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/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2002-2021 OpenVPN Inc <sales@openvpn.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/*
* Test protocol robustness by simulating dropped packets and
* network outages when the --gremlin option is used.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#elif defined(_MSC_VER)
#include "config-msvc.h"
#endif
#include "syshead.h"
#ifdef ENABLE_DEBUG
#include "error.h"
#include "common.h"
#include "crypto.h"
#include "misc.h"
#include "otime.h"
#include "gremlin.h"
#include "memdbg.h"
/*
* Parameters for packet corruption and droppage.
* Each parameter has 4 possible levels, 0 = disabled,
* while 1, 2, and 3 are enumerated in the below arrays.
* The parameter is a 2-bit field within the --gremlin
* parameter.
*/
/*
* Probability that we will drop a packet is 1 / n
*/
static const int drop_freq[] = { 500, 100, 50 };
/*
* Probability that we will corrupt a packet is 1 / n
*/
static const int corrupt_freq[] = { 500, 100, 50 };
/*
* When network goes up, it will be up for between
* UP_LOW and UP_HIGH seconds.
*/
static const int up_low[] = { 60, 10, 5 };
static const int up_high[] = { 600, 60, 10 };
/*
* When network goes down, it will be down for between
* DOWN_LOW and DOWN_HIGH seconds.
*/
static const int down_low[] = { 5, 10, 10 };
static const int down_high[] = { 10, 60, 120 };
/*
* Packet flood levels:
* { number of packets, packet size }
*/
static const struct packet_flood_parms packet_flood_data[] =
{{10, 100}, {10, 1500}, {100, 1500}};
struct packet_flood_parms
get_packet_flood_parms(int level)
{
ASSERT(level > 0 && level < 4);
return packet_flood_data [level - 1];
}
/*
* Return true with probability 1/n
*/
static bool
flip(int n)
{
return (get_random() % n) == 0;
}
/*
* Return uniformly distributed random number between
* low and high.
*/
static int
roll(int low, int high)
{
int ret;
ASSERT(low <= high);
ret = low + (get_random() % (high - low + 1));
ASSERT(ret >= low && ret <= high);
return ret;
}
static bool initialized; /* GLOBAL */
static bool up; /* GLOBAL */
static time_t next; /* GLOBAL */
/*
* Return false if we should drop a packet.
*/
bool
ask_gremlin(int flags)
{
const int up_down_level = GREMLIN_UP_DOWN_LEVEL(flags);
const int drop_level = GREMLIN_DROP_LEVEL(flags);
if (!initialized)
{
initialized = true;
if (up_down_level)
{
up = false;
}
else
{
up = true;
}
next = now;
}
if (up_down_level) /* change up/down state? */
{
if (now >= next)
{
int delta;
if (up)
{
delta = roll(down_low[up_down_level-1], down_high[up_down_level-1]);
up = false;
}
else
{
delta = roll(up_low[up_down_level-1], up_high[up_down_level-1]);
up = true;
}
msg(D_GREMLIN,
"GREMLIN: CONNECTION GOING %s FOR %d SECONDS",
(up ? "UP" : "DOWN"),
delta);
next = now + delta;
}
}
if (drop_level)
{
if (up && flip(drop_freq[drop_level-1]))
{
dmsg(D_GREMLIN_VERBOSE, "GREMLIN: Random packet drop");
return false;
}
}
return up;
}
/*
* Possibly corrupt a packet.
*/
void
corrupt_gremlin(struct buffer *buf, int flags)
{
const int corrupt_level = GREMLIN_CORRUPT_LEVEL(flags);
if (corrupt_level)
{
if (flip(corrupt_freq[corrupt_level-1]))
{
do
{
if (buf->len > 0)
{
uint8_t r = roll(0, 255);
int method = roll(0, 5);
switch (method)
{
case 0: /* corrupt the first byte */
*BPTR(buf) = r;
break;
case 1: /* corrupt the last byte */
*(BPTR(buf) + buf->len - 1) = r;
break;
case 2: /* corrupt a random byte */
*(BPTR(buf) + roll(0, buf->len - 1)) = r;
break;
case 3: /* append a random byte */
buf_write(buf, &r, 1);
break;
case 4: /* reduce length by 1 */
--buf->len;
break;
case 5: /* reduce length by a random amount */
buf->len -= roll(0, buf->len - 1);
break;
}
dmsg(D_GREMLIN_VERBOSE, "GREMLIN: Packet Corruption, method=%d", method);
}
else
{
break;
}
} while (flip(2)); /* a 50% chance we will corrupt again */
}
}
}
#else /* ifdef ENABLE_DEBUG */
static void
dummy(void)
{
}
#endif /* ifdef ENABLE_DEBUG */
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