qubes-linux-utils/qrexec-lib/exec.c

/*
 * The Qubes OS Project, http://www.qubes-os.org
 *
 * Copyright (C) 2010  Rafal Wojtczuk  <rafal@invisiblethingslab.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * 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.
 *
 */

#include <sys/socket.h>
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include "qrexec.h"
#include "libqrexec-utils.h"

static do_exec_t *exec_func = NULL;
void register_exec_func(do_exec_t *func) {
    exec_func = func;
}

void exec_qubes_rpc_if_requested(char *prog, char *const envp[]) {
    /* avoid calling qubes-rpc-multiplexer through shell */
    if (strncmp(prog, RPC_REQUEST_COMMAND, RPC_REQUEST_COMMAND_LEN) == 0) {
        char *tok;
        char *argv[16]; // right now 6 are used, but allow future extensions
        size_t i = 0;

        tok=strtok(prog, " ");
        do {
            if (i >= sizeof(argv)/sizeof(argv[0])-1) {
                fprintf(stderr, "To many arguments to %s\n", RPC_REQUEST_COMMAND);
                exit(1);
            }
            argv[i++] = tok;
        } while ((tok=strtok(NULL, " ")));
        argv[i] = NULL;
        argv[0] = QUBES_RPC_MULTIPLEXER_PATH;
        execve(QUBES_RPC_MULTIPLEXER_PATH, argv, envp);
        perror("exec qubes-rpc-multiplexer");
        exit(1);
    }
}

void fix_fds(int fdin, int fdout, int fderr)
{
    int i;
    for (i = 0; i < 256; i++)
        if (i != fdin && i != fdout && i != fderr)
            close(i);
    dup2(fdin, 0);
    dup2(fdout, 1);
    dup2(fderr, 2);
    close(fdin);
    close(fdout);
    if (fderr != 2)
        close(fderr);
}

void do_fork_exec(const char *cmdline, int *pid, int *stdin_fd, int *stdout_fd,
        int *stderr_fd)
{
    int inpipe[2], outpipe[2], errpipe[2];

    if (socketpair(AF_UNIX, SOCK_STREAM, 0, inpipe) || 
            socketpair(AF_UNIX, SOCK_STREAM, 0, outpipe) || 
            (stderr_fd && socketpair(AF_UNIX, SOCK_STREAM, 0, errpipe))) {
        perror("socketpair");
        exit(1);
    }
    switch (*pid = fork()) {
        case -1:
            perror("fork");
            exit(-1);
        case 0:
            if (stderr_fd) {
                fix_fds(inpipe[0], outpipe[1], errpipe[1]);
            } else
                fix_fds(inpipe[0], outpipe[1], 2);

            if (exec_func != NULL)
                exec_func((char*)cmdline);
            exit(-1);
        default:;
    }
    close(inpipe[0]);
    close(outpipe[1]);
    *stdin_fd = inpipe[1];
    *stdout_fd = outpipe[0];
    if (stderr_fd) {
        close(errpipe[1]);
        *stderr_fd = errpipe[0];
    }
}