Date: Fri, 6 Jun 2008 22:25:37 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Marc =?iso-8859-1?q?L=F6rner?= <marc.loerner@hob.de> Cc: Peter Jeremy <peterjeremy@optushome.com.au>, freebsd-net@freebsd.org Subject: Re: Probable Bug in tcp.h Message-ID: <20080606221917.A16250@delplex.bde.org> In-Reply-To: <200806061025.37856.marc.loerner@hob.de> References: <200806051712.47048.marc.loerner@hob.de> <200806060930.28527.marc.loerner@hob.de> <20080606075210.GD67629@server.vk2pj.dyndns.org> <200806061025.37856.marc.loerner@hob.de>
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On Fri, 6 Jun 2008, Marc [iso-8859-1] Lörner wrote:
> On Friday 06 June 2008 09:52, Peter Jeremy wrote:
>> I gather from this comment that you have some code using struct tcphdr
>> that is getting alignment errors. struct tcphdr is extensively used
>> in the TCP stack within the kernel so it's likely that any layout or
>> alignment problem with it would show up there. I suspect you are
>> dereferencing a mis-aligned struct tcphdr.
>
> The funny thing is that the dereferencing occurs in
> "/usr/src/sys/netinet/tcp_input.c" in function tcp_input in line 550:
>
> /*
> * Check that TCP offset makes sense,
> * pull out TCP options and adjust length. XXX
> */
> off = th->th_off << 2; <----- here
> if (off < sizeof (struct tcphdr) || off > tlen) {
> tcpstat.tcps_rcvbadoff++;
> goto drop;
> }
>
> So the misalignment may probably lie in TCP stack?
Quite likely. th is normally at offset off0 in ip, where ip is required
to be 32-bit aligned (see my previous reply). You can see off0 in a
stack trace.
Bruce
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