linux-hardening - Re: [PATCH v2] hamradio: replace deprecated strncpy with strscpy

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Date: Mon, 16 Oct 2023 21:58:36 +0200
From: Simon Horman <horms@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Justin Stitt <justinstitt@...gle.com>,
	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 v2] hamradio: replace deprecated strncpy with strscpy_pad

On Mon, Oct 16, 2023 at 12:42:22PM -0700, Kees Cook wrote:
> On Mon, Oct 16, 2023 at 06:42:42PM +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 based on 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)))
> > 
> > Considering the above, a suitable replacement is strscpy_pad() as it
> > guarantees NUL-termination on the destination buffer while also
> > NUL-padding (which is good+wanted behavior when copying data to
> > userspace).
> > 
> > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> > Link: https://github.com/KSPP/linux/issues/90
> > Cc: linux-hardening@...r.kernel.org
> > Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> 
> Thanks!
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>

Likewise, thanks. I prefer this over v1.

Reviewed-by: Simon Horman <horms@...nel.org>