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TCPCT part 1d: define TCP cookie option, extend existing struct's

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Data structures are carefully composed to require minimal additions.
For example, the struct tcp_options_received cookie_plus variable fits
between existing 16-bit and 8-bit variables, requiring no additional
space (taking alignment into consideration).  There are no additions to
tcp_request_sock, and only 1 pointer in tcp_sock.

This is a significantly revised implementation of an earlier (year-old)
patch that no longer applies cleanly, with permission of the original
author (Adam Langley):

    http://thread.gmane.org/gmane.linux.network/102586

The principle difference is using a TCP option to carry the cookie nonce,
instead of a user configured offset in the data.  This is more flexible and
less subject to user configuration error.  Such a cookie option has been
suggested for many years, and is also useful without SYN data, allowing
several related concepts to use the same extension option.

    "Re: SYN floods (was: does history repeat itself?)", September 9, 1996.
    http://www.merit.net/mail.archives/nanog/1996-09/msg00235.html

    "Re: what a new TCP header might look like", May 12, 1998.
    ftp://ftp.isi.edu/end2end/end2end-interest-1998.mail

These functions will also be used in subsequent patches that implement
additional features.

Requires:
   TCPCT part 1a: add request_values parameter for sending SYNACK
   TCPCT part 1b: generate Responder Cookie secret
   TCPCT part 1c: sysctl_tcp_cookie_size, socket option TCP_COOKIE_TRANSACTIONS

Signed-off-by: William.Allen.Simpson@gmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
William Allen Simpson
2009-12-02 18:17:05 +00:00
committed by David S. Miller
parent 519855c508
commit 435cf559f0
5 changed files with 177 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

83
include/net/tcp.h
View File

@@ -30,6 +30,7 @@
#include <linux/dmaengine.h>
#include <linux/crypto.h>
#include <linux/cryptohash.h>
#include <linux/kref.h>
#include <net/inet_connection_sock.h>
#include <net/inet_timewait_sock.h>
@@ -164,6 +165,7 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
#define TCPOPT_SACK 5 /* SACK Block */
#define TCPOPT_TIMESTAMP 8 /* Better RTT estimations/PAWS */
#define TCPOPT_MD5SIG 19 /* MD5 Signature (RFC2385) */
#define TCPOPT_COOKIE 253 /* Cookie extension (experimental) */
/*
* TCP option lengths
@@ -174,6 +176,10 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
#define TCPOLEN_SACK_PERM 2
#define TCPOLEN_TIMESTAMP 10
#define TCPOLEN_MD5SIG 18
#define TCPOLEN_COOKIE_BASE 2 /* Cookie-less header extension */
#define TCPOLEN_COOKIE_PAIR 3 /* Cookie pair header extension */
#define TCPOLEN_COOKIE_MIN (TCPOLEN_COOKIE_BASE+TCP_COOKIE_MIN)
#define TCPOLEN_COOKIE_MAX (TCPOLEN_COOKIE_BASE+TCP_COOKIE_MAX)
/* But this is what stacks really send out. */
#define TCPOLEN_TSTAMP_ALIGNED 12
@@ -1482,6 +1488,83 @@ struct tcp_request_sock_ops {
extern int tcp_cookie_generator(u32 *bakery);
/**
* struct tcp_cookie_values - each socket needs extra space for the
* cookies, together with (optional) space for any SYN data.
*
* A tcp_sock contains a pointer to the current value, and this is
* cloned to the tcp_timewait_sock.
*
* @cookie_pair: variable data from the option exchange.
*
* @cookie_desired: user specified tcpct_cookie_desired. Zero
* indicates default (sysctl_tcp_cookie_size).
* After cookie sent, remembers size of cookie.
* Range 0, TCP_COOKIE_MIN to TCP_COOKIE_MAX.
*
* @s_data_desired: user specified tcpct_s_data_desired. When the
* constant payload is specified (@s_data_constant),
* holds its length instead.
* Range 0 to TCP_MSS_DESIRED.
*
* @s_data_payload: constant data that is to be included in the
* payload of SYN or SYNACK segments when the
* cookie option is present.
*/
struct tcp_cookie_values {
struct kref kref;
u8 cookie_pair[TCP_COOKIE_PAIR_SIZE];
u8 cookie_pair_size;
u8 cookie_desired;
u16 s_data_desired:11,
s_data_constant:1,
s_data_in:1,
s_data_out:1,
s_data_unused:2;
u8 s_data_payload[0];
};
static inline void tcp_cookie_values_release(struct kref *kref)
{
kfree(container_of(kref, struct tcp_cookie_values, kref));
}
/* The length of constant payload data. Note that s_data_desired is
* overloaded, depending on s_data_constant: either the length of constant
* data (returned here) or the limit on variable data.
*/
static inline int tcp_s_data_size(const struct tcp_sock *tp)
{
return (tp->cookie_values != NULL && tp->cookie_values->s_data_constant)
? tp->cookie_values->s_data_desired
: 0;
}
/**
* struct tcp_extend_values - tcp_ipv?.c to tcp_output.c workspace.
*
* As tcp_request_sock has already been extended in other places, the
* only remaining method is to pass stack values along as function
* parameters. These parameters are not needed after sending SYNACK.
*
* @cookie_bakery: cryptographic secret and message workspace.
*
* @cookie_plus: bytes in authenticator/cookie option, copied from
* struct tcp_options_received (above).
*/
struct tcp_extend_values {
struct request_values rv;
u32 cookie_bakery[COOKIE_WORKSPACE_WORDS];
u8 cookie_plus:6,
cookie_out_never:1,
cookie_in_always:1;
};
static inline struct tcp_extend_values *tcp_xv(struct request_values *rvp)
{
return (struct tcp_extend_values *)rvp;
}
extern void tcp_v4_init(void);
extern void tcp_init(void);