syncookies.c (8c27bd75f04fb9cb70c69c3cfe24f4e6d8e15906) syncookies.c (086293542b991fb88a2e41ae7b4f82ac65a20e1a)
1/*
2 * Syncookies implementation for the Linux kernel
3 *
4 * Copyright (C) 1997 Andi Kleen
5 * Based on ideas by D.J.Bernstein and Eric Schenk.
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License

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131 return (__u32)-1;
132
133 return (cookie -
134 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
135 & COOKIEMASK; /* Leaving the data behind */
136}
137
138/*
1/*
2 * Syncookies implementation for the Linux kernel
3 *
4 * Copyright (C) 1997 Andi Kleen
5 * Based on ideas by D.J.Bernstein and Eric Schenk.
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License

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131 return (__u32)-1;
132
133 return (cookie -
134 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
135 & COOKIEMASK; /* Leaving the data behind */
136}
137
138/*
139 * MSS Values are taken from the 2009 paper
140 * 'Measuring TCP Maximum Segment Size' by S. Alcock and R. Nelson:
141 * - values 1440 to 1460 accounted for 80% of observed mss values
142 * - values outside the 536-1460 range are rare (<0.2%).
139 * MSS Values are chosen based on the 2011 paper
140 * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson.
141 * Values ..
142 * .. lower than 536 are rare (< 0.2%)
143 * .. between 537 and 1299 account for less than < 1.5% of observed values
144 * .. in the 1300-1349 range account for about 15 to 20% of observed mss values
145 * .. exceeding 1460 are very rare (< 0.04%)
143 *
146 *
144 * Table must be sorted.
147 * 1460 is the single most frequently announced mss value (30 to 46% depending
148 * on monitor location). Table must be sorted.
145 */
146static __u16 const msstab[] = {
149 */
150static __u16 const msstab[] = {
147 64,
148 512,
149 536,
151 536,
150 1024,
151 1440,
152 1300,
153 1440, /* 1440, 1452: PPPoE */
152 1460,
154 1460,
153 4312,
154 8960,
155};
156
157/*
158 * Generate a syncookie. mssp points to the mss, which is returned
159 * rounded down to the value encoded in the cookie.
160 */
161u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
162 u16 *mssp)

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156
157/*
158 * Generate a syncookie. mssp points to the mss, which is returned
159 * rounded down to the value encoded in the cookie.
160 */
161u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
162 u16 *mssp)

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