Initial import with working simple server based on libssh examples

.gitignore

@@ -0,0 +1,6 @@
+bastion
+libssh/
+ssh_host_*_key
+test_client.c
+*.[do]
+*.sw[a-p]

GNUmakefile

@@ -0,0 +1,26 @@
+CC=clang
+DEBUG=-g
+CFLAGS= ${DEBUG} -Wall -Werror -Wextra
+
+sources=$(wildcard src/*.c)
+OBJ=$(sources:.c=.o)
+
+all: bastion
+
+bastion: $(OBJ)
+	$(CC) ${DEBUG} -o bastion $(OBJ) -lssh -lpthread -lssh_threads -lutil
+
+clean:
+	$(RM) bastion *.[do] src/*.[do]
+
+%.o: %.c
+	$(CC) -c $(CFLAGS) $*.c -o $*.o
+	$(CC) -MM $(CFLAGS) $*.c > $*.d
+	@mv -f $*.d $*.d.tmp
+	@sed -e 's|.*:|$*.o:|' < $*.d.tmp > $*.d
+	@sed -e 's/.*://' -e 's/\\$$//' < $*.d.tmp | fmt -1 | sed -e 's/^ *//' -e 's/$$/:/' >> $*.d
+	@rm -f $*.d.tmp
+
+valgrind:
+	valgrind --leak-check=full --show-leak-kinds=all --suppressions=$HOME/.valgrind_suppressions ./bastion
+	#valgrind -v --leak-check=full --show-leak-kinds=all --suppressions=$HOME/.valgrind_suppressions --gen-suppressions=yes ./bastion

src/main.c

@@ -0,0 +1,103 @@
+#include <libssh/callbacks.h>
+#include <libssh/server.h>
+//#include <fcntl.h>
+//#include <libutil.h>
+//#include <poll.h>
+//#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+//#include <sys/ioctl.h>
+#include <sys/wait.h>
+//#include <util.h>
+
+#include "session.h"
+
+/* SIGCHLD handler for cleaning up dead children. */
+static void sigchld_handler(int signo) {
+    (void) signo;
+    while (waitpid(-1, NULL, WNOHANG) > 0);
+}
+
+int main()
+{
+    // Set up SIGCHLD handler
+    struct sigaction sa;
+    sa.sa_handler = sigchld_handler;
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESTART | SA_NOCLDSTOP;
+    if (sigaction(SIGCHLD, &sa, NULL) != 0) {
+        fprintf(stderr, "Failed to register SIGCHLD handler\n");
+        return 1;
+    }
+
+    // Initializing ssh context
+    ssh_threads_set_callbacks(ssh_threads_get_pthread());
+    ssh_init();
+
+    // Initializing ssh_bind
+    ssh_bind sshbind = ssh_bind_new();
+    if (sshbind == NULL) {
+        fprintf(stderr, "Error initializing ssh_bind\n");
+        exit(-1);
+    }
+    int port = 2222;
+    ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_BINDPORT, &port);
+    ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_DSAKEY, "ssh_host_dsa_key");
+    ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_RSAKEY, "ssh_host_rsa_key");
+    ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_ECDSAKEY, "ssh_host_ecdsa_key");
+
+    if (ssh_bind_listen(sshbind) < 0) {
+        printf("Error listening to socket: %s\n", ssh_get_error(sshbind));
+        return 1;
+    }
+
+    while (1) {
+        ssh_session session = ssh_new();
+        if (session == NULL) {
+            fprintf(stderr, "Error initializing ssh_session\n");
+            break;
+        }
+        int verbosity = SSH_LOG_PROTOCOL;
+        ssh_options_set(session, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
+
+        // Blocks until there is a new incoming connection
+        if (ssh_bind_accept(sshbind,session) == SSH_OK){
+            switch(fork()) {
+              case 0:
+                /* Remove the SIGCHLD handler inherited from parent. */
+                sa.sa_handler = SIG_DFL;
+                sigaction(SIGCHLD, &sa, NULL);
+                /* Remove socket binding, which allows us to restart the
+                 * parent process, without terminating existing sessions. */
+                ssh_bind_free(sshbind);
+
+                ssh_event event = ssh_event_new();
+                if (event != NULL) {
+                    /* Blocks until the SSH session ends by either
+                     * child process exiting, or client disconnecting. */
+                    handle_session(event, session);
+                    ssh_event_free(event);
+                } else {
+                    fprintf(stderr, "Could not create polling context\n");
+                }
+                ssh_disconnect(session);
+                ssh_free(session);
+
+                exit(0);
+              case -1:
+                fprintf(stderr, "Failed to fork\n");
+            }
+        } else {
+            fprintf(stderr, "Error accepting a connection : %s\n", ssh_get_error(sshbind));
+            exit(1);
+        }
+        /* Since the session has been passed to a child fork, do some cleaning
+         * up at the parent process. */
+        ssh_disconnect(session);
+        ssh_free(session);
+    }
+
+    ssh_bind_free(sshbind);
+    ssh_finalize();
+    return 0;
+}

src/pty.c

@@ -0,0 +1,128 @@
+#include <pty.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <utmp.h>
+
+#include "pty.h"
+
+// callback function for SSH channel PTY request from a client
+int pty_request(ssh_session session, ssh_channel channel,
+                const char *term, int cols, int rows, int py, int px,
+                void *userdata) {
+    struct channel_data_struct *cdata = (struct channel_data_struct *)userdata;
+
+    (void) session;
+    (void) channel;
+    (void) term;
+
+    cdata->winsize->ws_row = rows;
+    cdata->winsize->ws_col = cols;
+    cdata->winsize->ws_xpixel = px;
+    cdata->winsize->ws_ypixel = py;
+
+    if (openpty(&cdata->pty_master, &cdata->pty_slave, NULL, NULL,
+                cdata->winsize) != 0) {
+        fprintf(stderr, "Failed to open pty\n");
+        return SSH_ERROR;
+    }
+    return SSH_OK;
+}
+
+// callback function for SSH channel PTY resize from a client
+int pty_resize(ssh_session session, ssh_channel channel, int cols,
+               int rows, int py, int px, void *userdata) {
+    struct channel_data_struct *cdata = (struct channel_data_struct *)userdata;
+
+    (void) session;
+    (void) channel;
+
+    cdata->winsize->ws_row = rows;
+    cdata->winsize->ws_col = cols;
+    cdata->winsize->ws_xpixel = px;
+    cdata->winsize->ws_ypixel = py;
+
+    if (cdata->pty_master != -1) {
+        return ioctl(cdata->pty_master, TIOCSWINSZ, cdata->winsize);
+    }
+
+    return SSH_ERROR;
+}
+
+int exec_pty(const char *mode, const char *command,
+             struct channel_data_struct *cdata) {
+    switch(cdata->pid = fork()) {
+        case -1:
+            close(cdata->pty_master);
+            close(cdata->pty_slave);
+            fprintf(stderr, "Failed to fork\n");
+            return SSH_ERROR;
+        case 0:
+            close(cdata->pty_master);
+            if (login_tty(cdata->pty_slave) != 0) {
+                exit(1);
+            }
+            execl("/bin/sh", "sh", mode, command, NULL);
+            exit(0);
+        default:
+            close(cdata->pty_slave);
+            /* pty fd is bi-directional */
+            cdata->child_stdout = cdata->child_stdin = cdata->pty_master;
+    }
+    return SSH_OK;
+}
+
+int exec_nopty(const char *command, struct channel_data_struct *cdata) {
+    int in[2], out[2], err[2];
+
+    /* Do the plumbing to be able to talk with the child process. */
+    if (pipe(in) != 0) {
+        goto stdin_failed;
+    }
+    if (pipe(out) != 0) {
+        goto stdout_failed;
+    }
+    if (pipe(err) != 0) {
+        goto stderr_failed;
+    }
+
+    switch(cdata->pid = fork()) {
+        case -1:
+            goto fork_failed;
+        case 0:
+            /* Finish the plumbing in the child process. */
+            close(in[1]);
+            close(out[0]);
+            close(err[0]);
+            dup2(in[0], STDIN_FILENO);
+            dup2(out[1], STDOUT_FILENO);
+            dup2(err[1], STDERR_FILENO);
+            close(in[0]);
+            close(out[1]);
+            close(err[1]);
+            /* exec the requested command. */
+            execl("/bin/sh", "sh", "-c", command, NULL);
+            exit(0);
+    }
+
+    close(in[0]);
+    close(out[1]);
+    close(err[1]);
+
+    cdata->child_stdin = in[1];
+    cdata->child_stdout = out[0];
+    cdata->child_stderr = err[0];
+
+    return SSH_OK;
+
+fork_failed:
+    close(err[0]);
+    close(err[1]);
+stderr_failed:
+    close(out[0]);
+    close(out[1]);
+stdout_failed:
+    close(in[0]);
+    close(in[1]);
+stdin_failed:
+    return SSH_ERROR;
+}

src/pty.h

@@ -0,0 +1,15 @@
+#ifndef _PTY_H_
+#define _PTY_H_
+
+#include "util.h"
+
+int pty_request(ssh_session session, ssh_channel channel,
+                const char *term, int cols, int rows, int py, int px,
+                void *userdata);
+int pty_resize(ssh_session session, ssh_channel channel, int cols,
+               int rows, int py, int px, void *userdata);
+int exec_pty(const char *mode, const char *command,
+             struct channel_data_struct *cdata);
+int exec_nopty(const char *command, struct channel_data_struct *cdata);
+
+#endif

src/session.c

@@ -0,0 +1,271 @@
+#include <libssh/callbacks.h>
+#include <libssh/server.h>
+#include <poll.h>
+#include <pty.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+
+#include "pty.h"
+#include "session.h"
+
+#define USER "julien"
+#define PASS "graou"
+#define BUF_SIZE 1048576
+#define SESSION_END (SSH_CLOSED | SSH_CLOSED_ERROR)
+#define SFTP_SERVER_PATH "/usr/lib/sftp-server"
+
+// callback function for channel data and exceptions
+static int data_function(ssh_session session, ssh_channel channel, void *data,
+                         uint32_t len, int is_stderr, void *userdata) {
+    struct channel_data_struct *cdata = (struct channel_data_struct *) userdata;
+
+    (void) session;
+    (void) channel;
+    (void) is_stderr;
+
+    if (len == 0 || cdata->pid < 1 || kill(cdata->pid, 0) < 0) {
+        return 0;
+    }
+
+    return write(cdata->child_stdin, (char *) data, len);
+}
+
+static int exec_request(ssh_session session, ssh_channel channel,
+                        const char *command, void *userdata) {
+    struct channel_data_struct *cdata = (struct channel_data_struct *) userdata;
+
+
+    (void) session;
+    (void) channel;
+
+    if(cdata->pid > 0) {
+        return SSH_ERROR;
+    }
+
+    if (cdata->pty_master != -1 && cdata->pty_slave != -1) {
+        return exec_pty("-c", command, cdata);
+    }
+    return exec_nopty(command, cdata);
+}
+
+static int shell_request(ssh_session session, ssh_channel channel,
+                         void *userdata) {
+    struct channel_data_struct *cdata = (struct channel_data_struct *) userdata;
+
+    (void) session;
+    (void) channel;
+
+    if(cdata->pid > 0) {
+        return SSH_ERROR;
+    }
+
+    if (cdata->pty_master != -1 && cdata->pty_slave != -1) {
+        return exec_pty("-l", NULL, cdata);
+    }
+    /* Client requested a shell without a pty, let's pretend we allow that */
+    return SSH_OK;
+}
+
+static int subsystem_request(ssh_session session, ssh_channel channel,
+                             const char *subsystem, void *userdata) {
+    /* subsystem requests behave simillarly to exec requests. */
+    if (strcmp(subsystem, "sftp") == 0) {
+        return exec_request(session, channel, SFTP_SERVER_PATH, userdata);
+    }
+    return SSH_ERROR;
+}
+
+static int auth_password(ssh_session session, const char *user,
+                         const char *pass, void *userdata) {
+    struct session_data_struct *sdata = (struct session_data_struct *) userdata;
+
+    (void) session;
+
+    if (strcmp(user, USER) == 0 && strcmp(pass, PASS) == 0) {
+        sdata->authenticated = 1;
+        return SSH_AUTH_SUCCESS;
+    }
+
+    sdata->auth_attempts++;
+    return SSH_AUTH_DENIED;
+}
+
+static ssh_channel channel_open(ssh_session session, void *userdata) {
+    struct session_data_struct *sdata = (struct session_data_struct *) userdata;
+
+    sdata->channel = ssh_channel_new(session);
+    return sdata->channel;
+}
+
+static int process_stdout(socket_t fd, int revents, void *userdata) {
+    char buf[BUF_SIZE];
+    int n = -1;
+    ssh_channel channel = (ssh_channel) userdata;
+
+    if (channel != NULL && (revents & POLLIN) != 0) {
+        n = read(fd, buf, BUF_SIZE);
+        if (n > 0) {
+            ssh_channel_write(channel, buf, n);
+            // TODO implement logging here
+        }
+    }
+
+    return n;
+}
+
+static int process_stderr(socket_t fd, int revents, void *userdata) {
+    char buf[BUF_SIZE];
+    int n = -1;
+    ssh_channel channel = (ssh_channel) userdata;
+
+    if (channel != NULL && (revents & POLLIN) != 0) {
+        n = read(fd, buf, BUF_SIZE);
+        if (n > 0) {
+            ssh_channel_write_stderr(channel, buf, n);
+        }
+    }
+
+    return n;
+}
+
+void handle_session(ssh_event event, ssh_session session) {
+    int n, rc;
+
+    /* Structure for storing the pty size. */
+    struct winsize wsize = {
+        .ws_row = 0,
+        .ws_col = 0,
+        .ws_xpixel = 0,
+        .ws_ypixel = 0
+    };
+
+    /* Our struct holding information about the channel. */
+    struct channel_data_struct cdata = {
+        .pid = 0,
+        .pty_master = -1,
+        .pty_slave = -1,
+        .child_stdin = -1,
+        .child_stdout = -1,
+        .child_stderr = -1,
+        .event = NULL,
+        .winsize = &wsize
+    };
+
+    /* Our struct holding information about the session. */
+    struct session_data_struct sdata = {
+        .channel = NULL,
+        .auth_attempts = 0,
+        .authenticated = 0
+    };
+
+    struct ssh_channel_callbacks_struct channel_cb = {
+        .userdata = &cdata,
+        .channel_pty_request_function = pty_request,
+        .channel_pty_window_change_function = pty_resize,
+        .channel_shell_request_function = shell_request,
+        .channel_exec_request_function = exec_request,
+        .channel_data_function = data_function,
+        .channel_subsystem_request_function = subsystem_request
+    };
+
+    struct ssh_server_callbacks_struct server_cb = {
+        .userdata = &sdata,
+        .auth_password_function = auth_password,
+        .channel_open_request_session_function = channel_open,
+    };
+
+    ssh_callbacks_init(&server_cb);
+    ssh_callbacks_init(&channel_cb);
+
+    ssh_set_server_callbacks(session, &server_cb);
+
+    if (ssh_handle_key_exchange(session) != SSH_OK) {
+        fprintf(stderr, "%s\n", ssh_get_error(session));
+        return;
+    }
+
+    ssh_set_auth_methods(session, SSH_AUTH_METHOD_PASSWORD);
+    ssh_event_add_session(event, session);
+
+    n = 0;
+    while (sdata.authenticated == 0 || sdata.channel == NULL) {
+        /* If the user has used up all attempts, or if he hasn't been able to
+         * authenticate in 10 seconds (n * 100ms), disconnect. */
+        if (sdata.auth_attempts >= 3 || n >= 100) {
+            return;
+        }
+
+        if (ssh_event_dopoll(event, 100) == SSH_ERROR) {
+            fprintf(stderr, "%s\n", ssh_get_error(session));
+            return;
+        }
+        n++;
+    }
+
+    ssh_set_channel_callbacks(sdata.channel, &channel_cb);
+
+    do {
+        /* Poll the main event which takes care of the session, the channel and
+         * even our child process's stdout/stderr (once it's started). */
+        if (ssh_event_dopoll(event, -1) == SSH_ERROR) {
+          ssh_channel_close(sdata.channel);
+        }
+
+        /* If child process's stdout/stderr has been registered with the event,
+         * or the child process hasn't started yet, continue. */
+        if (cdata.event != NULL || cdata.pid == 0) {
+            continue;
+        }
+        /* Executed only once, once the child process starts. */
+        cdata.event = event;
+        /* If stdout valid, add stdout to be monitored by the poll event. */
+        if (cdata.child_stdout != -1) {
+            if (ssh_event_add_fd(event, cdata.child_stdout, POLLIN, process_stdout,
+                                 sdata.channel) != SSH_OK) {
+                fprintf(stderr, "Failed to register stdout to poll context\n");
+                ssh_channel_close(sdata.channel);
+            }
+        }
+
+        /* If stderr valid, add stderr to be monitored by the poll event. */
+        if (cdata.child_stderr != -1){
+            if (ssh_event_add_fd(event, cdata.child_stderr, POLLIN, process_stderr,
+                                 sdata.channel) != SSH_OK) {
+                fprintf(stderr, "Failed to register stderr to poll context\n");
+                ssh_channel_close(sdata.channel);
+            }
+        }
+    } while(ssh_channel_is_open(sdata.channel) &&
+            (cdata.pid == 0 || waitpid(cdata.pid, &rc, WNOHANG) == 0));
+
+    close(cdata.pty_master);
+    close(cdata.child_stdin);
+    close(cdata.child_stdout);
+    close(cdata.child_stderr);
+
+    /* Remove the descriptors from the polling context, since they are now
+     * closed, they will always trigger during the poll calls. */
+    ssh_event_remove_fd(event, cdata.child_stdout);
+    ssh_event_remove_fd(event, cdata.child_stderr);
+
+    /* If the child process exited. */
+    if (kill(cdata.pid, 0) < 0 && WIFEXITED(rc)) {
+        rc = WEXITSTATUS(rc);
+        ssh_channel_request_send_exit_status(sdata.channel, rc);
+    /* If client terminated the channel or the process did not exit nicely,
+     * but only if something has been forked. */
+    } else if (cdata.pid > 0) {
+        kill(cdata.pid, SIGKILL);
+    }
+
+    ssh_channel_send_eof(sdata.channel);
+    ssh_channel_close(sdata.channel);
+
+    /* Wait up to 5 seconds for the client to terminate the session. */
+    for (n = 0; n < 50 && (ssh_get_status(session) & SESSION_END) == 0; n++) {
+        ssh_event_dopoll(event, 100);
+    }
+}

src/session.h

@@ -0,0 +1,10 @@
+#ifndef _SESSION_H_
+#define _SESSION_H_
+
+#include <libssh/libssh.h>
+
+#include "util.h"
+
+void handle_session(ssh_event event, ssh_session session);
+
+#endif

src/util.h

@@ -0,0 +1,32 @@
+#ifndef _UTIL_H_
+#define _UTIL_H_
+
+#include <libssh/libssh.h>
+
+/* A userdata struct for channel. */
+struct channel_data_struct {
+    /* pid of the child process the channel will spawn. */
+    pid_t pid;
+    /* For PTY allocation */
+    socket_t pty_master;
+    socket_t pty_slave;
+    /* For communication with the child process. */
+    socket_t child_stdin;
+    socket_t child_stdout;
+    /* Only used for subsystem and exec requests. */
+    socket_t child_stderr;
+    /* Event which is used to poll the above descriptors. */
+    ssh_event event;
+    /* Terminal size struct. */
+    struct winsize *winsize;
+};
+
+/* A userdata struct for session. */
+struct session_data_struct {
+    /* Pointer to the channel the session will allocate. */
+    ssh_channel channel;
+    int auth_attempts;
+    int authenticated;
+};
+
+#endif