Re: [ 08/12] mac80211: zero initialize count field in ieee80211_tx_rate

Hi Ben,

On Monday 12 March 2012 07:27 AM, Ben Hutchings wrote:

On Mon, 2012-03-12 at 01:20 +0100, Willy Tarreau wrote:

quoted

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Mohammed Shafi Shajakhan<redacted>

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.

true, but i think its better to initialize the count = 0 rather than 
count = 1, though the older version driver checks for rate[i].idx >= 0 
in ath_rc_tx_status. while the ath_tx_status has no such iteration in 
the older driver code.

Ben.

quoted

Cc: stable@vger.kernel.org
Cc: Pavel Roskin<redacted>
Signed-off-by: Mohammed Shafi Shajakhan<redacted>
Signed-off-by: John W. Linville<redacted>

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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-- 
thanks,
shafi