From: Paolo Abeni <pabeni@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>,
Mat Martineau <mathew.j.martineau@linux.intel.com>,
netdev@vger.kernel.org, mptcp@lists.01.org
Subject: Re: [MPTCP] Re: [PATCH net-next 09/11] tcp: Check for filled TCP option space before SACK
Date: Mon, 16 Dec 2019 18:28:13 +0100 [thread overview]
Message-ID: <efc70920e3dcdb694ad5791b845f4cf05478b07f.camel@redhat.com> (raw)
In-Reply-To: <d5b3a6ed-fb57-e74d-ef63-ebc4ce49e4b7@gmail.com>
On Mon, 2019-12-16 at 08:55 -0800, Eric Dumazet wrote:
> On 12/16/19 4:52 AM, Paolo Abeni wrote:
> > Thank you for the feedback!
> >
> > Unfortunatelly, the above commit is not enough when MPTCP is enabled,
> > as, without this patch, we can reach the following code:
> >
> > const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
> > opts->num_sack_blocks =
> > min_t(unsigned int, eff_sacks,
> > (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
> > TCPOLEN_SACK_PERBLOCK);
> >
> > with 'size == MAX_TCP_OPTION_SPACE' and num_sack_blocks will be
> > miscalculated. So we need 'fix' but only for MPTCP/when MPTCP is
> > enabled. Still ok for a -net commit?
> >
>
> Does it means MPTCP flows can not use SACK at all ? That would be very bad.
>
> What is the size of MPTCP options ?
MPTCP DSS+ACK+csum is up to 28 bytes, but an MPTCP stream does not need
to attach such option to each packet.
Bare MPTCP ACK are at most 12 bytes, so there is enough room for sack.
The MPTCP specs allow for different opt sizes, because e.g. sequence
numbers can be either 32 or 64 bits. Currently we only implement 64
bits seq.
Paolo
next prev parent reply other threads:[~2019-12-16 17:28 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-13 23:00 [PATCH net-next 00/11] Multipath TCP: Prerequisites Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 01/11] net: Make sock protocol value checks more specific Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 02/11] sock: Make sk_protocol a 16-bit value Mat Martineau
2019-12-13 23:16 ` Eric Dumazet
2019-12-14 0:06 ` Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 03/11] tcp: Define IPPROTO_MPTCP Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 04/11] tcp: Add MPTCP option number Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 05/11] tcp, ulp: Add clone operation to tcp_ulp_ops Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 06/11] mptcp: Add MPTCP to skb extensions Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 07/11] tcp: Prevent coalesce/collapse when skb has MPTCP extensions Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 08/11] tcp: Export TCP functions and ops struct Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 09/11] tcp: Check for filled TCP option space before SACK Mat Martineau
2019-12-13 23:22 ` Eric Dumazet
2019-12-14 0:28 ` Mat Martineau
2019-12-16 12:52 ` [MPTCP] " Paolo Abeni
2019-12-16 16:55 ` Eric Dumazet
2019-12-16 17:28 ` Paolo Abeni [this message]
2019-12-13 23:00 ` [PATCH net-next 10/11] tcp: clean ext on tx recycle Mat Martineau
2019-12-13 23:00 ` [PATCH net-next 11/11] skb: add helpers to allocate ext independently from sk_buff Mat Martineau
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