#include <machine/rtems-bsd-kernel-space.h>
/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2008 Michael J. Silbersack.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice unmodified, this list of conditions, and the following
* disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
/*
* IP ID generation is a fascinating topic.
*
* In order to avoid ID collisions during packet reassembly, common sense
* dictates that the period between reuse of IDs be as large as possible.
* This leads to the classic implementation of a system-wide counter, thereby
* ensuring that IDs repeat only once every 2^16 packets.
*
* Subsequent security researchers have pointed out that using a global
* counter makes ID values predictable. This predictability allows traffic
* analysis, idle scanning, and even packet injection in specific cases.
* These results suggest that IP IDs should be as random as possible.
*
* The "searchable queues" algorithm used in this IP ID implementation was
* proposed by Amit Klein. It is a compromise between the above two
* viewpoints that has provable behavior that can be tuned to the user's
* requirements.
*
* The basic concept is that we supplement a standard random number generator
* with a queue of the last L IDs that we have handed out to ensure that all
* IDs have a period of at least L.
*
* To efficiently implement this idea, we keep two data structures: a
* circular array of IDs of size L and a bitstring of 65536 bits.
*
* To start, we ask the RNG for a new ID. A quick index into the bitstring
* is used to determine if this is a recently used value. The process is
* repeated until a value is returned that is not in the bitstring.
*
* Having found a usable ID, we remove the ID stored at the current position
* in the queue from the bitstring and replace it with our new ID. Our new
* ID is then added to the bitstring and the queue pointer is incremented.
*
* The lower limit of 512 was chosen because there doesn't seem to be much
* point to having a smaller value. The upper limit of 32768 was chosen for
* two reasons. First, every step above 32768 decreases the entropy. Taken
* to an extreme, 65533 would offer 1 bit of entropy. Second, the number of
* attempts it takes the algorithm to find an unused ID drastically
* increases, killing performance. The default value of 8192 was chosen
* because it provides a good tradeoff between randomness and non-repetition.
*
* With L=8192, the queue will use 16K of memory. The bitstring always
* uses 8K of memory. No memory is allocated until the use of random ids is
* enabled.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/counter.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/random.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
#include <sys/bitstring.h>
#include <net/vnet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
/*
* By default we generate IP ID only for non-atomic datagrams, as
* suggested by RFC6864. We use per-CPU counter for that, or if
* user wants to, we can turn on random ID generation.
*/
VNET_DEFINE_STATIC(int, ip_rfc6864) = 1;
VNET_DEFINE_STATIC(int, ip_do_randomid) = 0;
#define V_ip_rfc6864 VNET(ip_rfc6864)
#define V_ip_do_randomid VNET(ip_do_randomid)
/*
* Random ID state engine.
*/
static MALLOC_DEFINE(M_IPID, "ipid", "randomized ip id state");
VNET_DEFINE_STATIC(uint16_t *, id_array);
VNET_DEFINE_STATIC(bitstr_t *, id_bits);
VNET_DEFINE_STATIC(int, array_ptr);
VNET_DEFINE_STATIC(int, array_size);
VNET_DEFINE_STATIC(int, random_id_collisions);
VNET_DEFINE_STATIC(int, random_id_total);
VNET_DEFINE_STATIC(struct mtx, ip_id_mtx);
#define V_id_array VNET(id_array)
#define V_id_bits VNET(id_bits)
#define V_array_ptr VNET(array_ptr)
#define V_array_size VNET(array_size)
#define V_random_id_collisions VNET(random_id_collisions)
#define V_random_id_total VNET(random_id_total)
#define V_ip_id_mtx VNET(ip_id_mtx)
/*
* Non-random ID state engine is simply a per-cpu counter.
*/
VNET_DEFINE_STATIC(counter_u64_t, ip_id);
#define V_ip_id VNET(ip_id)
static int sysctl_ip_randomid(SYSCTL_HANDLER_ARGS);
static int sysctl_ip_id_change(SYSCTL_HANDLER_ARGS);
static void ip_initid(int);
static uint16_t ip_randomid(void);
static void ipid_sysinit(void);
static void ipid_sysuninit(void);
SYSCTL_DECL(_net_inet_ip);
SYSCTL_PROC(_net_inet_ip, OID_AUTO, random_id,
CTLTYPE_INT | CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(ip_do_randomid), 0, sysctl_ip_randomid, "IU",
"Assign random ip_id values");
SYSCTL_INT(_net_inet_ip, OID_AUTO, rfc6864, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(ip_rfc6864), 0,
"Use constant IP ID for atomic datagrams");
SYSCTL_PROC(_net_inet_ip, OID_AUTO, random_id_period,
CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_VNET,
&VNET_NAME(array_size), 0, sysctl_ip_id_change, "IU", "IP ID Array size");
SYSCTL_INT(_net_inet_ip, OID_AUTO, random_id_collisions,
CTLFLAG_RD | CTLFLAG_VNET,
&VNET_NAME(random_id_collisions), 0, "Count of IP ID collisions");
SYSCTL_INT(_net_inet_ip, OID_AUTO, random_id_total, CTLFLAG_RD | CTLFLAG_VNET,
&VNET_NAME(random_id_total), 0, "Count of IP IDs created");
static int
sysctl_ip_randomid(SYSCTL_HANDLER_ARGS)
{
int error, new;
new = V_ip_do_randomid;
error = sysctl_handle_int(oidp, &new, 0, req);
if (error || req->newptr == NULL)
return (error);
if (new != 0 && new != 1)
return (EINVAL);
if (new == V_ip_do_randomid)
return (0);
if (new == 1 && V_ip_do_randomid == 0)
ip_initid(8192);
/* We don't free memory when turning random ID off, due to race. */
V_ip_do_randomid = new;
return (0);
}
static int
sysctl_ip_id_change(SYSCTL_HANDLER_ARGS)
{
int error, new;
new = V_array_size;
error = sysctl_handle_int(oidp, &new, 0, req);
if (error == 0 && req->newptr) {
if (new >= 512 && new <= 32768)
ip_initid(new);
else
error = EINVAL;
}
return (error);
}
static void
ip_initid(int new_size)
{
uint16_t *new_array;
bitstr_t *new_bits;
new_array = malloc(new_size * sizeof(uint16_t), M_IPID,
M_WAITOK | M_ZERO);
new_bits = malloc(bitstr_size(65536), M_IPID, M_WAITOK | M_ZERO);
mtx_lock(&V_ip_id_mtx);
if (V_id_array != NULL) {
free(V_id_array, M_IPID);
free(V_id_bits, M_IPID);
}
V_id_array = new_array;
V_id_bits = new_bits;
V_array_size = new_size;
V_array_ptr = 0;
V_random_id_collisions = 0;
V_random_id_total = 0;
mtx_unlock(&V_ip_id_mtx);
}
static uint16_t
ip_randomid(void)
{
uint16_t new_id;
mtx_lock(&V_ip_id_mtx);
/*
* To avoid a conflict with the zeros that the array is initially
* filled with, we never hand out an id of zero.
*/
new_id = 0;
do {
if (new_id != 0)
V_random_id_collisions++;
arc4rand(&new_id, sizeof(new_id), 0);
} while (bit_test(V_id_bits, new_id) || new_id == 0);
bit_clear(V_id_bits, V_id_array[V_array_ptr]);
bit_set(V_id_bits, new_id);
V_id_array[V_array_ptr] = new_id;
V_array_ptr++;
if (V_array_ptr == V_array_size)
V_array_ptr = 0;
V_random_id_total++;
mtx_unlock(&V_ip_id_mtx);
return (new_id);
}
void
ip_fillid(struct ip *ip)
{
/*
* Per RFC6864 Section 4
*
* o Atomic datagrams: (DF==1) && (MF==0) && (frag_offset==0)
* o Non-atomic datagrams: (DF==0) || (MF==1) || (frag_offset>0)
*/
if (V_ip_rfc6864 && (ip->ip_off & htons(IP_DF)) == htons(IP_DF))
ip->ip_id = 0;
else if (V_ip_do_randomid)
ip->ip_id = ip_randomid();
else {
counter_u64_add(V_ip_id, 1);
/*
* There are two issues about this trick, to be kept in mind.
* 1) We can migrate between counter_u64_add() and next
* line, and grab counter from other CPU, resulting in too
* quick ID reuse. This is tolerable in our particular case,
* since probability of such event is much lower then reuse
* of ID due to legitimate overflow, that at modern Internet
* speeds happens all the time.
* 2) We are relying on the fact that counter(9) is based on
* UMA_ZONE_PCPU uma(9) zone. We also take only last
* sixteen bits of a counter, so we don't care about the
* fact that machines with 32-bit word update their counters
* not atomically.
*/
ip->ip_id = htons((*(uint64_t *)zpcpu_get(V_ip_id)) & 0xffff);
}
}
static void
ipid_sysinit(void)
{
int i;
mtx_init(&V_ip_id_mtx, "ip_id_mtx", NULL, MTX_DEF);
V_ip_id = counter_u64_alloc(M_WAITOK);
CPU_FOREACH(i)
arc4rand(zpcpu_get_cpu(V_ip_id, i), sizeof(uint64_t), 0);
}
VNET_SYSINIT(ip_id, SI_SUB_PROTO_DOMAIN, SI_ORDER_ANY, ipid_sysinit, NULL);
static void
ipid_sysuninit(void)
{
if (V_id_array != NULL) {
free(V_id_array, M_IPID);
free(V_id_bits, M_IPID);
}
counter_u64_free(V_ip_id);
mtx_destroy(&V_ip_id_mtx);
}
VNET_SYSUNINIT(ip_id, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD, ipid_sysuninit, NULL);
