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Date: Thu, 30 Jun 2011 11:06:23 +0200 From: Steffen Klassert <steffen.klassert@...unet.com> To: David Miller <davem@...emloft.net> Cc: eric.dumazet@...il.com, herbert@...dor.hengli.com.au, netdev@...r.kernel.org Subject: Re: [PATCH 2/3] ipv4: Fix packet size calculation for IPsec packets in __ip_append_data On Mon, Jun 27, 2011 at 08:39:38PM -0700, David Miller wrote: > From: Steffen Klassert <steffen.klassert@...unet.com> > Date: Wed, 22 Jun 2011 13:02:19 +0200 > > > While reading through the code of __ip_append_data() I noticed that we > > might use ip_ufo_append_data() for packets that will be IPsec transformed > > later, is this ok? I don't know how ufo handling works, but I would guess > > that it expects an udp header and not an IPsec header as the packets > > transport header. > > Indeed, it could be a real problem. Ok, so I'll send a patch to fix it up. > > > The IPsec mtu is 1438 here, so the first packet is too big. > > xfrm4_tunnel_check_size() notices this and sends a ICMP_FRAG_NEEDED > > packet that announces a mtu of 1438 to the original sender of the ping > > packet. Unfortunately the sender is a local address, it's the IPsec > > tunnel entry point. So we update the mtu for this connection to 1438. > > Now, with the next packet xfrm_bundle_ok() notices that the path mtu has > > changed, so it subtracts the IPsec overhead from the mtu a second time > > and we end up with a mtu of 1374. This game goes until we reach a minimal > > mtu of 494. > > > > Unfortunately I don't know how to fix this. Any ideas? > > If the generic PMTU handling in net/ipv4/route.c is adjusting the MTU > for the IPSEC path's route, that would be the problem. > Yes, this is exactly what happens. We use icmp_send() to notify about message size errors even for locally generated packets, this leads to an incorrect pmtu update. Changing this to use ip_local_error() if we have socket context fixes the problem. I'll send a patch for this too. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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