Subject: Re: [PATCH] wireless: Compare ethernet addresses by unaligned safe
 way
From: Johannes Berg <johannes@sipsolutions.net>
To: Yauhen Kharuzhy <yauhen.kharuzhy@promwad.com>
Cc: linux-wireless@vger.kernel.org
In-Reply-To: <1245149672-18063-1-git-send-email-yauhen.kharuzhy@promwad.com>
References: <1245149672-18063-1-git-send-email-yauhen.kharuzhy@promwad.com>
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Date: Tue, 16 Jun 2009 13:14:55 +0200
Message-Id: <1245150895.8623.3.camel@johannes.local>
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Sender: linux-wireless-owner@vger.kernel.org


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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.
>=20
> 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 ieee80=
211_sub_if_data *sdata,
>  		return NULL;
>  	}
> =20
> -	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.
=20
> --- 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;
> =20
> -	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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