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

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Message-ID: <123F9651-9469-4F2B-ADC1-12293C9EA7FE@kernel.org>
Date:   Mon, 16 Oct 2023 10:03:57 -0700
From:   Kees Cook <kees@...nel.org>
To:     Dan Carpenter <dan.carpenter@...aro.org>,
        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 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. ;)

-- 
Kees Cook