linux-kernel - Re: [PATCH v2] vt: Replace strlcpy with strscpy

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Message-ID: <202309200813.1B0C125@keescook>
Date:   Wed, 20 Sep 2023 08:13:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Azeem Shaikh <azeems@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tony Luck <tony.luck@...el.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v2] vt: Replace strlcpy with strscpy

On Tue, Sep 19, 2023 at 07:21:56PM +0000, Azeem Shaikh wrote:
> strlcpy() reads the entire source buffer first and returns the size of
> the source string, not the destination string, which can be accidentally
> misused [1].
> 
> The copy_to_user() call uses @len returned from strlcpy() directly
> without checking its value. This could potentially lead to read
> overflow. There is no existing bug since @len is always guaranteed to be
> greater than hardcoded strings in @func_table[kb_func]. But as written
> it is very fragile and specifically uses a strlcpy() result without sanity
> checking and using it to copy to userspace.
> 
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with strscpy().
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
> 
> Signed-off-by: Azeem Shaikh <azeems@...gle.com>
> ---
> v2:
>  * Return -ENOSPC instead of -EFAULT in case of truncation.
>  * Update commit log to clarify that there is no exploitable bug but instead the code uses a fragile anti-pattern.

Changes look good. Thanks!

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook