linux-kernel - Re: [ 08/12] mac80211: zero initialize count field in ieee80211_tx

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Date:	Mon, 12 Mar 2012 01:57:52 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Willy Tarreau <w@....eu>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Pavel Roskin <proski@....org>,
	Mohammed Shafi Shajakhan <mohammed@....qualcomm.com>,
	"John W. Linville" <linville@...driver.com>
Subject: Re: [ 08/12] mac80211: zero initialize count field in
 ieee80211_tx_rate

On Mon, 2012-03-12 at 01:20 +0100, Willy Tarreau wrote:
> 2.6.32-longterm review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Mohammed Shafi Shajakhan <mohammed@....qualcomm.com>
> 
> commit 8617b093d0031837a7be9b32bc674580cfb5f6b5 upstream.
> 
> rate control algorithms concludes the rate as invalid
> with rate[i].idx < -1 , while they do also check for rate[i].count is
> non-zero. it would be safer to zero initialize the 'count' field.
> recently we had a ath9k rate control crash where the ath9k rate control
> in ath_tx_status assumed to check only for rate[i].count being non-zero
> in one instance and ended up in using invalid rate index for
> 'connection monitoring NULL func frames' which eventually lead to the crash.
> thanks to Pavel Roskin for fixing it and finding the root cause.
> https://bugzilla.redhat.com/show_bug.cgi?id=768639

In 2.6.32, ath_tx_status() checks that rates[i].idx >= 0, so it properly
ignores these dummy entries.  Further, there is code further down the
rate_control_get_rate() function that sets .idx only and appears to
depend on the initialisation of .count = 1.

So I'm pretty sure this patch is wrong for 2.6.32; it could be
backported but I don't think the change is necessary anyway.

Ben.

> Cc: stable@...r.kernel.org
> Cc: Pavel Roskin <proski@....org>
> Signed-off-by: Mohammed Shafi Shajakhan <mohammed@....qualcomm.com>
> Signed-off-by: John W. Linville <linville@...driver.com>
> 
> diff --git a/net/mac80211/rate.c b/net/mac80211/rate.c
> index ad64f4d..f9b8e81 100644
> --- a/net/mac80211/rate.c
> +++ b/net/mac80211/rate.c
> @@ -344,7 +344,7 @@ void rate_control_get_rate(struct ieee80211_sub_if_data *sdata,
>  	for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
>  		info->control.rates[i].idx = -1;
>  		info->control.rates[i].flags = 0;
> -		info->control.rates[i].count = 1;
> +		info->control.rates[i].count = 0;
>  	}
>  
>  	if (sdata->local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL)
> 
> 
> --
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> 

-- 
Ben Hutchings
Life would be so much easier if we could look at the source code.

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