Re: [PATCH 01/32] staging: wfx: add sanity checks to hif_join()

From: Dan Carpenter <dan.carpenter@oracle.com>
To: Jerome Pouiller <Jerome.Pouiller@silabs.com>
Cc: devel@driverdev.osuosl.org, linux-wireless@vger.kernel.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"David S . Miller" <davem@davemloft.net>,
	Kalle Valo <kvalo@codeaurora.org>
Subject: Re: [PATCH 01/32] staging: wfx: add sanity checks to hif_join()
Date: Thu, 2 Apr 2020 15:42:23 +0300	[thread overview]
Message-ID: <20200402124223.GQ2001@kadam> (raw)
In-Reply-To: <20200401110405.80282-2-Jerome.Pouiller@silabs.com>

On Wed, Apr 01, 2020 at 01:03:34PM +0200, Jerome Pouiller wrote:
> From: Jérôme Pouiller <jerome.pouiller@silabs.com>
> 
> Add a few check on start of hif_join().
> 
> Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
> ---
>  drivers/staging/wfx/hif_tx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/staging/wfx/hif_tx.c b/drivers/staging/wfx/hif_tx.c
> index 77bca43aca42..445906035e9d 100644
> --- a/drivers/staging/wfx/hif_tx.c
> +++ b/drivers/staging/wfx/hif_tx.c
> @@ -297,6 +297,8 @@ int hif_join(struct wfx_vif *wvif, const struct ieee80211_bss_conf *conf,
>  	struct hif_req_join *body = wfx_alloc_hif(sizeof(*body), &hif);
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
We've got an allocation here.  It's a mistake to put the allocation in
the declaration block because you're going to forget to check for
failure.

>  
>  	WARN_ON(!conf->basic_rates);
> +	WARN_ON(sizeof(body->ssid) < ssidlen);

Put the variable on the left.  WARN_ON(ssidlen > sizeof(body->ssid)).
I'm not a big fan of adding this sort of debug code, just audit the
callers to see if it's possible or not.

I have audited the caller for you, and I believe that this condition
*is possible* so we need to return -EINVAL in this situation to prevent
memory corruption.

	if (ssidlen > sizeof(body->ssid))
		return -EINVAL;

> +	WARN(!conf->ibss_joined && !ssidlen, "joining an unknown BSS");
>  	body->infrastructure_bss_mode = !conf->ibss_joined;
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Potential NULL dererefence because of the unchecked allocation.

regards,
dan carpenter