linux-kernel - Re: [PATCH 04/22] firmware: arm_scmi: Validate BASE_DISCOVER_LIST

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Message-ID: <20220428100729.qlzl5lkkn2r5u3ra@bogus>
Date:   Thu, 28 Apr 2022 11:07:29 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        james.quinlan@...adcom.com, Jonathan.Cameron@...wei.com,
        f.fainelli@...il.com, etienne.carriere@...aro.org,
        vincent.guittot@...aro.org, souvik.chakravarty@....com
Subject: Re: [PATCH 04/22] firmware: arm_scmi: Validate
 BASE_DISCOVER_LIST_PROTOCOLS reply

On Wed, Mar 30, 2022 at 04:05:33PM +0100, Cristian Marussi wrote:
> Do not blindly trust SCMI backend server reply about list of implemented
> protocols, instead validate the reported length of the list of protocols
> against the real payload size of the message reply.
>
> Fixes: b6f20ff8bd9 ("firmware: arm_scmi: add common infrastructure and support for base protocol")
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
>  drivers/firmware/arm_scmi/base.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/drivers/firmware/arm_scmi/base.c b/drivers/firmware/arm_scmi/base.c
> index f279146f8110..c1165d1282ef 100644
> --- a/drivers/firmware/arm_scmi/base.c
> +++ b/drivers/firmware/arm_scmi/base.c
> @@ -189,6 +189,9 @@ scmi_base_implementation_list_get(const struct scmi_protocol_handle *ph,
>  	list = t->rx.buf + sizeof(*num_ret);
>
>  	do {
> +		size_t real_list_sz;
> +		u32 calc_list_sz;
> +
>  		/* Set the number of protocols to be skipped/already read */
>  		*num_skip = cpu_to_le32(tot_num_ret);
>
> @@ -202,6 +205,24 @@ scmi_base_implementation_list_get(const struct scmi_protocol_handle *ph,
>  			break;
>  		}
>
> +		if (t->rx.len < (sizeof(u32) * 2)) {
> +			dev_err(dev, "Truncated reply - rx.len:%zd\n",
> +				t->rx.len);
> +			ret = -EPROTO;
> +			break;
> +		}
> +
> +		real_list_sz = t->rx.len - sizeof(u32);
> +		calc_list_sz = ((loop_num_ret / sizeof(u32)) +
> +				!!(loop_num_ret % sizeof(u32))) * sizeof(u32);

Any reason this can't be (loop_num_ret - 1) / sizeof(u32) + 1 ?

--
Regards,
Sudeep