Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Kees Cook]

On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@xxxxxxxxxx> 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