Re: [PATCH] wireless: Compare ethernet addresses by unaligned safe way

[Johannes Berg <johannes@sipsolutions.net>]

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On Sun, 2009-06-28 at 15:18 +0300, Ivan Kuten wrote:
> 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?

Seems alright, but there is more than one instance of this, maybe you
can make a function to allocate a scan request properly and have it be
called from all the places it's needed.

johannes

> 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
> 
> 

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