234 lines
6.1 KiB
C
234 lines
6.1 KiB
C
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/*
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* Copyright (c) 1993 Eric P. Allman
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* Copyright (c) 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)smrsh.c 8.4 (Berkeley) 11/11/95";
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#endif /* not lint */
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/*
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** SMRSH -- sendmail restricted shell
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**
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** This is a patch to get around the prog mailer bugs in most
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** versions of sendmail.
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**
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** Use this in place of /bin/sh in the "prog" mailer definition
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** in your sendmail.cf file. You then create CMDDIR (owned by
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** root, mode 755) and put links to any programs you want
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** available to prog mailers in that directory. This should
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** include things like "vacation" and "procmail", but not "sed"
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** or "sh".
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**
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** Leading pathnames are stripped from program names so that
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** existing .forward files that reference things like
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** "/usr/ucb/vacation" will continue to work.
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**
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** The following characters are completely illegal:
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** < > | ^ ; & $ ` ( ) \n \r
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** This is more restrictive than strictly necessary.
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**
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** To use this, edit /etc/sendmail.cf, search for ^Mprog, and
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** change P=/bin/sh to P=/usr/local/etc/smrsh, where this compiled
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** binary is installed /usr/local/etc/smrsh.
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**
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** This can be used on any version of sendmail.
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**
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** In loving memory of RTM. 11/02/93.
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*/
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#include <unistd.h>
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#include <stdio.h>
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#include <sys/file.h>
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#include <string.h>
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#include <ctype.h>
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#ifdef EX_OK
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# undef EX_OK
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#endif
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#include <sysexits.h>
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#include <syslog.h>
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/* directory in which all commands must reside */
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#ifndef CMDDIR
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# define CMDDIR "/usr/adm/sm.bin"
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#endif
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/* characters disallowed in the shell "-c" argument */
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#define SPECIALS "<|>^();&`$\r\n"
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/* default search path */
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#ifndef PATH
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# define PATH "/bin:/usr/bin:/usr/ucb"
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#endif
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main(argc, argv)
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int argc;
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char **argv;
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{
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register char *p;
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register char *q;
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register char *cmd;
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int i;
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char *newenv[2];
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char cmdbuf[1000];
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char pathbuf[1000];
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#ifndef LOG_MAIL
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openlog("smrsh", 0);
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#else
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openlog("smrsh", LOG_ODELAY|LOG_CONS, LOG_MAIL);
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#endif
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strcpy(pathbuf, "PATH=");
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strcat(pathbuf, PATH);
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newenv[0] = pathbuf;
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newenv[1] = NULL;
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/*
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** Do basic argv usage checking
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*/
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if (argc != 3 || strcmp(argv[1], "-c") != 0)
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{
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fprintf(stderr, "Usage: %s -c command\n", argv[0]);
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syslog(LOG_ERR, "usage");
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exit(EX_USAGE);
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}
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/*
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** Disallow special shell syntax. This is overly restrictive,
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** but it should shut down all attacks.
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** Be sure to include 8-bit versions, since many shells strip
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** the address to 7 bits before checking.
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*/
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strcpy(cmdbuf, SPECIALS);
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for (p = cmdbuf; *p != '\0'; p++)
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*p |= '\200';
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strcat(cmdbuf, SPECIALS);
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p = strpbrk(argv[2], cmdbuf);
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if (p != NULL)
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{
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fprintf(stderr, "%s: cannot use %c in command\n",
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argv[0], *p);
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syslog(LOG_CRIT, "uid %d: attempt to use %c in command: %s",
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getuid(), *p, argv[2]);
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exit(EX_UNAVAILABLE);
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}
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/*
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** Do a quick sanity check on command line length.
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*/
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i = strlen(argv[2]);
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if (i > (sizeof cmdbuf - sizeof CMDDIR - 2))
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{
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fprintf(stderr, "%s: command too long: %s\n", argv[0], argv[2]);
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syslog(LOG_WARNING, "command too long: %.40s", argv[2]);
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exit(EX_UNAVAILABLE);
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}
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/*
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** Strip off a leading pathname on the command name. For
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** example, change /usr/ucb/vacation to vacation.
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*/
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/* strip leading spaces */
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for (q = argv[2]; *q != '\0' && isascii(*q) && isspace(*q); )
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q++;
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/* find the end of the command name */
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p = strpbrk(q, " \t");
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if (p == NULL)
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cmd = &q[strlen(q)];
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else
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{
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*p = '\0';
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cmd = p;
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}
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/* search backwards for last / (allow for 0200 bit) */
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while (cmd > q)
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{
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if ((*--cmd & 0177) == '/')
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{
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cmd++;
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break;
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}
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}
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/* cmd now points at final component of path name */
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/*
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** Check to see if the command name is legal.
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*/
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(void) strcpy(cmdbuf, CMDDIR);
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(void) strcat(cmdbuf, "/");
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(void) strcat(cmdbuf, cmd);
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#ifdef DEBUG
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printf("Trying %s\n", cmdbuf);
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#endif
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if (access(cmdbuf, X_OK) < 0)
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{
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/* oops.... crack attack possiblity */
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fprintf(stderr, "%s: %s not available for sendmail programs\n",
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argv[0], cmd);
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if (p != NULL)
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*p = ' ';
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syslog(LOG_CRIT, "uid %d: attempt to use %s", getuid(), cmd);
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exit(EX_UNAVAILABLE);
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}
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if (p != NULL)
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*p = ' ';
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/*
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** Create the actual shell input.
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*/
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strcpy(cmdbuf, CMDDIR);
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strcat(cmdbuf, "/");
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strcat(cmdbuf, cmd);
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/*
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** Now invoke the shell
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*/
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#ifdef DEBUG
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printf("%s\n", cmdbuf);
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#endif
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execle("/bin/sh", "/bin/sh", "-c", cmdbuf, NULL, newenv);
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syslog(LOG_CRIT, "Cannot exec /bin/sh: %m");
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perror("/bin/sh");
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exit(EX_OSFILE);
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}
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