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/*
* NAME: injectaddr.so
*
* SYSOPSIS:
* % gcc -shared -fPIC injectaddr.c -ldl -o injectaddr.so
*
* -- inject 1s delay, then connect to 127.0.0.1:8888
* % LD_PRELOAD=injectaddr.so \
* curl http://d1000.p8888.4127-0-0-1.inject.example.com/
*
*
* This preload library overrides getaddrinfo (3), letting applications specify
* returned IP addresses, ports, and delay. The intended use-case is to
* simulate behavior of complex DNS responses / for testing load balancing
* implementations.
*
* When suffix of the hostname is `.inject.example.com`, the prefix is
* interpreted as commands being passed to the preload library split by dots.
* Accepted commands are:
*
* d<msec> inject delay (specified by milliseconds)
* p<port> return specified port number for the addresses that follow
* 4<addr> return specified IPv4 address
* 6<addr> return specified IPv6 address
*
* IPv4 and v6 addresses use `-` as the separator instead of `.` or `:`.
*/
/*
* Copyright (c) 2021 Kazuho Oku
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#ifdef __linux__
#define _GNU_SOURCE
#endif
#include <arpa/inet.h>
#include <dlfcn.h>
#include <inttypes.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
#define die(msg) dief("injectaddr: " msg "\n")
static void dief(const char *msg)
{
write(2, msg, strlen(msg));
abort();
}
int getaddrinfo(const char *host, const char *serv, const struct addrinfo *hints, struct addrinfo **res)
{
static const char inject_suffix[] = ".inject.example.com";
size_t host_len = strlen(host);
if (host_len < sizeof(inject_suffix) - 1 || strcasecmp(host + host_len - (sizeof(inject_suffix) - 1), inject_suffix) != 0) {
int (*orig)(const char *, const char *, const struct addrinfo *, struct addrinfo **) = dlsym(RTLD_NEXT, "getaddrinfo");
if (orig == NULL)
die("failed to locate original getaddrinfo");
return orig(host, serv, hints, res);
}
int ret = EAI_NONAME;
int sleep_msec = 0;
uint16_t port;
if (sscanf(serv, "%" SCNu16, &port) != 1)
die("invalid serv");
size_t off = 0;
while (off < host_len - (sizeof(inject_suffix) - 1)) {
int cmd = host[off++];
switch (cmd) {
case 'd': /* set delay */
for (; '0' <= host[off] && host[off] <= '9'; ++off)
sleep_msec = sleep_msec * 10 + host[off] - '0';
break;
case 'p': /* override port number */
port = 0;
for (; '0' <= host[off] && host[off] <= '9'; ++off)
port = port * 10 + host[off] - '0';
break;
case '4': /* IPv4 address */
case '6': /* IPv6 address */ {
char addrbuf[5 * 8], *p = addrbuf; /* TODO fix overrun of addrbuf */
for (; host[off] != '.'; ++off)
*p++ = host[off] == '-' ? cmd == '4' ? '.' : ':' : host[off];
*p = '\0';
if (hints->ai_family == AF_UNSPEC || hints->ai_family == (cmd == '4' ? AF_INET : AF_INET6)) {
if (sleep_msec != 0) {
usleep(sleep_msec * 1000);
sleep_msec = 0;
}
*res = malloc(sizeof(**res));
**res = (struct addrinfo){
.ai_flags = 0,
.ai_family = cmd == '4' ? AF_INET : AF_INET6,
.ai_socktype = hints->ai_socktype,
};
if (cmd == '4') {
struct sockaddr_in *sin = malloc(sizeof(*sin));
memset(sin, 0, sizeof(*sin));
sin->sin_family = AF_INET;
if (inet_pton(AF_INET, addrbuf, &sin->sin_addr) != 1)
die("invalid v4 address");
sin->sin_port = htons(port);
(*res)->ai_addr = (struct sockaddr *)sin;
(*res)->ai_addrlen = sizeof(*sin);
} else {
struct sockaddr_in6 *sin6 = malloc(sizeof(*sin6));
memset(sin6, 0, sizeof(*sin6));
sin6->sin6_family = AF_INET6;
if (inet_pton(AF_INET6, addrbuf, &sin6->sin6_addr) != 1)
die("invalid v6 address");
sin6->sin6_port = htons(port);
(*res)->ai_addr = (struct sockaddr *)sin6;
(*res)->ai_addrlen = sizeof(*sin6);
}
res = &(*res)->ai_next;
ret = 0;
}
}
break;
case '.': /* skip . */
break;
default:
die("unexpected command");
break;
}
}
return ret;
}
void freeaddrinfo(struct addrinfo *res)
{
/* TODO implement. Note that Wrapped `getaddrinfo` should convert the original format to our internal, as we have to build
* `addrinfo` ourselves when injecting, without knoweledge of how libc builds the structure. */
}
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