Re: [PATCH net v3 2/3] ieee802154: ca8210: prevent stack buffer overflow in hwme_get_request_sync()

[Miquel Raynal <miquel.raynal@bootlin.com>]

> Initialize lenvar = 1 in ca8210_get_ed() and return
> IEEE802154_SYSTEM_ERROR in hwme_get_request_sync() if
> response.pdata.hwme_get_cnf.hw_attribute_length exceeds
> *hw_attribute_length.

The relationship is not obvious to me.

> Tested in QEMU with KASAN enabled by passing an oversized
> hw_attribute_length response into ca8210_get_ed().
>
> Fixes: ded845a781a5 ("ieee802154: Add CA8210 IEEE 802.15.4 device driver")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
> Changes in v3:
> - No changes.
>
> Changes in v2:
> - Split out as patch 2/3.
> - Replaced the temporary stack buffer in ca8210_get_ed() with lenvar = 1
>   and an upper-bound check against *hw_attribute_length in
>   hwme_get_request_sync() as requested by Miquel Raynal.
>
>  drivers/net/ieee802154/ca8210.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ieee802154/ca8210.c b/drivers/net/ieee802154/ca8210.c
> index a990a0f..8aa7ffe 100644
> --- a/drivers/net/ieee802154/ca8210.c
> +++ b/drivers/net/ieee802154/ca8210.c
> @@ -1677,6 +1677,9 @@ static u8 hwme_get_request_sync(
>  		return IEEE802154_SYSTEM_ERROR;
>  
>  	if (response.pdata.hwme_get_cnf.status == IEEE802154_SUCCESS) {
> +		if (response.pdata.hwme_get_cnf.hw_attribute_length >
> +		    *hw_attribute_length)
> +			return IEEE802154_SYSTEM_ERROR;

Why is hw_attribute_length use here before being set (or re-set) just
below?

The organization of this patch is weird.

Miquèl