linux-kernel - Re: [PATCH] dma-buf: Replace strlcpy() with strscpy()

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Message-ID: <4ff92772-9194-42db-b8af-8024e1fdf59f@amd.com>
Date:   Mon, 20 Nov 2023 10:59:45 +0100
From:   Christian König <christian.koenig@....com>
To:     "T.J. Mercier" <tjmercier@...gle.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        linaro-mm-sig@...ts.linaro.org, linux-hardening@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH] dma-buf: Replace strlcpy() with strscpy()

Am 17.11.23 um 19:50 schrieb T.J. Mercier:
> On Thu, Nov 16, 2023 at 11:14 AM Kees Cook <keescook@...omium.org> wrote:
>> strlcpy() reads the entire source buffer first. This read may exceed
>> the destination size limit. This is both inefficient and can lead
>> to linear read overflows if a source string is not NUL-terminated[1].
>> Additionally, it returns the size of the source string, not the
>> resulting size of the destination string. In an effort to remove strlcpy()
>> completely[2], replace strlcpy() here with strscpy().
>>
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
>> Link: https://github.com/KSPP/linux/issues/89 [2]
>> Cc: Sumit Semwal <sumit.semwal@...aro.org>
>> Cc: "Christian König" <christian.koenig@....com>
>> Cc: Azeem Shaikh <azeemshaikh38@...il.com>
>> Cc: linux-media@...r.kernel.org
>> Cc: dri-devel@...ts.freedesktop.org
>> Cc: linaro-mm-sig@...ts.linaro.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: T.J. Mercier <tjmercier@...gle.com>
>
> strscpy returns -E2BIG when it truncates / force null-terminates which
> would provide the wrong argument for dynamic_dname, but
> dma_buf_set_name{_user} makes sure we have a null-terminated string of
> the appropriate maximum size in dmabuf->name.

Thanks for that background check, I was about to note that this might 
not be a good idea.

Linus pretty clearly stated that he doesn't want to see patches like 
that one here, see this article as well. https://lwn.net/Articles/659214/

I think the commit message gives enough reason to merge the patch, so 
I'm going to push it to drm-misc-next. But please make sure to triple 
check stuff like this before sending.

Thanks,
Christian.