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runcmd.c

/*****************************************************************************
* 
* Nagios run command utilities
* 
* License: GPL
* Copyright (c) 2005-2006 Nagios Plugins Development Team
* 
* Description :
* 
* A simple interface to executing programs from other programs, using an
* optimized and safe popen()-like implementation. It is considered safe
* in that no shell needs to be spawned and the environment passed to the
* execve()'d program is essentially empty.
* 
* The code in this file is a derivative of popen.c which in turn was taken
* from "Advanced Programming for the Unix Environment" by W. Richard Stevens.
* 
* Care has been taken to make sure the functions are async-safe. The one
* function which isn't is np_runcmd_init() which it doesn't make sense to
* call twice anyway, so the api as a whole should be considered async-safe.
* 
* 
* 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 3 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, see <http://www.gnu.org/licenses/>.
* 
* 
*****************************************************************************/

#define NAGIOSPLUG_API_C 1

/** includes **/
#include "runcmd.h"
#ifdef HAVE_SYS_WAIT_H
# include <sys/wait.h>
#endif

/** macros **/
#ifndef WEXITSTATUS
# define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8)
#endif

#ifndef WIFEXITED
# define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
#endif

/* 4.3BSD Reno <signal.h> doesn't define SIG_ERR */
#if defined(SIG_IGN) && !defined(SIG_ERR)
# define SIG_ERR ((Sigfunc *)-1)
#endif

/* This variable must be global, since there's no way the caller
 * can forcibly slay a dead or ungainly running program otherwise.
 * Multithreading apps and plugins can initialize it (via NP_RUNCMD_INIT)
 * in an async safe manner PRIOR to calling np_runcmd() for the first time.
 *
 * The check for initialized values is atomic and can
 * occur in any number of threads simultaneously. */
static pid_t *np_pids = NULL;

/* Try sysconf(_SC_OPEN_MAX) first, as it can be higher than OPEN_MAX.
 * If that fails and the macro isn't defined, we fall back to an educated
 * guess. There's no guarantee that our guess is adequate and the program
 * will die with SIGSEGV if it isn't and the upper boundary is breached. */
#ifdef _SC_OPEN_MAX
static long maxfd = 0;
#elif defined(OPEN_MAX)
# define maxfd OPEN_MAX
#else /* sysconf macro unavailable, so guess (may be wildly inaccurate) */
# define maxfd 256
#endif


/** prototypes **/
static int np_runcmd_open(const char *, int *, int *)
      __attribute__((__nonnull__(1, 2, 3)));

static int np_fetch_output(int, output *, int)
      __attribute__((__nonnull__(2)));

static int np_runcmd_close(int);

/* prototype imported from utils.h */
extern void die (int, const char *, ...)
      __attribute__((__noreturn__,__format__(__printf__, 2, 3)));


/* this function is NOT async-safe. It is exported so multithreaded
 * plugins (or other apps) can call it prior to running any commands
 * through this api and thus achieve async-safeness throughout the api */
void np_runcmd_init(void)
{
#ifndef maxfd
      if(!maxfd && (maxfd = sysconf(_SC_OPEN_MAX)) < 0) {
            /* possibly log or emit a warning here, since there's no
             * guarantee that our guess at maxfd will be adequate */
            maxfd = 256;
      }
#endif

      if(!np_pids) np_pids = calloc(maxfd, sizeof(pid_t));
}


/* Start running a command */
static int
np_runcmd_open(const char *cmdstring, int *pfd, int *pfderr)
{
      char *env[2];
      char *cmd = NULL;
      char **argv = NULL;
      char *str;
      int argc;
      size_t cmdlen;
      pid_t pid;
#ifdef RLIMIT_CORE
      struct rlimit limit;
#endif

      int i = 0;

      if(!np_pids) NP_RUNCMD_INIT;

      env[0] = strdup("LC_ALL=C");
      env[1] = '\0';

      /* if no command was passed, return with no error */
      if (cmdstring == NULL)
            return -1;

      /* make copy of command string so strtok() doesn't silently modify it */
      /* (the calling program may want to access it later) */
      cmdlen = strlen(cmdstring);
      if((cmd = malloc(cmdlen + 1)) == NULL) return -1;
      memcpy(cmd, cmdstring, cmdlen);
      cmd[cmdlen] = '\0';

      /* This is not a shell, so we don't handle "???" */
      if (strstr (cmdstring, "\"")) return -1;

      /* allow single quotes, but only if non-whitesapce doesn't occur on both sides */
      if (strstr (cmdstring, " ' ") || strstr (cmdstring, "'''"))
            return -1;

      /* each arg must be whitespace-separated, so args can be a maximum
       * of (len / 2) + 1. We add 1 extra to the mix for NULL termination */
      argc = (cmdlen >> 1) + 2;
      argv = calloc(sizeof(char *), argc);

      if (argv == NULL) {
            printf ("%s\n", _("Could not malloc argv array in popen()"));
            return -1;
      }

      /* get command arguments (stupidly, but fairly quickly) */
      while (cmd) {
            str = cmd;
            str += strspn (str, " \t\r\n"); /* trim any leading whitespace */

            if (strstr (str, "'") == str) {     /* handle SIMPLE quoted strings */
                  str++;
                  if (!strstr (str, "'")) return -1;  /* balanced? */
                  cmd = 1 + strstr (str, "'");
                  str[strcspn (str, "'")] = 0;
            }
            else {
                  if (strpbrk (str, " \t\r\n")) {
                        cmd = 1 + strpbrk (str, " \t\r\n");
                        str[strcspn (str, " \t\r\n")] = 0;
                  }
                  else {
                        cmd = NULL;
                  }
            }

            if (cmd && strlen (cmd) == strspn (cmd, " \t\r\n"))
                  cmd = NULL;

            argv[i++] = str;
      }

      if (pipe(pfd) < 0 || pipe(pfderr) < 0 || (pid = fork()) < 0)
            return -1; /* errno set by the failing function */

      /* child runs exceve() and _exit. */
      if (pid == 0) {
#ifdef      RLIMIT_CORE
            /* the program we execve shouldn't leave core files */
            getrlimit (RLIMIT_CORE, &limit);
            limit.rlim_cur = 0;
            setrlimit (RLIMIT_CORE, &limit);
#endif
            close (pfd[0]);
            if (pfd[1] != STDOUT_FILENO) {
                  dup2 (pfd[1], STDOUT_FILENO);
                  close (pfd[1]);
            }
            close (pfderr[0]);
            if (pfderr[1] != STDERR_FILENO) {
                  dup2 (pfderr[1], STDERR_FILENO);
                  close (pfderr[1]);
            }

            /* close all descriptors in np_pids[]
             * This is executed in a separate address space (pure child),
             * so we don't have to worry about async safety */
            for (i = 0; i < maxfd; i++)
                  if(np_pids[i] > 0)
                        close (i);

            execve (argv[0], argv, env);
            _exit (STATE_UNKNOWN);
      }

      /* parent picks up execution here */
      /* close childs descriptors in our address space */
      close(pfd[1]);
      close(pfderr[1]);

      /* tag our file's entry in the pid-list and return it */
      np_pids[pfd[0]] = pid;

      return pfd[0];
}


static int
np_runcmd_close(int fd)
{
      int status;
      pid_t pid;

      /* make sure this fd was opened by popen() */
      if(fd < 0 || fd > maxfd || !np_pids || (pid = np_pids[fd]) == 0)
            return -1;

      np_pids[fd] = 0;
      if (close (fd) == -1) return -1;

      /* EINTR is ok (sort of), everything else is bad */
      while (waitpid (pid, &status, 0) < 0)
            if (errno != EINTR) return -1;

      /* return child's termination status */
      return (WIFEXITED(status)) ? WEXITSTATUS(status) : -1;
}


void
popen_timeout_alarm_handler (int signo)
{
      size_t i;

      if (signo == SIGALRM)
            puts(_("CRITICAL - Plugin timed out while executing system call\n"));

      if(np_pids) for(i = 0; i < maxfd; i++) {
            if(np_pids[i] != 0) kill(np_pids[i], SIGKILL);
      }

      exit (STATE_CRITICAL);
}


static int
np_fetch_output(int fd, output *op, int flags)
{
      size_t len = 0, i = 0, lineno = 0;
      size_t rsf = 6, ary_size = 0; /* rsf = right shift factor, dec'ed uncond once */
      char *buf = NULL;
      int ret;
      char tmpbuf[4096];

      op->buf = NULL;
      op->buflen = 0;
      while((ret = read(fd, tmpbuf, sizeof(tmpbuf))) > 0) {
            len = (size_t)ret;
            op->buf = realloc(op->buf, op->buflen + len + 1);
            memcpy(op->buf + op->buflen, tmpbuf, len);
            op->buflen += len;
            i++;
      }

      if(ret < 0) {
            printf("read() returned %d: %s\n", ret, strerror(errno));
            return ret;
      }

      /* some plugins may want to keep output unbroken, and some commands
       * will yield no output, so return here for those */
      if(flags & RUNCMD_NO_ARRAYS || !op->buf || !op->buflen)
            return op->buflen;

      /* and some may want both */
      if(flags & RUNCMD_NO_ASSOC) {
            buf = malloc(op->buflen);
            memcpy(buf, op->buf, op->buflen);
      }
      else buf = op->buf;

      op->line = NULL;
      op->lens = NULL;
      i = 0;
      while(i < op->buflen) {
            /* make sure we have enough memory */
            if(lineno >= ary_size) {
                  /* ary_size must never be zero */
                  do {
                        ary_size = op->buflen >> --rsf;
                  } while(!ary_size);

                  op->line = realloc(op->line, ary_size * sizeof(char *));
                  op->lens = realloc(op->lens, ary_size * sizeof(size_t));
            }

            /* set the pointer to the string */
            op->line[lineno] = &buf[i];

            /* hop to next newline or end of buffer */
            while(buf[i] != '\n' && i < op->buflen) i++;
            buf[i] = '\0';

            /* calculate the string length using pointer difference */
            op->lens[lineno] = (size_t)&buf[i] - (size_t)op->line[lineno];

            lineno++;
            i++;
      }

      return lineno;
}


int
np_runcmd(const char *cmd, output *out, output *err, int flags)
{
      int fd, pfd_out[2], pfd_err[2];

      /* initialize the structs */
      if(out) memset(out, 0, sizeof(output));
      if(err) memset(err, 0, sizeof(output));

      if((fd = np_runcmd_open(cmd, pfd_out, pfd_err)) == -1)
            die (STATE_UNKNOWN, _("Could not open pipe: %s\n"), cmd);

      if(out) out->lines = np_fetch_output(pfd_out[0], out, flags);
      if(err) err->lines = np_fetch_output(pfd_err[0], err, flags);

      return np_runcmd_close(fd);
}

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