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

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Message-ID: <ede96908-76ff-473c-a5e1-39e2ce130df9@kadam.mountain>
Date:   Mon, 16 Oct 2023 08:47:53 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Simon Horman <horms@...nel.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] hamradio: replace deprecated strncpy with strscpy

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.

regards,
dan carpenter