linux-hardening - Re: [PATCH 2/2] clk: bcm: rpi: Assign ->num before accessing ->hws

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Message-ID: <202404251015.46D8BE1F1@keescook>
Date: Thu, 25 Apr 2024 10:15:57 -0700
From: Kees Cook <keescook@...omium.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	bcm-kernel-feedback-list@...adcom.com, linux-clk@...r.kernel.org,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-hardening@...r.kernel.org, patches@...ts.linux.dev,
	llvm@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] clk: bcm: rpi: Assign ->num before accessing ->hws

On Thu, Apr 25, 2024 at 09:55:52AM -0700, Nathan Chancellor wrote:
> Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
> __counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
> with __counted_by, which informs the bounds sanitizer about the number
> of elements in hws, so that it can warn when hws is accessed out of
> bounds. As noted in that change, the __counted_by member must be
> initialized with the number of elements before the first array access
> happens, otherwise there will be a warning from each access prior to the
> initialization because the number of elements is zero. This occurs in
> raspberrypi_discover_clocks() due to ->num being assigned after ->hws
> has been accessed:
> 
>   UBSAN: array-index-out-of-bounds in drivers/clk/bcm/clk-raspberrypi.c:374:4
>   index 3 is out of range for type 'struct clk_hw *[] __counted_by(num)' (aka 'struct clk_hw *[]')
> 
> Move the ->num initialization to before the first access of ->hws, which
> clears up the warning.
> 
> Cc: stable@...r.kernel.org
> Fixes: f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Looks good; thanks!

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

-- 
Kees Cook