> |               bc->cfg.loopback ? ",loopback" : "");
> >>>>>
> >>>>> Note that this data is copied out to userspace with:
> >>>>> |       if (copy_to_user(data, &hi, sizeof(hi)))
> >>>>> ... however, the data was also copied FROM the user here:
> >>>>> |       if (copy_from_user(&hi, data, sizeof(hi)))
> >>>>
> >>>> Thanks Justin,
> >>>>
> >>>> I see that too.
> >>>>
> >>>> Perhaps I am off the mark here, and perhaps it's out of scope for this
> >>>> patch, but I do think it would be nicer if the kernel only sent
> >>>> intended data to user-space, even if any unintended payload came
> >>>> from user-space.
> >>>>
> >>>
> >>> It's kind of normal to pass user space data back to itself.  We
> >>> generally only worry about info leaks.
> >>
> >> True but since this used to zero the rest of the buffet, let's just keep that behavior and use strscpy_pad().
> >
> > I'm calling all byte arrays a "buffet" from now on. ;)
> >
> A tasteful change to the sauce I think.  ;)

Just perfect that this is happening on a **ham**radio driver.