linux-kernel - Re: [patch] zd1211rw: fix potential array underflow

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Date:	Sat, 27 Feb 2010 15:20:31 +0100
From:	Benoit PAPILLAULT <benoit.papillault@...e.fr>
To:	Dan Carpenter <error27@...il.com>, Daniel Drake <dsd@...too.org>,
	Ulrich Kunitz <kune@...ne-taler.de>,
	"John W. Linville" <linville@...driver.com>,
	Johannes Berg <johannes@...solutions.net>,
	"Luis R. Rodriguez" <lrodriguez@...eros.com>,
	André Goddard Rosa 
	<andre.goddard@...il.com>,
	Benoit PAPILLAULT <benoit.papillault@...e.fr>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] zd1211rw: fix potential array underflow

Dan Carpenter a écrit :
> The first chunk fixes a debugging assert to print a warning about array underflows.
> The second chunk corrects a potential array underflow.  I also removed an assert
> in the second chunk because it can no longer happen.
>
> Signed-off-by: Dan Carpenter <error27@...il.com>
> ---
> This was found by a static check and compile tested only.  Please review carefully.
>
> diff --git a/drivers/net/wireless/zd1211rw/zd_mac.c b/drivers/net/wireless/zd1211rw/zd_mac.c
> index f14deb0..ead2f2c 100644
> --- a/drivers/net/wireless/zd1211rw/zd_mac.c
> +++ b/drivers/net/wireless/zd1211rw/zd_mac.c
> @@ -350,7 +350,7 @@ static void zd_mac_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
>  	first_idx = info->status.rates[0].idx;
>  	ZD_ASSERT(0<=first_idx && first_idx<ARRAY_SIZE(zd_retry_rates));
>  	retries = &zd_retry_rates[first_idx];
> -	ZD_ASSERT(0<=retry && retry<=retries->count);
> +	ZD_ASSERT(1 <= retry && retry <= retries->count);
>   
Note: normal hardware always report a tx_status->retry >= 1. There are 2 
code paths to initialize retry itself : either tx_status is NULL and 
then retry=1 (so we are safe), or tx_status is not NULL and retry = 
tx_status->retry + success >=1 (so we are safe again).

However, I wonder how we should handle if it happens that the HW reports 
a tx_status->retry = 0. I think ZD_ASSERT purpose is to catch 
programming errors, not bogus hardware. Comments?
>  
>  	info->status.rates[0].idx = retries->rate[0];
>  	info->status.rates[0].count = 1; // (retry > 1 ? 2 : 1);
> @@ -360,7 +360,7 @@ static void zd_mac_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
>  		info->status.rates[i].count = 1; // ((i==retry-1) && success ? 1:2);
>  	}
>  	for (; i<IEEE80211_TX_MAX_RATES && i<retry; i++) {
> -		info->status.rates[i].idx = retries->rate[retry-1];
> +		info->status.rates[i].idx = retries->rate[retry - 1];
>  		info->status.rates[i].count = 1; // (success ? 1:2);
>  	}
>  	if (i<IEEE80211_TX_MAX_RATES)
> @@ -424,12 +424,10 @@ void zd_mac_tx_failed(struct urb *urb)
>  		first_idx = info->status.rates[0].idx;
>  		ZD_ASSERT(0<=first_idx && first_idx<ARRAY_SIZE(zd_retry_rates));
>  		retries = &zd_retry_rates[first_idx];
> -		if (retry < 0 || retry > retries->count) {
> +		if (retry <= 0 || retry > retries->count)
>  			continue;
> -		}
>  
> -		ZD_ASSERT(0<=retry && retry<=retries->count);
> -		final_idx = retries->rate[retry-1];
> +		final_idx = retries->rate[retry - 1];
>  		final_rate = zd_rates[final_idx].hw_value;
>  
>  		if (final_rate != tx_status->rate) {
>
>   
Acked-by: Benoit Papillault <benoit.papillault@...e.fr>

Regards,
Benoit

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