511 lines
12 KiB
C
511 lines
12 KiB
C
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/* */
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/* Copyright (c) 1984,1985,1986,1987,1988,1989,1990 AT&T */
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/* All Rights Reserved */
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/* */
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/* THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF AT&T. */
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/* The copyright notice above does not evidence any */
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/* actual or intended publication of such source code. */
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/* */
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/*
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* This is a program to execute 'execute only' and suid/sgid shell scripts.
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* This program must be owned by root and must have the suid bit set. It must
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* not have the guid bit set. This program must be installed where the
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* define parameter THISPROG indicates to work correctly on system V machines.
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*
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* Written by David Korn
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* AT&T Bell Laboratories
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* ulysses!dgk
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* Enhanced by Rob Stampfli
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* AT&T Bell Laboratories
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*/
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/* The file name of the script to execute is argv[0]
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* Argv[1] is the program name
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* The basic idea is to open the script as standard input, set the effective
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* user and group id correctly, and then exec the shell.
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* The complicated part is getting the effective uid of the caller and
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* setting the effective uid/gid. The program which execs this program
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* may pass file descriptor FDIN as an open file with mode SPECIAL if
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* the effective user id is not the real user id. The effective
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* user id for authentication purposes will be the owner of this
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* open file. On systems without the setreuid() call, e[ug]id is set
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* by copying this program to a /tmp/file, making it a suid and/or sgid
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* program, and then execing this program.
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* A forked version of this program waits until it can unlink the /tmp
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* file and then exits. Actually, we fork() twice so the parent can
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* wait for the child to complete. A pipe is used to guarantee that we
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* do not remove the /tmp file too soon.
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*/
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#include "sh_config.h"
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#ifdef _fcntl_
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# include <fcntl.h>
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# ifndef F_DUPFD
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# define fcntl(a,b,c) dup2(a,c)
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# endif /* F_DUPFD */
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#else
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# define fcntl(a,b,c) dup2(a,c)
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#endif /* _fcntl_ */
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#ifdef _unistd_
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# include <unistd.h>
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#endif /* _unistd_ */
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#include <sys/stat.h>
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#include <signal.h>
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#include <errno.h>
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#include <stdlib.h>
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#ifdef sgi
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#define stat stat64
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#define fstat fstat64
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#endif
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#ifndef X_OK
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# define X_OK 1
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#endif /* X_OK */
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#define SPECIAL 04100 /* setuid execute only by owner */
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#define FDIN 10 /* must be same as /dev/fd below */
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#define FDCLSYNC 11 /* used on sys5 to synchronize cleanup */
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#define FDVERIFY 12 /* used to validate /tmp process */
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#define BLKSIZE sizeof(char*)*1024
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#define THISPROG "/etc/suid_exec"
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#define DEFSHELL "/bin/sh"
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#ifndef sgi
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extern char *getenv();
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#endif
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extern int errno;
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static void setids();
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static void error();
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static int in_dir();
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static int endsh();
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#ifndef SETREUID
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static int copy();
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static void mktemp();
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#endif /* SETREUID */
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static char version[] = "\n@(#)suid_exec 11/16/88e-Beta1\n";
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static char tmpname[] = "/tmp/SUIDXXXXXX";
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static char badopen[] = "cannot open";
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static char badexec[] = "cannot exec";
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static char devfd[] = "/dev/fd/10"; /* must match FDIN above */
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static char **arglist;
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static char *shell;
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static char *command;
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static uid_t ruserid;
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static uid_t euserid;
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static gid_t rgroupid;
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static gid_t egroupid;
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static struct stat statb;
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main(argc,argv)
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char *argv[];
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{
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register int m,n;
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register char *p;
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struct stat statx;
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int mode;
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uid_t effuid;
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gid_t effgid;
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arglist = argv;
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if((command = argv[1]) == 0)
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error(badexec);
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ruserid = getuid();
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euserid = geteuid();
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rgroupid = getgid();
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egroupid = getegid();
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p = argv[0];
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#ifndef SETREUID
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mktemp(tmpname);
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if(strcmp(p,tmpname)==0)
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{
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/* At this point, the presumption is that we are the
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* version of THISPROG copied into /tmp, with the owner,
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* group, and setuid/gid bits correctly set. This copy of
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* the program is executable by anyone, so we must be careful
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* not to allow just any invocation of it to succeed, since
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* it is setuid/gid. Validate the proper execution by
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* examining the FDVERIFY file descriptor -- if it is owned
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* by root and is mode SPECIAL, then this is proof that it was
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* passed by a program with superuser privileges -- hence we
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* can presume legitimacy. Otherwise, bail out, as we suspect
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* an impostor.
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*/
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if(fstat(FDVERIFY,&statb) < 0 || statb.st_uid != 0 ||
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(statb.st_mode & ~S_IFMT) != SPECIAL || close(FDVERIFY)<0)
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error(badexec);
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/* This enables the grandchild to clean up /tmp file */
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close(FDCLSYNC);
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/* Make sure that this is a valid invocation of the clone.
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* Perhaps unnecessary, given FDVERIFY, but what the heck...
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*/
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if(stat(tmpname,&statb) < 0 || statb.st_nlink != 1 ||
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(statb.st_mode & S_IFMT) != S_IFREG)
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error(badexec);
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if(ruserid != euserid &&
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((statb.st_mode & S_ISUID) == 0 || statb.st_uid != euserid))
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error(badexec);
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goto exec;
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}
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/* Make sure that this is the real setuid program, not the clone.
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* It is possible by clever hacking to get past this point in the
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* clone, but it doesn't do the hacker any good that I can see.
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*/
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if(euserid)
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error(badexec);
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#endif /* SETREUID */
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/* Open the script for reading first and then validate it. This
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* prevents someone from pulling a switcheroo while we are validating.
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*/
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n = open(p,0);
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if(n == FDIN)
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{
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n = dup(n);
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close(FDIN);
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}
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if(n < 0)
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error(badopen);
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/* validate execution rights to this script */
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if(fstat(FDIN,&statb) < 0 || (statb.st_mode & ~S_IFMT) != SPECIAL)
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euserid = ruserid;
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else
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euserid = statb.st_uid;
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/* do it the easy way if you can */
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if(euserid == ruserid && egroupid == rgroupid)
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{
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if(access(p,X_OK) < 0)
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error(badexec);
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}
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else
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{
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/* have to check access on each component */
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while(*p++)
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{
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if(*p == '/' || *p == 0)
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{
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m = *p;
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*p = 0;
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if(eaccess(argv[0],X_OK) < 0)
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error(badexec);
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*p = m;
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}
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}
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p = argv[0];
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}
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if(fstat(n, &statb) < 0 ||
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(statb.st_mode & S_IFMT) != S_IFREG)
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error(badopen);
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if(stat(p, &statx) < 0 ||
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statb.st_ino != statx.st_ino || statb.st_dev != statx.st_dev)
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error(badexec);
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if(stat(THISPROG, &statx) < 0 ||
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(statb.st_ino == statx.st_ino && statb.st_dev == statx.st_dev))
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error(badexec);
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close(FDIN);
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if(fcntl(n,F_DUPFD,FDIN) != FDIN)
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error(badexec);
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close(n);
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/* compute the desired new effective user and group id */
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effuid = euserid;
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effgid = egroupid;
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mode = 0;
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if(statb.st_mode & S_ISUID)
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effuid = statb.st_uid;
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if(statb.st_mode & S_ISGID)
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effgid = statb.st_gid;
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/* see if group needs setting */
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if(effgid != egroupid)
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if(effgid != rgroupid || setgid(rgroupid) < 0)
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mode = S_ISGID;
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/* now see if the uid needs setting */
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if(mode)
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{
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if(effuid != ruserid)
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mode |= S_ISUID;
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}
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else if(effuid)
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{
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if(effuid != ruserid || setuid(ruserid) < 0)
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mode = S_ISUID;
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}
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if(mode)
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setids(mode, effuid, effgid);
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exec:
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/* only use SHELL if file is in trusted directory and ends in sh */
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shell = getenv("SHELL");
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if(shell == 0 || !endsh(shell) || (
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!in_dir("/bin",shell) &&
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!in_dir("/usr/bin",shell) &&
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!in_dir("/usr/lbin",shell)))
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shell = DEFSHELL;
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argv[0] = command;
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argv[1] = devfd;
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execv(shell,argv);
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error(badexec);
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}
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/*
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* return true of shell ends in sh
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*/
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static int endsh(shell)
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register char *shell;
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{
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while(*shell)
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shell++;
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if(*--shell != 'h' || *--shell != 's')
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return(0);
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return(1);
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}
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/*
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* return true of shell is in <dir> directory
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*/
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static int in_dir(dir,shell)
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register char *dir;
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register char *shell;
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{
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while(*dir)
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{
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if(*dir++ != *shell++)
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return(0);
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}
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/* return true if next character is a '/' */
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return(*shell=='/');
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}
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static void error(message)
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char *message;
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{
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printf("%s: %s\n",command,message);
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exit(1);
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/*NOTREACHED*/
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}
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/*
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* This version of access checks against effective uid and effective gid
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*/
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eaccess(name, mode)
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register char *name;
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register int mode;
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{
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struct stat statb;
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if (stat(name, &statb) == 0)
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{
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if(euserid == 0)
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{
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if((statb.st_mode&S_IFMT) != S_IFREG || mode != 1)
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return(0);
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/* root needs execute permission for someone */
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mode = (S_IEXEC|(S_IEXEC>>3)|(S_IEXEC>>6));
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}
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else if(euserid == statb.st_uid)
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mode <<= 6;
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else if(egroupid == statb.st_gid)
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mode <<= 3;
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#if defined(NGROUPS) && NGROUPS>0
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/* on some systems you can be in several groups */
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else
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{
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gid_t groups[NGROUPS];
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register int n;
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n = getgroups(NGROUPS,groups);
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while(--n >= 0)
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{
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if(groups[n] == statb.st_gid)
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{
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mode <<= 3;
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break;
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}
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}
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}
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#endif /* NGROUPS */
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if(statb.st_mode & mode)
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return(0);
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}
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return(-1);
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}
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#ifdef SETREUID
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static void
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setids(mode,owner,group)
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{
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if(mode & S_ISGID)
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setregid(rgroupid,group);
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/* set effective uid even if S_ISUID is not set. This is because
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* we are *really* executing EUID root at this point. Even if S_ISUID
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* is not set, the value for owner that is passsed should be correct.
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*/
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setreuid(ruserid,owner);
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}
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#else
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/*
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* This version of setids creats a /tmp file and copies itself into it.
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* The "clone" file is made executable with appropriate suid/sgid bits.
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* Finally, the clone is exec'ed. This file is unlinked by a grandchild
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* of this program, who waits around until the text is free.
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*/
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static void
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setids(mode,owner,group)
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int mode;
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uid_t owner;
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gid_t group;
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{
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register int n,m;
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int pv[2];
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/*
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* Create a token to pass to the new program for validation.
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* This token can only be procured by someone running with an
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* effective userid of root, and hence gives the clone a way to
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* certify that it was really invoked by THISPROG. Someone who
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* is already root could spoof us, but why would they want to?
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*
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* Since we are root here, we must be careful: What if someone
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* linked a valuable file to tmpname?
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*/
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unlink(tmpname); /* should normally fail */
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#ifdef O_EXCL
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if((n = open(tmpname, O_WRONLY | O_CREAT | O_EXCL, SPECIAL)) < 0 ||
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unlink(tmpname) < 0)
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#else
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if((n = creat(tmpname, SPECIAL)) < 0 || unlink(tmpname) < 0)
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#endif
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error(badexec);
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if(n != FDVERIFY)
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{
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close(FDVERIFY);
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if(fcntl(n,F_DUPFD,FDVERIFY) != FDVERIFY)
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error(badexec);
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}
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mode |= S_IEXEC|(S_IEXEC>>3)|(S_IEXEC>>6);
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/* create a pipe for synchronization */
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if(pipe(pv) < 0)
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error(badexec);
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if((n=fork()) == 0)
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{ /* child */
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close(FDVERIFY);
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close(pv[1]);
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if((n=fork()) == 0)
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{ /* grandchild -- cleans up clone file */
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signal(SIGHUP, SIG_IGN);
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signal(SIGINT, SIG_IGN);
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signal(SIGQUIT, SIG_IGN);
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signal(SIGTERM, SIG_IGN);
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read(pv[0],pv,1); /* wait for clone to close pipe */
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while(unlink(tmpname) < 0 && errno == ETXTBSY)
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sleep(1);
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exit(0);
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}
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else if(n == -1)
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exit(1);
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else
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{
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/* Create a set[ug]id file that will become the clone.
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* To make this atomic, without need for chown(), the
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* child takes on desired user and group. The only
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* downsize of this that I can see is that it may
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* screw up some per- * user accounting.
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*/
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if((m = open(THISPROG, O_RDONLY)) < 0)
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exit(1);
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if((mode & S_ISGID) && setgid(group) < 0)
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exit(1);
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if((mode & S_ISUID) && owner && setuid(owner) < 0)
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exit(1);
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#ifdef O_EXCL
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if((n = open(tmpname, O_WRONLY | O_CREAT | O_EXCL, mode)) < 0)
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#else
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unlink(tmpname);
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if((n = creat(tmpname, mode)) < 0)
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#endif /* O_EXCL */
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exit(1);
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/* populate the clone */
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exit(copy(m,n));
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}
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}
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else if(n == -1)
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error(badexec);
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else
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{
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arglist[0] = tmpname;
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close(pv[0]);
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/* move write end of pipe into FDCLSYNC */
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if(pv[1] != FDCLSYNC)
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{
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close(FDCLSYNC);
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if(fcntl(pv[1],F_DUPFD,FDCLSYNC) != FDCLSYNC)
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error(badexec);
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}
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/* wait for child to die */
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while((m = wait(0)) != n)
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if(m == -1 && errno != EINTR)
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break;
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/* Kill any setuid status at this point. That way, if the
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* clone is not setuid, we won't exec it as root. Also, don't
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* neglect to consider that someone could have switched the
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* clone file on us.
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*/
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if(setuid(ruserid) < 0)
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error(badexec);
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execv(tmpname,arglist);
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error(badexec);
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}
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}
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/*
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* create a unique name into the <template>
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*/
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static void mktemp(template)
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char *template;
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{
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register char *cp = template;
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register pid_t n = getpid();
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/* skip to end of string */
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while(*++cp);
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/* convert process id to string */
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while(n > 0)
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{
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*--cp = (n%10) + '0';
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n /= 10;
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}
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}
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/*
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* copy THISPROG into the open file number <fdo> and close <fdo>
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*/
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static int copy(fdi, fdo)
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int fdi, fdo;
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{
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char buffer[BLKSIZE];
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register int n;
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while((n = read(fdi,buffer,BLKSIZE)) > 0)
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if(write(fdo,buffer,n) != n)
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break;
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close(fdi);
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close(fdo);
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return n;
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}
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#endif /* SETREUID */
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