Re: [PATCH v3 1/8] of: base: Fix stack overflow in of_parse_phandle_with_args_map()

[Herve Codina <herve.codina@bootlin.com>]

Hi Ernest,

On Tue, 20 Oct 2026 15:00:12 +0200
Ernest Van Hoecke <ernestvanhoecke@gmail.com> wrote:

> From: Ernest Van Hoecke <ernest.vanhoecke@toradex.com>
> 
> of_parse_phandle_with_args_map() reads the #<stem>-cells property of the
> provider referenced by the consumer into list_size. It then copies that
> many cells of the consumer's specifier from out_args->args[] into the
> on-stack initial_match_array[]. Both arrays hold MAX_PHANDLE_ARGS cells,
> but list_size is never checked against that limit. A malformed
> Devicetree with a larger cell count therefore makes the copy read past
> out_args->args[] and write past initial_match_array[].
> 
> The cell count of each provider selected by a <stem>-map entry is
> already rejected when it exceeds MAX_PHANDLE_ARGS. Apply the same limit
> to the provider referenced by the consumer.
> 
> A plain reference to such a provider, without a map, now also fails.
> Previously it succeeded with the specifier truncated to MAX_PHANDLE_ARGS
> cells by __of_parse_phandle_with_args().
> 
> Fixes: bd6f2fd5a1d5 ("of: Support parsing phandle argument lists through a nexus node")
> Suggested-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
> Link: https://lore.kernel.org/all/aq1CSswlo57jZpMH@monoceros/
> Cc: stable@vger.kernel.org
> Signed-off-by: Ernest Van Hoecke <ernest.vanhoecke@toradex.com>
> ---
> v3: New patch (Uwe)
> ---
>  drivers/of/base.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index f63a9486b130..5abadab22392 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -1587,6 +1587,11 @@ int of_parse_phandle_with_args_map(const struct device_node *np,
>  	if (ret < 0)
>  		goto put;
>  
> +	if (list_size > MAX_PHANDLE_ARGS) {
> +		ret = -EINVAL;
> +		goto put;
> +	}
> +

I would be stricter here and avoid the usage of MAX_PHANDLE_ARGS.

First I would check the arrays size to be sure that they are consistent and
then check list_size against the array size.

--- 8< ---
	BUILD_BUG_ON(ARRAY_SIZE(initial_match_array) != ARRAY_SIZE(out_args->args))
	if (list_size > ARRAY_SIZE(initial_match_array)) {
		ret = -EINVAL;
		goto put;
	}
--- 8< ---

IMHO, this is more robust against modification of the 'args' field
definition in struct of_phandle_args or modification of the MAX_PHANDLE_ARGS
value which could lead to some inconsistencies.

Best regards,
Hervé