linux-kernel - Re: [PATCH][next] staging: greybus: Add __counted_by for struct apr_rx_buf and use struct

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Message-ID: <202310091608.C892CFA@keescook>
Date:   Mon, 9 Oct 2023 16:08:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] staging: greybus: Add __counted_by for struct
 apr_rx_buf and use struct_size()

On Mon, Oct 09, 2023 at 03:52:59PM -0600, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
> 
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks right, "len" is updated before accessing "data[]".

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

-- 
Kees Cook