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Date: Sun, 28 Jun 2009 15:18:10 +0300
From: Ivan Kuten <ivan.kuten@promwad.com>
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To: linux-wireless@vger.kernel.org
CC: Johannes Berg <johannes@sipsolutions.net>,
	Yauhen Kharuzhy <yauhen.kharuzhy@promwad.com>
Subject: Re: [PATCH] wireless: Compare ethernet addresses by unaligned safe
 way
References: <1245149672-18063-1-git-send-email-yauhen.kharuzhy@promwad.com> <1245150895.8623.3.camel@johannes.local>
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Hello,

In net/wireless/scan.c : cfg80211_wext_siwscan there seems also unaligned allocations
for creq->ssids and creq->channels. Should it be something like that?

Modified: trunk/uClinux-dist-2008R1-RC8/compat-wireless-2009-06-11/net/wireless/scan.c
==============================================================================
--- trunk/uClinux-dist-2008R1-RC8/compat-wireless-2009-06-11/net/wireless/scan.c (original)
+++ trunk/uClinux-dist-2008R1-RC8/compat-wireless-2009-06-11/net/wireless/scan.c Fri Jun 26 14:00:52 2009
@@ -619,7 +619,7 @@
 		if (wiphy->bands[band])
 			n_channels += wiphy->bands[band]->n_channels;

-	creq = kzalloc(sizeof(*creq) + sizeof(struct cfg80211_ssid) +
+	creq = kzalloc(roundup(sizeof(*creq), 4) + roundup(sizeof(struct cfg80211_ssid), 4) +
 		       n_channels * sizeof(void *),
 		       GFP_ATOMIC);
 	if (!creq) {
@@ -629,8 +629,8 @@

 	creq->wiphy = wiphy;
 	creq->ifidx = dev->ifindex;
-	creq->ssids = (void *)(creq + 1);
-	creq->channels = (void *)(creq->ssids + 1);
+	creq->ssids = (void *)creq + roundup(sizeof(*creq), 4);
+	creq->channels = (void *)creq->ssids + roundup(sizeof(*creq->ssids), 4);
 	creq->n_channels = n_channels;
 	creq->n_ssids = 1;

Regards,
Ivan

> On Tue, 2009-06-16 at 13:54 +0300, Yauhen Kharuzhy wrote:
>> When we try to run RTL8187 driver on AD BlackFin platform, we got
>> messages from kernel about unaligned memory access at
>> compare_ether_addr() calls.
>>
>> Replacing of compare_ether_addr() by memcmp() fixes this problem.
> 
> This shouldn't be necessary. Which operand is unaligned?
> 
>> --- a/net/mac80211/ibss.c
>> +++ b/net/mac80211/ibss.c
>> @@ -395,7 +395,7 @@ struct sta_info *ieee80211_ibss_add_sta(struct ieee80211_sub_if_data *sdata,
>>  		return NULL;
>>  	}
>>  
>> -	if (compare_ether_addr(bssid, sdata->u.ibss.bssid))
>> +	if (memcmp(bssid, sdata->u.ibss.bssid, ETH_ALEN))
>>  		return NULL;
> 
> So in this case it seems that it is possible that u.ibss.bssid is not
> aligned, consider fixing by doing
> 
> --- ieee80211_i.h
> +++ ieee80211_i.h
> -	u8 bssid[ETH_ALEN];
> +	u8 bssid[ETH_ALEN] __align(2);
> 
> or so instead.
>  
>> --- a/net/wireless/scan.c
>> +++ b/net/wireless/scan.c
>> @@ -134,7 +134,7 @@ static bool is_bss(struct cfg80211_bss *a,
>>  {
>>  	const u8 *ssidie;
>>  
>> -	if (bssid && compare_ether_addr(a->bssid, bssid))
>> +	if (bssid && memcmp(a->bssid, bssid, ETH_ALEN))
> 
> Since a->bssid is after a pointer I can't see how it would be unaligned,
> and bssid should be unaligned only if the call trace shows it's coming
> from the above u.ibss.bssid.
> 
> johannes