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

From: Maximilian Luz <luzmaximilian@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Bjorn Andersson <andersson@kernel.org>,
	Andy Gross <agross@kernel.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Johan Hovold <johan@kernel.org>,
	Steev Klimaszewski <steev@kali.org>,
	linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/4] lib/ucs2_string: Add UCS-2 strlcpy function
Date: Tue, 30 May 2023 18:15:06 +0200	[thread overview]
Message-ID: <3255010d-82d5-e8e8-2e11-7de25d538d72@gmail.com> (raw)
In-Reply-To: <202305300820.9B2154B@keescook>

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