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From: "Jonathan Lemon" <jonathan.lemon@gmail.com>
To: "Eric Dumazet" <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	"Eric Dumazet" <eric.dumazet@gmail.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Jonathan Looney" <jtl@netflix.com>,
	"Neal Cardwell" <ncardwell@google.com>,
	"Tyler Hicks" <tyhicks@canonical.com>,
	"Yuchung Cheng" <ycheng@google.com>,
	"Bruce Curtis" <brucec@netflix.com>
Subject: Re: [PATCH net 3/4] tcp: add tcp_min_snd_mss sysctl
Date: Mon, 17 Jun 2019 10:15:46 -0700
Message-ID: <DDC9B07B-14FD-41D4-A6F8-725957CEA023@gmail.com> (raw)
In-Reply-To: <20190617170354.37770-4-edumazet@google.com>



On 17 Jun 2019, at 10:03, Eric Dumazet wrote:

> Some TCP peers announce a very small MSS option in their SYN and/or
> SYN/ACK messages.
>
> This forces the stack to send packets with a very high network/cpu
> overhead.
>
> Linux has enforced a minimal value of 48. Since this value includes
> the size of TCP options, and that the options can consume up to 40
> bytes, this means that each segment can include only 8 bytes of payload.
>
> In some cases, it can be useful to increase the minimal value
> to a saner value.
>
> We still let the default to 48 (TCP_MIN_SND_MSS), for compatibility
> reasons.
>
> Note that TCP_MAXSEG socket option enforces a minimal value
> of (TCP_MIN_MSS). David Miller increased this minimal value
> in commit c39508d6f118 ("tcp: Make TCP_MAXSEG minimum more correct.")
> from 64 to 88.
>
> We might in the future merge TCP_MIN_SND_MSS and TCP_MIN_MSS.
>
> CVE-2019-11479 -- tcp mss hardcoded to 48
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Suggested-by: Jonathan Looney <jtl@netflix.com>
> Acked-by: Neal Cardwell <ncardwell@google.com>
> Cc: Yuchung Cheng <ycheng@google.com>
> Cc: Tyler Hicks <tyhicks@canonical.com>
> Cc: Bruce Curtis <brucec@netflix.com>
> Cc: Jonathan Lemon <jonathan.lemon@gmail.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-17 17:03 [PATCH net 0/4] tcp: make sack processing more robust Eric Dumazet
2019-06-17 17:03 ` [PATCH net 1/4] tcp: limit payload size of sacked skbs Eric Dumazet
2019-06-17 17:14   ` Jonathan Lemon
2019-06-17 17:03 ` [PATCH net 2/4] tcp: tcp_fragment() should apply sane memory limits Eric Dumazet
2019-06-17 17:14   ` Jonathan Lemon
2019-06-18  0:18   ` Christoph Paasch
2019-06-18  2:28     ` Eric Dumazet
2019-06-18  3:19       ` Christoph Paasch
2019-06-18  3:44         ` Eric Dumazet
2019-06-18  3:53           ` Christoph Paasch
2019-06-18  4:08             ` Eric Dumazet
2019-07-10 18:23         ` Prout, Andrew - LLSC - MITLL
2019-07-10 18:28           ` Eric Dumazet
2019-07-10 18:53             ` Prout, Andrew - LLSC - MITLL
2019-07-10 19:26               ` Eric Dumazet
2019-07-11  7:28                 ` Christoph Paasch
2019-07-11  9:19                   ` Eric Dumazet
2019-07-11 18:26                     ` Michal Kubecek
2019-07-11 18:50                       ` Eric Dumazet
2019-07-11 10:18                   ` Eric Dumazet
2019-07-11 17:14                 ` Prout, Andrew - LLSC - MITLL
2019-07-11 18:28                   ` Eric Dumazet
2019-07-11 19:04                     ` Jonathan Lemon
2019-07-12  7:05                       ` Eric Dumazet
2019-07-16 15:13                   ` Prout, Andrew - LLSC - MITLL
2019-06-17 17:03 ` [PATCH net 3/4] tcp: add tcp_min_snd_mss sysctl Eric Dumazet
2019-06-17 17:15   ` Jonathan Lemon [this message]
2019-06-17 17:18   ` Tyler Hicks
2019-06-17 17:03 ` [PATCH net 4/4] tcp: enforce tcp_min_snd_mss in tcp_mtu_probing() Eric Dumazet
2019-06-17 17:16   ` Jonathan Lemon
2019-06-17 17:18   ` Tyler Hicks
2019-06-17 17:41 ` [PATCH net 0/4] tcp: make sack processing more robust David Miller

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