From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brandon Craig Rhodes Subject: Re: TKIP encryption should allocate enough tailroom Date: Wed, 17 Jan 2007 12:38:44 -0500 Message-ID: <87odox4kpn.fsf@ten22.rhodesmill.org> References: <87bqky759v.fsf@ten22.rhodesmill.org> <87mz4h61p0.fsf@ten22.rhodesmill.org> <45AE5B8C.2070407@lwfinger.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org Return-path: Received: from 66-23-211-138.clients.speedfactory.net ([66.23.211.138]:42497 "EHLO ten22.rhodesmill.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932600AbXAQRip (ORCPT ); Wed, 17 Jan 2007 12:38:45 -0500 To: Larry Finger In-Reply-To: <45AE5B8C.2070407@lwfinger.net> (Larry Finger's message of "Wed, 17 Jan 2007 11:23:24 -0600") Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Larry Finger writes: > Brandon Craig Rhodes wrote: > >> Having further reviewed my code, I have changed my mind; the >> ieee80211_crypt_tkip routines are not designed to be responsible for >> creating enough headroom and tailroom. The "hostap" driver should be >> doing this. > > This makes sense. I have used the bcm43xx driver with WPA-PSK TKIP > encryption for at least a year, and I have never seen this error. >>From what I can tell, even people using the "hostap" driver never see this error! The kernel must allocate such large skb's in normal operation that there is always more than enough tailroom for twelve bytes of TKIP encryption. In my case, packets are arriving on the physical machine from a Xen virtual machine that the physical machine is hosting. The Xen code receiving the packets must allocate much tighter skb's than does the normal kernel code that receives packets from hardware. (Perhaps because Xen knows the packet size ahead of time, whereas hardware drivers do not?) Searching for the error message: kernel: Invalid packet for Michael MIC add (tailroom=6 hdr_len=24 skb->len=92) on Google returned, if I recall, only references to the kernel source code itself - which always gives me the sinking feeling that I've gotten myself into a configuration shared with no one else on earth! -- Brandon Craig Rhodes brandon@rhodesmill.org http://rhodesmill.org/brandon