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Message-ID: <2b9fa498-e099-4987-89d3-dd1a5df24705@blemings.org>
Date:   Tue, 17 Oct 2023 09:18:38 +1100
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Subject: Re: [PATCH] hamradio: replace deprecated strncpy with strscpy
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To:     Kees Cook <kees@kernel.org>,
        Dan Carpenter <dan.carpenter@linaro.org>,
        Simon Horman <horms@kernel.org>
Cc:     Justin Stitt <justinstitt@google.com>,
        Thomas Sailer <t.sailer@alumni.ethz.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-hams@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org
References: <20231012-strncpy-drivers-net-hamradio-baycom_epp-c-v1-1-8f4097538ee4@google.com>
 <20231015150619.GC1386676@kernel.org>
 <ede96908-76ff-473c-a5e1-39e2ce130df9@kadam.mountain>
 <FA371CE1-F449-44D4-801A-11C842E84867@kernel.org>
 <123F9651-9469-4F2B-ADC1-12293C9EA7FE@kernel.org>
From:   Hugh Blemings <hugh@blemings.org>
In-Reply-To: <123F9651-9469-4F2B-ADC1-12293C9EA7FE@kernel.org>
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On 17/10/23 04:03, Kees Cook wrote:
> 
> 
> On October 16, 2023 10:01:20 AM PDT, Kees Cook <kees@kernel.org> wrote:
>>
>>
>> On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@linaro.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.  ;)