linux-kernel - Re: [PATCH][next] media: venus: hfi_cmds: Replace one-element array with flex-array member and use __counted

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Date:   Mon, 9 Oct 2023 12:52:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
        Vikash Garodia <quic_vgarodia@...cinc.com>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] media: venus: hfi_cmds: Replace one-element array
 with flex-array member and use __counted_by

On Mon, Oct 09, 2023 at 12:42:05PM -0600, Gustavo A. R. Silva wrote:
> Array `data` in `struct hfi_sfr` is being used as a fake flexible array
> at run-time:
> 
> drivers/media/platform/qcom/venus/hfi_venus.c:
> 1033         p = memchr(sfr->data, '\0', sfr->buf_size);
> 1034         /*
> 1035          * SFR isn't guaranteed to be NULL terminated since SYS_ERROR indicates
> 1036          * that Venus is in the process of crashing.
> 1037          */
> 1038         if (!p)
> 1039                 sfr->data[sfr->buf_size - 1] = '\0';
> 1040
> 1041         dev_err_ratelimited(dev, "SFR message from FW: %s\n", sfr->data);
> 
> Fake flexible arrays are deprecated, and should be replaced by
> flexible-array members. So, replace one-element array with a
> flexible-array member in `struct hfi_sfr`.
> 
> While there, also annotate array `data` with __counted_by() to 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).
> 
> This results in no differences in binary output.

Thanks for checking!

> 
> This issue was found with the help of Coccinelle, and audited and fixed
> manually.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

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

-- 
Kees Cook