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

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Date:   Tue, 30 May 2023 08:25:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Maximilian Luz <luzmaximilian@...il.com>
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 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).
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).

-Kees

[1] https://docs.kernel.org/process/deprecated.html#strlcpy

-- 
Kees Cook