tcp: syncookies: reduce mss table to four values (08629354) · Commits · 戴 / test

net/ipv4/syncookies.c

+11 −11

Original line number	Diff line number	Diff line
		@@ -136,22 +136,22 @@ static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
		}

		/*
		* MSS Values are taken from the 2009 paper
		* 'Measuring TCP Maximum Segment Size' by S. Alcock and R. Nelson:
		* - values 1440 to 1460 accounted for 80% of observed mss values
		* - values outside the 536-1460 range are rare (<0.2%).
		* MSS Values are chosen based on the 2011 paper
		* 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson.
		* Values ..
		* .. lower than 536 are rare (< 0.2%)
		* .. between 537 and 1299 account for less than < 1.5% of observed values
		* .. in the 1300-1349 range account for about 15 to 20% of observed mss values
		* .. exceeding 1460 are very rare (< 0.04%)
		*
		* Table must be sorted.
		* 1460 is the single most frequently announced mss value (30 to 46% depending
		* on monitor location). Table must be sorted.
		*/
		static __u16 const msstab[] = {
		64,
		512,
		536,
		1024,
		1440,
		1300,
		1440, /* 1440, 1452: PPPoE */
		1460,
		4312,
		8960,
		};

		/*

+9 −6

Original line number	Diff line number	Diff line
		@@ -24,15 +24,18 @@
		#define COOKIEBITS 24 /* Upper bits store count */
		#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)

		/* Table must be sorted. */
		/* RFC 2460, Section 8.3:
		* [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
		*
		* Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows
		* using higher values than ipv4 tcp syncookies.
		* The other values are chosen based on ethernet (1500 and 9k MTU), plus
		* one that accounts for common encap (PPPoe) overhead. Table must be sorted.
		*/
		static __u16 const msstab[] = {
		64,
		512,
		536,
		1280 - 60,
		1280 - 60, /* IPV6_MIN_MTU - 60 */
		1480 - 60,
		1500 - 60,
		4460 - 60,
		9000 - 60,
		};