linux-kernel - Re: [PATCH] clk: samsung: exynos-clkout: Assign .num before accessing .hws

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Message-ID: <202511241115.0E974A2C@keescook>
Date: Mon, 24 Nov 2025 11:15:12 -0800
From: Kees Cook <kees@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Salvatore Bonaccorso <carnil@...ian.org>,
	linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org, stable@...r.kernel.org,
	Jochen Sprickerhof <jochen@...ickerhof.de>
Subject: Re: [PATCH] clk: samsung: exynos-clkout: Assign .num before
 accessing .hws

On Mon, Nov 24, 2025 at 12:11:06PM -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 (UBSAN_BOUNDS)
> 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 exynos_clkout_probe() due to .num being assigned after .hws[]
> has been accessed:
> 
>   UBSAN: array-index-out-of-bounds in drivers/clk/samsung/clk-exynos-clkout.c:178:18
>   index 0 is out of range for type 'clk_hw *[*]'
> 
> Move the .num initialization to before the first access of .hws[],
> clearing up the warning.
> 
> Cc: stable@...r.kernel.org
> Fixes: f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
> Reported-by: Jochen Sprickerhof <jochen@...ickerhof.de>
> Closes: https://lore.kernel.org/aSIYDN5eyKFKoXKL@eldamar.lan/
> Tested-by: Jochen Sprickerhof <jochen@...ickerhof.de>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook