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import of dnsmasq-2.34.tar.gz
This commit is contained in:
Simon Kelley
330
src/helper.c
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330
src/helper.c
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/* dnsmasq is Copyright (c) 2000-2006 Simon Kelley
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 dated June, 1991.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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*/
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#include "dnsmasq.h"
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/* This file has code to fork a helper process which recieves data via a pipe
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shared with the main process and which is responsible for calling a script when
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DHCP leases change.
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The helper process is forked before the main process drops root, so it retains root
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privs to pass on to the script. For this reason it tries to be paranoid about
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data received from the main process, in case that has been compromised. We don't
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want the helper to give an attacker root. In particular, the script to be run is
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not settable via the pipe, once the fork has taken place it is not alterable by the
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main process.
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*/
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struct script_data
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{
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unsigned char action, hwaddr_len, hwaddr_type;
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unsigned char clid_len, hostname_len, uclass_len, vclass_len;
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struct in_addr addr;
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#ifdef HAVE_BROKEN_RTC
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unsigned int length;
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#else
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time_t expires;
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#endif
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unsigned char hwaddr[DHCP_CHADDR_MAX];
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};
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static struct script_data *buf;
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static size_t bytes_in_buf, buf_size;
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int create_helper(struct daemon *daemon)
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{
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pid_t pid;
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int i, pipefd[2];
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struct sigaction sigact;
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buf = NULL;
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buf_size = bytes_in_buf = 0;
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if (!daemon->dhcp || !daemon->lease_change_command)
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return -1;
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/* create the pipe through which the main program sends us commands,
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then fork our process. */
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if (pipe(pipefd) == -1 || !fix_fd(pipefd[1]) || (pid = fork()) == -1)
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return -1;
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if (pid != 0)
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{
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close(pipefd[0]); /* close reader side */
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return pipefd[1];
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}
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/* ignore SIGTERM, so that we can clean up when the main process gets hit */
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sigact.sa_handler = SIG_IGN;
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sigact.sa_flags = 0;
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sigemptyset(&sigact.sa_mask);
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sigaction(SIGTERM, &sigact, NULL);
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/* close all the sockets etc, we don't need them here */
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for (i = 0; i < 64; i++)
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if (i != STDOUT_FILENO && i != STDERR_FILENO &&
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i != STDIN_FILENO && i != pipefd[0])
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close(i);
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/* we open our own log connection. */
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log_start(daemon);
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/* don't give our end of the pipe to our children */
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if ((i = fcntl(pipefd[0], F_GETFD)) != -1)
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fcntl(pipefd[0], F_SETFD, i | FD_CLOEXEC);
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/* loop here */
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while(1)
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{
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struct script_data data;
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char *p, *action_str, *hostname = NULL;
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unsigned char *buf = (unsigned char *)daemon->namebuff;
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/* we read zero bytes when pipe closed: this is our signal to exit */
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if (!read_write(pipefd[0], (unsigned char *)&data, sizeof(data), 1))
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_exit(0);
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if (data.action == ACTION_DEL)
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action_str = "del";
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else if (data.action == ACTION_ADD)
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action_str = "add";
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else if (data.action == ACTION_OLD || data.action == ACTION_OLD_HOSTNAME)
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action_str = "old";
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else
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continue;
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/* stringify MAC into dhcp_buff */
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p = daemon->dhcp_buff;
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if (data.hwaddr_type != ARPHRD_ETHER || data.hwaddr_len == 0)
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p += sprintf(p, "%.2x-", data.hwaddr_type);
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for (i = 0; (i < data.hwaddr_len) && (i < DHCP_CHADDR_MAX); i++)
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{
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p += sprintf(p, "%.2x", data.hwaddr[i]);
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if (i != data.hwaddr_len - 1)
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p += sprintf(p, ":");
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}
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/* and CLID into packet */
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if (!read_write(pipefd[0], buf, data.clid_len, 1))
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continue;
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for (p = daemon->packet, i = 0; i < data.clid_len; i++)
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{
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p += sprintf(p, "%.2x", buf[i]);
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if (i != data.clid_len - 1)
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p += sprintf(p, ":");
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}
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/* and expiry or length into dhcp_buff2 */
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#ifdef HAVE_BROKEN_RTC
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sprintf(daemon->dhcp_buff2, "%u ", data.length);
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#else
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sprintf(daemon->dhcp_buff2, "%lu ", (unsigned long)data.expires);
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#endif
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if (!read_write(pipefd[0], buf, data.hostname_len + data.uclass_len + data.vclass_len, 1))
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continue;
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if ((pid = fork()) == -1)
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continue;
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/* wait for child to complete */
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if (pid != 0)
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{
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int status;
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waitpid(pid, &status, 0);
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if (WIFSIGNALED(status))
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syslog(LOG_WARNING, _("child process killed by signal %d"), WTERMSIG(status));
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else if (WIFEXITED(status) && WEXITSTATUS(status) != 0)
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syslog(LOG_WARNING, _("child process exited with status %d"), WEXITSTATUS(status));
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continue;
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}
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if (data.clid_len != 0)
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setenv("DNSMASQ_CLIENT_ID", daemon->packet, 1);
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else
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unsetenv("DNSMASQ_CLIENT_ID");
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#ifdef HAVE_BROKEN_RTC
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setenv("DNSMASQ_LEASE_LENGTH", daemon->dhcp_buff2, 1);
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unsetenv("DNSMASQ_LEASE_EXPIRES");
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#else
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setenv("DNSMASQ_LEASE_EXPIRES", daemon->dhcp_buff2, 1);
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unsetenv("DNSMASQ_LEASE_LENGTH");
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#endif
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if (data.vclass_len != 0)
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{
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buf[data.vclass_len - 1] = 0; /* don't trust zero-term */
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/* cannot have = chars in env - truncate if found . */
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if ((p = strchr((char *)buf, '=')))
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*p = 0;
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setenv("DNSMASQ_VENDOR_CLASS", (char *)buf, 1);
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buf += data.vclass_len;
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}
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else
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unsetenv("DNSMASQ_VENDOR_CLASS");
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if (data.uclass_len != 0)
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{
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unsigned char *end = buf + data.uclass_len;
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buf[data.uclass_len - 1] = 0; /* don't trust zero-term */
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for (i = 0; buf < end;)
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{
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size_t len = strlen((char *)buf) + 1;
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if ((p = strchr((char *)buf, '=')))
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*p = 0;
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if (strlen((char *)buf) != 0)
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{
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sprintf(daemon->dhcp_buff2, "DNSMASQ_USER_CLASS%i", i++);
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setenv(daemon->dhcp_buff2, (char *)buf, 1);
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}
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buf += len;
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}
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}
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if (data.hostname_len != 0)
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{
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hostname = (char *)buf;
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hostname[data.hostname_len - 1] = 0;
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canonicalise(hostname);
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}
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if (data.action == ACTION_OLD_HOSTNAME && hostname)
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{
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setenv("DNSMASQ_OLD_HOSTNAME", hostname, 1);
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hostname = NULL;
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}
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else
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unsetenv("DNSMASQ_OLD_HOSTNAME");
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p = strrchr(daemon->lease_change_command, '/');
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execl(daemon->lease_change_command,
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p ? p+1 : daemon->lease_change_command,
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action_str, daemon->dhcp_buff, inet_ntoa(data.addr), hostname, (char*)NULL);
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/* log socket should still be open, right? */
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syslog(LOG_ERR, _("failed to execute %s: %m"),
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daemon->lease_change_command);
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_exit(0);
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}
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}
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/* pack up lease data into a buffer */
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void queue_script(struct daemon *daemon, int action, struct dhcp_lease *lease, char *hostname)
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{
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unsigned char *p;
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size_t size;
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unsigned int hostname_len = 0, clid_len = 0, vclass_len = 0, uclass_len = 0;
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/* no script */
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if (daemon->helperfd == -1)
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return;
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if (action == ACTION_ADD)
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{
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if (lease->vendorclass)
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vclass_len = lease->vendorclass_len;
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if (lease->userclass)
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uclass_len = lease->userclass_len;
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}
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if (lease->clid)
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clid_len = lease->clid_len;
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if (hostname)
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hostname_len = strlen(hostname) + 1;
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size = sizeof(struct script_data) + clid_len + vclass_len + uclass_len + hostname_len;
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if (size > buf_size)
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{
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struct script_data *new;
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/* start with resonable size, will almost never need extending. */
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if (size < sizeof(struct script_data) + 200)
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size = sizeof(struct script_data) + 200;
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if (!(new = malloc(size)))
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return;
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if (buf)
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free(buf);
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buf = new;
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buf_size = size;
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}
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buf->action = action;
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buf->hwaddr_len = lease->hwaddr_len;
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buf->hwaddr_type = lease->hwaddr_type;
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buf->clid_len = clid_len;
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buf->vclass_len = vclass_len;
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buf->uclass_len = uclass_len;
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buf->hostname_len = hostname_len;
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buf->addr = lease->addr;
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memcpy(buf->hwaddr, lease->hwaddr, lease->hwaddr_len);
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#ifdef HAVE_BROKEN_RTC
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buf->length = lease->length;
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#else
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buf->expires = lease->expires;
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#endif
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p = (unsigned char *)(buf+1);
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if (buf->clid_len != 0)
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{
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memcpy(p, lease->clid, clid_len);
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p += clid_len;
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}
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if (buf->vclass_len != 0)
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{
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memcpy(p, lease->vendorclass, vclass_len);
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p += vclass_len;
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}
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if (buf->uclass_len != 0)
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{
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memcpy(p, lease->userclass, uclass_len);
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p += uclass_len;
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}
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if (buf->hostname_len != 0)
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{
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memcpy(p, hostname, hostname_len);
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p += hostname_len;
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}
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bytes_in_buf = p - (unsigned char *)buf;
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}
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int helper_buf_empty(void)
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{
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return bytes_in_buf == 0;
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}
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void helper_write(struct daemon *daemon)
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{
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ssize_t rc;
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if (bytes_in_buf == 0)
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return;
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if ((rc = write(daemon->helperfd, buf, bytes_in_buf)) != -1)
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{
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if (bytes_in_buf != (size_t)rc)
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memmove(buf, buf + rc, bytes_in_buf - rc);
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bytes_in_buf -= rc;
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}
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else
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{
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if (errno == EAGAIN || errno == EINTR)
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return;
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bytes_in_buf = 0;
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}
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}
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