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Diffstat (limited to 'lib/lwip/lwip/contrib/addons/tcp_isn/tcp_isn.c')
| -rw-r--r-- | lib/lwip/lwip/contrib/addons/tcp_isn/tcp_isn.c | 182 |
1 files changed, 182 insertions, 0 deletions
diff --git a/lib/lwip/lwip/contrib/addons/tcp_isn/tcp_isn.c b/lib/lwip/lwip/contrib/addons/tcp_isn/tcp_isn.c new file mode 100644 index 0000000..c161499 --- /dev/null +++ b/lib/lwip/lwip/contrib/addons/tcp_isn/tcp_isn.c @@ -0,0 +1,182 @@ +/** + * @file + * + * Reference implementation of the TCP ISN algorithm standardized in RFC 6528. + * Produce TCP Initial Sequence Numbers by combining an MD5-generated hash + * based on the new TCP connection's identity and a stable secret, with the + * current time at 4-microsecond granularity. + * + * Specifically, the implementation uses MD5 to compute a hash of the input + * buffer, which contains both the four-tuple of the new TCP connection (local + * and remote IP address and port), as well as a 16-byte secret to make the + * results unpredictable to external parties. The secret must be given at + * initialization time and should ideally remain the same across system + * reboots. To be sure: the spoofing-resistance of the resulting ISN depends + * mainly on the strength of the supplied secret! + * + * The implementation takes 32 bits from the computed hash, and adds to it the + * current time, in 4-microsecond units. The current time is computed from a + * boot time given at initialization, and the current uptime as provided by + * sys_now(). Thus, it assumes that sys_now() returns a time value that is + * relative to the boot time, i.e., that it starts at 0 at system boot, and + * only ever increases monotonically. + * + * For efficiency reasons, a single MD5 input buffer is used, and partially + * filled in at initialization time. Specifically, of this 64-byte buffer, the + * first 36 bytes are used for the four-way TCP tuple data, followed by the + * 16-byte secret, followed by 12-byte zero padding. The 64-byte size of the + * buffer should achieve the best performance for the actual MD5 computation. + * + * Basic usage: + * + * 1. in your lwipopts.h, add the following lines: + * + * #include <lwip/arch.h> + * struct ip_addr; + * u32_t lwip_hook_tcp_isn(const struct ip_addr *local_ip, u16_t local_port, + * const struct ip_addr *remote_ip, u16_t remote_port); + * "#define LWIP_HOOK_TCP_ISN lwip_hook_tcp_isn"; + * + * 2. from your own code, call lwip_init_tcp_isn() at initialization time, with + * appropriate parameters. + */ + +/* + * Copyright (c) 2016 The MINIX 3 Project. + * 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, + * 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. + * 3. The name of the author may not be used to endorse or promote products + * derived from this software without specific prior written permission. + * + * 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. + * + * Author: David van Moolenbroek <david@minix3.org> + */ + +#include "tcp_isn.h" +#include "lwip/ip_addr.h" +#include "lwip/sys.h" +#include <string.h> + +#ifdef LWIP_HOOK_TCP_ISN + +/* pull in md5 of ppp? */ +#include "netif/ppp/ppp_opts.h" +#if !PPP_SUPPORT || (!LWIP_USE_EXTERNAL_POLARSSL && !LWIP_USE_EXTERNAL_MBEDTLS) +#undef LWIP_INCLUDED_POLARSSL_MD5 +#define LWIP_INCLUDED_POLARSSL_MD5 1 +#include "netif/ppp/polarssl/md5.h" +#endif + +static u8_t input[64]; +static u32_t base_time; + +/** + * Initialize the TCP ISN module, with the boot time and a secret. + * + * @param boot_time Wall clock boot time of the system, in seconds. + * @param secret_16_bytes A 16-byte secret used to randomize the TCP ISNs. + */ +void +lwip_init_tcp_isn(u32_t boot_time, const u8_t *secret_16_bytes) +{ + /* Initialize the input buffer with the secret and trailing zeroes. */ + memset(input, 0, sizeof(input)); + + MEMCPY(&input[36], secret_16_bytes, 16); + + /* Save the boot time in 4-us units. Overflow is no problem here. */ + base_time = boot_time * 250000; +} + +/** + * Hook to generate an Initial Sequence Number (ISN) for a new TCP connection. + * + * @param local_ip The local IP address. + * @param local_port The local port number, in host-byte order. + * @param remote_ip The remote IP address. + * @param remote_port The remote port number, in host-byte order. + * @return The ISN to use for the new TCP connection. + */ +u32_t +lwip_hook_tcp_isn(const ip_addr_t *local_ip, u16_t local_port, + const ip_addr_t *remote_ip, u16_t remote_port) +{ + md5_context ctx; + u8_t output[16]; + u32_t isn; + +#if LWIP_IPV4 && LWIP_IPV6 + if (IP_IS_V6(local_ip)) +#endif /* LWIP_IPV4 && LWIP_IPV6 */ +#if LWIP_IPV6 + { + const ip6_addr_t *local_ip6, *remote_ip6; + + local_ip6 = ip_2_ip6(local_ip); + remote_ip6 = ip_2_ip6(remote_ip); + + SMEMCPY(&input[0], &local_ip6->addr, 16); + SMEMCPY(&input[16], &remote_ip6->addr, 16); + } +#endif /* LWIP_IPV6 */ +#if LWIP_IPV4 && LWIP_IPV6 + else +#endif /* LWIP_IPV4 && LWIP_IPV6 */ +#if LWIP_IPV4 + { + const ip4_addr_t *local_ip4, *remote_ip4; + + local_ip4 = ip_2_ip4(local_ip); + remote_ip4 = ip_2_ip4(remote_ip); + + /* Represent IPv4 addresses as IPv4-mapped IPv6 addresses, to ensure that + * the IPv4 and IPv6 address spaces are completely disjoint. */ + memset(&input[0], 0, 10); + input[10] = 0xff; + input[11] = 0xff; + SMEMCPY(&input[12], &local_ip4->addr, 4); + memset(&input[16], 0, 10); + input[26] = 0xff; + input[27] = 0xff; + SMEMCPY(&input[28], &remote_ip4->addr, 4); + } +#endif /* LWIP_IPV4 */ + + input[32] = (u8_t)(local_port >> 8); + input[33] = (u8_t)(local_port & 0xff); + input[34] = (u8_t)(remote_port >> 8); + input[35] = (u8_t)(remote_port & 0xff); + + /* The secret and padding are already filled in. */ + + /* Generate the hash, using MD5. */ + md5_starts(&ctx); + md5_update(&ctx, input, sizeof(input)); + md5_finish(&ctx, output); + + /* Arbitrarily take the first 32 bits from the generated hash. */ + MEMCPY(&isn, output, sizeof(isn)); + + /* Add the current time in 4-microsecond units. */ + return isn + base_time + sys_now() * 250; +} + +#endif /* LWIP_HOOK_TCP_ISN */ |