linux-kernel - Re: [PATCH v4 1/4] lib/ucs2_string: Add UCS-2 strlcpy function

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Date:   Tue, 30 May 2023 18:15:06 +0200
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Johan Hovold <johan@...nel.org>,
        Steev Klimaszewski <steev@...i.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] lib/ucs2_string: Add UCS-2 strlcpy function

On 5/30/23 17:25, Kees Cook wrote:
> On Mon, May 29, 2023 at 01:03:48AM +0200, Maximilian Luz wrote:
>> Add a ucs2_strlcpy() function for UCS-2 strings. The behavior is
>> equivalent to the standard strlcpy() function, just for 16-bit character
>> UCS-2 strings.
> 
> Eek, no. strlcpy() is dangerous in multiple ways[1]. Please implement
> strscpy() (i.e. use strnlen(), negative error on truncation, etc).

Right, make sense, thanks. Somehow I missed that the kernel has a better
function than the C stdlib for that...

> Additionally, it'd be nice of the ucs2 helpers here also implemented the
> rest of the CONFIG_FORTIFY_SOURCE mitigations (i.e. checking for source
> and destination buffer size overflows at compile-time and run-time with
> __builtin_object_size() and __builtin_dynamoc_object_size() respectively).

I can certainly try that, but I think this might be better suited for a
follow-up series, given that we then should also add those to the other
helpers.

Regards,
Max