From: Frank Cusack <fcusack@fcusack.com>
To: Menno Smits <menno@netbox.biz>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Kernel panic with pptpd when mss > mtu
Date: Tue, 20 May 2003 21:43:01 -0700 [thread overview]
Message-ID: <20030520214301.A3632@google.com> (raw)
In-Reply-To: <20030521091442.1bfb41b6.menno@netbox.biz>; from menno@netbox.biz on Wed, May 21, 2003 at 09:14:42AM +1000
On Wed, May 21, 2003 at 09:14:42AM +1000, Menno Smits wrote:
> I'm seeing a kernel oops with 2.4.20 which seems to be related to the
> PopTop PPTP server. When certain clients connect in (seems to be
> Win98) and begin large data transfers the kernel will reliably oops.
> The system crashes hard, the oops doesn't make it to the logs.
...
> I have been able to deal with the issue by using the workaround
> suggested in the the second post. That is, adding netfilter rules with
> the TCPMSS target to limit the TCP MSS to PMTU - 40. Apparently the
> problem is triggered by the MSS being bigger than the MTU (which is
> 750 in this case).
Yup. win98 ignores the negotiated MRU from the PPP peer (MTU on the win98
side) and sends PPP packets larger than MTU. As you've discovered. :-)
Linux doesn't allocate enough space for the decompressor output, and the
mppe module doesn't properly check that enough space exists. (That's
because PPP MPPE packets *shrink* after "decompression", and the mppe
module assumes at least the same amount of space as the PPP packet is
allocated for the decompressor.)
Grab the latest ftp://ftp.samba.org/pub/unpacked/ppp which corrects both
of the above problems.
I'll be posting a patch to lkml to correct the decompressor allocation
problem, shortly (a few weeks).
/fc
next prev parent reply other threads:[~2003-05-21 8:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-20 23:14 Kernel panic with pptpd when mss > mtu Menno Smits
2003-05-21 4:43 ` Frank Cusack [this message]
2003-05-21 8:09 ` Menno Smits
2003-05-22 5:10 ` Menno Smits
2003-05-21 6:41 ` Jochen Friedrich
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