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#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <poll.h>
#include <errno.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <assert.h>
#include "util.h"
#include "sshnc.h"
const char *g_hostkey_hash_preload;
static int writeall(int sock, const char *buffer, size_t length) {
size_t cursor = 0;
while (cursor < length) {
ssize_t nw = write(sock, buffer + cursor, length - cursor);
if (nw < 0) {
if (errno == EINTR) continue;
return -1; // just dump all error conditions together
}
if (nw == 0) return -1; // eof is also an error condition
cursor += nw;
}
return 0;
}
static bool hostkey_checker(const unsigned char *hash, size_t length, void *userdata) {
(void)userdata;
const char* showed = sshnc_print_hash(hash, length);
bool ok = strcmp(showed, g_hostkey_hash_preload) == 0;
if (!ok) {
fprintf(stderr, "Rejecting host key '%s'!\n", showed);
}
return ok;
}
struct thread_data {
const char *server_host;
int server_port;
int client_sock;
};
static void* proxy_thread_entry(void *thread_data_) {
struct thread_data *thread_data = thread_data_;
int client_sock = thread_data->client_sock;
struct sshnc_client *client;
enum sshnc_retval ret = sshnc_connect(
thread_data->server_host, thread_data->server_port, "tomsg", "tomsg",
hostkey_checker, NULL, &client);
if (ret != SSHNC_OK) {
fprintf(stderr, "Could not connect over SSH: %s\n", sshnc_strerror(ret));
return NULL;
}
struct pollfd polls[2];
polls[0] = (struct pollfd){
.fd = sshnc_poll_fd(client),
.events = POLLIN,
};
polls[1] = (struct pollfd){
.fd = client_sock,
.events = POLLIN,
};
while (true) {
int pollret = poll(polls, sizeof polls / sizeof polls[0], -1);
if (pollret < 0) {
perror("poll");
goto cleanup;
}
if (polls[0].revents & (POLLERR | POLLNVAL)) {
fprintf(stderr, "Error reading from SSH socket\n");
goto cleanup;
}
if (polls[1].revents & (POLLERR | POLLNVAL)) {
// Assume downstream has been closed
break;
}
if (polls[0].revents & (POLLIN | POLLHUP)) {
char buffer[4096];
size_t length = 0;
ret = sshnc_maybe_recv(client, sizeof buffer, buffer, &length);
if (ret == SSHNC_OK) {
if (writeall(client_sock, buffer, length) < 0) {
// Error writing back to downstream, let's just close
break;
}
} else if (ret == SSHNC_EOF) {
break;
} else if (ret != SSHNC_AGAIN) {
fprintf(stderr, "Error on SSH recv: %s\n", sshnc_strerror(ret));
goto cleanup;
}
}
if (polls[1].revents & (POLLIN | POLLHUP)) {
char buffer[4096];
ssize_t nr = read(client_sock, buffer, sizeof buffer);
if (nr < 0) {
if (errno == ECONNRESET) break;
perror("Error reading from downstream");
goto cleanup;
}
if (nr == 0) {
break;
}
ret = sshnc_send(client, buffer, nr);
if (ret == SSHNC_EOF) {
break;
} else if (ret != SSHNC_OK) {
fprintf(stderr, "Error on SSH send: %s\n", sshnc_strerror(ret));
goto cleanup;
}
}
}
cleanup:
close(client_sock);
sshnc_close(client);
return NULL;
}
int main(int argc, char **argv) {
const char *server_host = NULL;
int server_port = 2222;
if (argc != 4) {
fprintf(stderr, "Usage: %s <server[:port]> <listen_port> <hostkey_hash_preload>\n", argv[0]);
fprintf(stderr, "If :port is not specified for the backend server, %d is assumed.\n", server_port);
fprintf(stderr, "Will listen for connections to proxy on <listen_port>.\n");
fprintf(stderr, "The hostkey hash should be in the form 'SHA256:base64'.\n");
return 1;
}
if (!parse_host_port(argv[1], &server_host, &server_port)) {
fprintf(stderr, "Cannot parse host:port from argument '%s'\n", argv[1]);
return 1;
}
int bindport = strtol(argv[2], NULL, 10);
if (bindport == 0) {
fprintf(stderr, "Invalid listen port given\n");
return 1;
}
if (memcmp(argv[3], "SHA256:", 7) != 0) {
fprintf(stderr, "Preloaded host key in invalid format\n");
return 1;
}
g_hostkey_hash_preload = argv[3];
int bindsock = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_TCP);
if (bindsock < 0) {
perror("socket(bind)");
return 1;
}
const int yes = 1;
if (setsockopt(bindsock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof yes) < 0) {
fprintf(stderr, "Warning: could not set SO_REUSEADDR\n");
}
struct sockaddr_in bindaddr;
memset(&bindaddr, 0, sizeof bindaddr);
bindaddr.sin_family = AF_INET;
bindaddr.sin_port = htons(bindport);
bindaddr.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(bindsock, (const struct sockaddr*)&bindaddr, sizeof bindaddr) < 0) {
perror("bind");
return 1;
}
if (listen(bindsock, 5) < 0) {
perror("listen");
return 1;
}
pthread_attr_t thread_attr;
assert(pthread_attr_init(&thread_attr) == 0);
assert(pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_DETACHED) == 0);
while (true) {
int sock = accept(bindsock, NULL, NULL);
if (sock < 0) {
perror("accept");
return 1;
}
struct thread_data *data = malloc(sizeof(struct thread_data));
if (!data) { // OOM, reject this connection and try to go on
close(sock);
usleep(500000);
continue;
}
data->server_host = server_host;
data->server_port = server_port;
data->client_sock = sock;
pthread_t thread;
int ret = pthread_create(&thread, &thread_attr, proxy_thread_entry, data);
if (ret < 0) {
// Something happened; reject this connection and try to go on
free(data);
close(sock);
perror("pthread_create");
usleep(500000);
continue;
}
}
}
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