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Date: Mon, 16 Oct 2023 10:01:20 -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 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().

-Kees

-- 
Kees Cook

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