14887Schin /***********************************************************************
24887Schin * *
34887Schin * This software is part of the ast package *
4*12068SRoger.Faulkner@Oracle.COM * Copyright (c) 1982-2010 AT&T Intellectual Property *
54887Schin * and is licensed under the *
64887Schin * Common Public License, Version 1.0 *
78462SApril.Chin@Sun.COM * by AT&T Intellectual Property *
84887Schin * *
94887Schin * A copy of the License is available at *
104887Schin * http://www.opensource.org/licenses/cpl1.0.txt *
114887Schin * (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9) *
124887Schin * *
134887Schin * Information and Software Systems Research *
144887Schin * AT&T Research *
154887Schin * Florham Park NJ *
164887Schin * *
174887Schin * David Korn <dgk@research.att.com> *
184887Schin * *
194887Schin ***********************************************************************/
204887Schin #pragma prototyped
214887Schin /*
224887Schin * This is a program to execute 'execute only' and suid/sgid shell scripts.
234887Schin * This program must be owned by root and must have the set uid bit set.
244887Schin * It must not have the set group id bit set. This program must be installed
254887Schin * where the define parameter THISPROG indicates to work correctly on system V
264887Schin *
274887Schin * Written by David Korn
284887Schin * AT&T Labs
294887Schin * Enhanced by Rob Stampfli
304887Schin */
314887Schin
324887Schin /* The file name of the script to execute is argv[0]
334887Schin * Argv[1] is the program name
344887Schin * The basic idea is to open the script as standard input, set the effective
354887Schin * user and group id correctly, and then exec the shell.
364887Schin * The complicated part is getting the effective uid of the caller and
374887Schin * setting the effective uid/gid. The program which execs this program
384887Schin * may pass file descriptor FDIN as an open file with mode SPECIAL if
394887Schin * the effective user id is not the real user id. The effective
404887Schin * user id for authentication purposes will be the owner of this
414887Schin * open file. On systems without the setreuid() call, e[ug]id is set
424887Schin * by copying this program to a /tmp/file, making it a suid and/or sgid
434887Schin * program, and then execing this program.
444887Schin * A forked version of this program waits until it can unlink the /tmp
454887Schin * file and then exits. Actually, we fork() twice so the parent can
464887Schin * wait for the child to complete. A pipe is used to guarantee that we
474887Schin * do not remove the /tmp file too soon.
484887Schin */
494887Schin
504887Schin #include <ast.h>
514887Schin #include "FEATURE/externs"
524887Schin #include <ls.h>
534887Schin #include <sig.h>
544887Schin #include <error.h>
554887Schin #include <sys/wait.h>
564887Schin #include "version.h"
574887Schin
584887Schin #define SPECIAL 04100 /* setuid execute only by owner */
594887Schin #define FDIN 10 /* must be same as /dev/fd below */
604887Schin #undef FDSYNC
614887Schin #define FDSYNC 11 /* used on sys5 to synchronize cleanup */
624887Schin #define FDVERIFY 12 /* used to validate /tmp process */
634887Schin #undef BLKSIZE
644887Schin #define BLKSIZE sizeof(char*)*1024
654887Schin #define THISPROG "/etc/suid_exec"
664887Schin #define DEFSHELL "/bin/sh"
674887Schin
684887Schin static void error_exit(const char*);
694887Schin static int in_dir(const char*, const char*);
704887Schin static int endsh(const char*);
714887Schin #ifndef _lib_setregid
724887Schin # undef _lib_setreuid
734887Schin #endif
744887Schin #ifndef _lib_setreuid
754887Schin static void setids(int,uid_t,gid_t);
764887Schin static int mycopy(int, int);
774887Schin static void maketemp(char*);
784887Schin #else
794887Schin static void setids(int,int,int);
804887Schin #endif /* _lib_setreuid */
814887Schin
824887Schin static const char version[] = "\n@(#)$Id: suid_exec "SH_RELEASE" $\n";
834887Schin static const char badopen[] = "cannot open";
844887Schin static const char badexec[] = "cannot exec";
854887Schin static const char devfd[] = "/dev/fd/10"; /* must match FDIN above */
864887Schin static char tmpname[] = "/tmp/SUIDXXXXXX";
874887Schin static char **arglist;
884887Schin
894887Schin static char *shell;
904887Schin static char *command;
914887Schin static uid_t ruserid;
924887Schin static uid_t euserid;
934887Schin static gid_t rgroupid;
944887Schin static gid_t egroupid;
954887Schin static struct stat statb;
964887Schin
main(int argc,char * argv[])974887Schin int main(int argc,char *argv[])
984887Schin {
994887Schin register int m,n;
1004887Schin register char *p;
1014887Schin struct stat statx;
1024887Schin int mode;
1034887Schin uid_t effuid;
1044887Schin gid_t effgid;
1054887Schin NOT_USED(argc);
1064887Schin arglist = argv;
1074887Schin if((command = argv[1]) == 0)
1084887Schin error_exit(badexec);
1094887Schin ruserid = getuid();
1104887Schin euserid = geteuid();
1114887Schin rgroupid = getgid();
1124887Schin egroupid = getegid();
1134887Schin p = argv[0];
1144887Schin #ifndef _lib_setreuid
1154887Schin maketemp(tmpname);
1164887Schin if(strcmp(p,tmpname)==0)
1174887Schin {
1184887Schin /* At this point, the presumption is that we are the
1194887Schin * version of THISPROG copied into /tmp, with the owner,
1204887Schin * group, and setuid/gid bits correctly set. This copy of
1214887Schin * the program is executable by anyone, so we must be careful
1224887Schin * not to allow just any invocation of it to succeed, since
1234887Schin * it is setuid/gid. Validate the proper execution by
1244887Schin * examining the FDVERIFY file descriptor -- if it is owned
1254887Schin * by root and is mode SPECIAL, then this is proof that it was
1264887Schin * passed by a program with superuser privileges -- hence we
1274887Schin * can presume legitimacy. Otherwise, bail out, as we suspect
1284887Schin * an impostor.
1294887Schin */
1304887Schin if(fstat(FDVERIFY,&statb) < 0 || statb.st_uid != 0 ||
1314887Schin (statb.st_mode & ~S_IFMT) != SPECIAL || close(FDVERIFY)<0)
1324887Schin error_exit(badexec);
1334887Schin /* This enables the grandchild to clean up /tmp file */
1344887Schin close(FDSYNC);
1354887Schin /* Make sure that this is a valid invocation of the clone.
1364887Schin * Perhaps unnecessary, given FDVERIFY, but what the heck...
1374887Schin */
1384887Schin if(stat(tmpname,&statb) < 0 || statb.st_nlink != 1 ||
1394887Schin !S_ISREG(statb.st_mode))
1404887Schin error_exit(badexec);
1414887Schin if(ruserid != euserid &&
1424887Schin ((statb.st_mode & S_ISUID) == 0 || statb.st_uid != euserid))
1434887Schin error_exit(badexec);
1444887Schin goto exec;
1454887Schin }
1464887Schin /* Make sure that this is the real setuid program, not the clone.
1474887Schin * It is possible by clever hacking to get past this point in the
1484887Schin * clone, but it doesn't do the hacker any good that I can see.
1494887Schin */
1504887Schin if(euserid)
1514887Schin error_exit(badexec);
1524887Schin #endif /* _lib_setreuid */
1534887Schin /* Open the script for reading first and then validate it. This
1544887Schin * prevents someone from pulling a switcheroo while we are validating.
1554887Schin */
1564887Schin n = open(p,0);
1574887Schin if(n == FDIN)
1584887Schin {
1594887Schin n = dup(n);
1604887Schin close(FDIN);
1614887Schin }
1624887Schin if(n < 0)
1634887Schin error_exit(badopen);
1644887Schin /* validate execution rights to this script */
1654887Schin if(fstat(FDIN,&statb) < 0 || (statb.st_mode & ~S_IFMT) != SPECIAL)
1664887Schin euserid = ruserid;
1674887Schin else
1684887Schin euserid = statb.st_uid;
1694887Schin /* do it the easy way if you can */
1704887Schin if(euserid == ruserid && egroupid == rgroupid)
1714887Schin {
1724887Schin if(access(p,X_OK) < 0)
1734887Schin error_exit(badexec);
1744887Schin }
1754887Schin else
1764887Schin {
1774887Schin /* have to check access on each component */
1784887Schin while(*p++)
1794887Schin {
1804887Schin if(*p == '/' || *p == 0)
1814887Schin {
1824887Schin m = *p;
1834887Schin *p = 0;
1844887Schin if(eaccess(argv[0],X_OK) < 0)
1854887Schin error_exit(badexec);
1864887Schin *p = m;
1874887Schin }
1884887Schin }
1894887Schin p = argv[0];
1904887Schin }
1914887Schin if(fstat(n, &statb) < 0 || !S_ISREG(statb.st_mode))
1924887Schin error_exit(badopen);
1934887Schin if(stat(p, &statx) < 0 ||
1944887Schin statb.st_ino != statx.st_ino || statb.st_dev != statx.st_dev)
1954887Schin error_exit(badexec);
1964887Schin if(stat(THISPROG, &statx) < 0 ||
1974887Schin (statb.st_ino == statx.st_ino && statb.st_dev == statx.st_dev))
1984887Schin error_exit(badexec);
1994887Schin close(FDIN);
2004887Schin if(fcntl(n,F_DUPFD,FDIN) != FDIN)
2014887Schin error_exit(badexec);
2024887Schin close(n);
2034887Schin
2044887Schin /* compute the desired new effective user and group id */
2054887Schin effuid = euserid;
2064887Schin effgid = egroupid;
2074887Schin mode = 0;
2084887Schin if(statb.st_mode & S_ISUID)
2094887Schin effuid = statb.st_uid;
2104887Schin if(statb.st_mode & S_ISGID)
2114887Schin effgid = statb.st_gid;
2124887Schin
2134887Schin /* see if group needs setting */
2144887Schin if(effgid != egroupid)
2154887Schin if(effgid != rgroupid || setgid(rgroupid) < 0)
2164887Schin mode = S_ISGID;
2174887Schin
2184887Schin /* now see if the uid needs setting */
2194887Schin if(mode)
2204887Schin {
2214887Schin if(effuid != ruserid)
2224887Schin mode |= S_ISUID;
2234887Schin }
2244887Schin else if(effuid)
2254887Schin {
2264887Schin if(effuid != ruserid || setuid(ruserid) < 0)
2274887Schin mode = S_ISUID;
2284887Schin }
2294887Schin
2304887Schin if(mode)
2314887Schin setids(mode, effuid, effgid);
2324887Schin #ifndef _lib_setreuid
2334887Schin exec:
2344887Schin #endif /* _lib_setreuid */
2354887Schin /* only use SHELL if file is in trusted directory and ends in sh */
2364887Schin shell = getenv("SHELL");
2374887Schin if(shell == 0 || !endsh(shell) || (
2384887Schin !in_dir("/bin",shell) &&
2394887Schin !in_dir("/usr/bin",shell) &&
2404887Schin !in_dir("/usr/lbin",shell) &&
2414887Schin !in_dir("/usr/local/bin",shell)))
2424887Schin shell = DEFSHELL;
2434887Schin argv[0] = command;
2444887Schin argv[1] = (char*)devfd;
2454887Schin execv(shell,argv);
2464887Schin error_exit(badexec);
2474887Schin }
2484887Schin
2494887Schin /*
2504887Schin * return true of shell ends in sh of ksh
2514887Schin */
2524887Schin
endsh(register const char * shell)2534887Schin static int endsh(register const char *shell)
2544887Schin {
2554887Schin while(*shell)
2564887Schin shell++;
2574887Schin if(*--shell != 'h' || *--shell != 's')
2584887Schin return(0);
2594887Schin if(*--shell=='/')
2604887Schin return(1);
2614887Schin if(*shell=='k' && *--shell=='/')
2624887Schin return(1);
2634887Schin return(0);
2644887Schin }
2654887Schin
2664887Schin
2674887Schin /*
2684887Schin * return true of shell is in <dir> directory
2694887Schin */
2704887Schin
in_dir(register const char * dir,register const char * shell)2714887Schin static int in_dir(register const char *dir,register const char *shell)
2724887Schin {
2734887Schin while(*dir)
2744887Schin {
2754887Schin if(*dir++ != *shell++)
2764887Schin return(0);
2774887Schin }
2784887Schin /* return true if next character is a '/' */
2794887Schin return(*shell=='/');
2804887Schin }
2814887Schin
error_exit(const char * message)2824887Schin static void error_exit(const char *message)
2834887Schin {
2844887Schin sfprintf(sfstdout,"%s: %s\n",command,message);
2854887Schin exit(126);
2864887Schin }
2874887Schin
2884887Schin
2894887Schin /*
2904887Schin * This version of access checks against effective uid and effective gid
2914887Schin */
2924887Schin
eaccess(register const char * name,register int mode)2934887Schin int eaccess(register const char *name, register int mode)
2944887Schin {
2954887Schin struct stat statb;
2964887Schin if (stat(name, &statb) == 0)
2974887Schin {
2984887Schin if(euserid == 0)
2994887Schin {
3004887Schin if(!S_ISREG(statb.st_mode) || mode != 1)
3014887Schin return(0);
3024887Schin /* root needs execute permission for someone */
3034887Schin mode = (S_IXUSR|S_IXGRP|S_IXOTH);
3044887Schin }
3054887Schin else if(euserid == statb.st_uid)
3064887Schin mode <<= 6;
3074887Schin else if(egroupid == statb.st_gid)
3084887Schin mode <<= 3;
3094887Schin #ifdef _lib_getgroups
3104887Schin /* on some systems you can be in several groups */
3114887Schin else
3124887Schin {
3134887Schin static int maxgroups;
3144887Schin gid_t *groups=0;
3154887Schin register int n;
3164887Schin if(maxgroups==0)
3174887Schin {
3184887Schin /* first time */
3194887Schin if((maxgroups=getgroups(0,groups)) < 0)
3204887Schin {
3214887Schin /* pre-POSIX system */
3224887Schin maxgroups=NGROUPS_MAX;
3234887Schin }
3244887Schin }
3254887Schin groups = (gid_t*)malloc((maxgroups+1)*sizeof(gid_t));
3264887Schin n = getgroups(maxgroups,groups);
3274887Schin while(--n >= 0)
3284887Schin {
3294887Schin if(groups[n] == statb.st_gid)
3304887Schin {
3314887Schin mode <<= 3;
3324887Schin break;
3334887Schin }
3344887Schin }
3354887Schin }
3364887Schin #endif /* _lib_getgroups */
3374887Schin if(statb.st_mode & mode)
3384887Schin return(0);
3394887Schin }
3404887Schin return(-1);
3414887Schin }
3424887Schin
3434887Schin #ifdef _lib_setreuid
setids(int mode,int owner,int group)3444887Schin static void setids(int mode,int owner,int group)
3454887Schin {
3464887Schin if(mode & S_ISGID)
3474887Schin setregid(rgroupid,group);
3484887Schin
3494887Schin /* set effective uid even if S_ISUID is not set. This is because
3504887Schin * we are *really* executing EUID root at this point. Even if S_ISUID
3514887Schin * is not set, the value for owner that is passsed should be correct.
3524887Schin */
3534887Schin setreuid(ruserid,owner);
3544887Schin }
3554887Schin
3564887Schin #else
3574887Schin /*
3584887Schin * This version of setids creats a /tmp file and copies itself into it.
3594887Schin * The "clone" file is made executable with appropriate suid/sgid bits.
3604887Schin * Finally, the clone is exec'ed. This file is unlinked by a grandchild
3614887Schin * of this program, who waits around until the text is free.
3624887Schin */
3634887Schin
setids(int mode,uid_t owner,gid_t group)3644887Schin static void setids(int mode,uid_t owner,gid_t group)
3654887Schin {
3664887Schin register int n,m;
3674887Schin int pv[2];
3684887Schin
3694887Schin /*
3704887Schin * Create a token to pass to the new program for validation.
3714887Schin * This token can only be procured by someone running with an
3724887Schin * effective userid of root, and hence gives the clone a way to
3734887Schin * certify that it was really invoked by THISPROG. Someone who
3744887Schin * is already root could spoof us, but why would they want to?
3754887Schin *
3764887Schin * Since we are root here, we must be careful: What if someone
3774887Schin * linked a valuable file to tmpname?
3784887Schin */
3794887Schin unlink(tmpname); /* should normally fail */
3804887Schin #ifdef O_EXCL
3814887Schin if((n = open(tmpname, O_WRONLY | O_CREAT | O_EXCL, SPECIAL)) < 0 ||
3824887Schin unlink(tmpname) < 0)
3834887Schin #else
3844887Schin if((n = open(tmpname, O_WRONLY | O_CREAT ,SPECIAL)) < 0 || unlink(tmpname) < 0)
3854887Schin #endif
3864887Schin error_exit(badexec);
3874887Schin if(n != FDVERIFY)
3884887Schin {
3894887Schin close(FDVERIFY);
3904887Schin if(fcntl(n,F_DUPFD,FDVERIFY) != FDVERIFY)
3914887Schin error_exit(badexec);
3924887Schin }
3934887Schin mode |= S_IEXEC|(S_IEXEC>>3)|(S_IEXEC>>6);
3944887Schin /* create a pipe for synchronization */
3954887Schin if(pipe(pv) < 0)
3964887Schin error_exit(badexec);
3974887Schin if((n=fork()) == 0)
3984887Schin { /* child */
3994887Schin close(FDVERIFY);
4004887Schin close(pv[1]);
4014887Schin if((n=fork()) == 0)
4024887Schin { /* grandchild -- cleans up clone file */
4034887Schin signal(SIGHUP, SIG_IGN);
4044887Schin signal(SIGINT, SIG_IGN);
4054887Schin signal(SIGQUIT, SIG_IGN);
4064887Schin signal(SIGTERM, SIG_IGN);
4074887Schin read(pv[0],pv,1); /* wait for clone to close pipe */
4084887Schin while(unlink(tmpname) < 0 && errno == ETXTBSY)
4094887Schin sleep(1);
4104887Schin exit(0);
4114887Schin }
4124887Schin else if(n == -1)
4134887Schin exit(1);
4144887Schin else
4154887Schin {
4164887Schin /* Create a set[ug]id file that will become the clone.
4174887Schin * To make this atomic, without need for chown(), the
4184887Schin * child takes on desired user and group. The only
4194887Schin * downsize of this that I can see is that it may
4204887Schin * screw up some per- * user accounting.
4214887Schin */
4224887Schin if((m = open(THISPROG, O_RDONLY)) < 0)
4234887Schin exit(1);
4244887Schin if((mode & S_ISGID) && setgid(group) < 0)
4254887Schin exit(1);
4264887Schin if((mode & S_ISUID) && owner && setuid(owner) < 0)
4274887Schin exit(1);
4284887Schin #ifdef O_EXCL
4294887Schin if((n = open(tmpname,O_WRONLY|O_CREAT|O_TRUNC|O_EXCL, mode)) < 0)
4304887Schin #else
4314887Schin unlink(tmpname);
4324887Schin if((n = open(tmpname,O_WRONLY|O_CREAT|O_TRUNC, mode)) < 0)
4334887Schin #endif /* O_EXCL */
4344887Schin exit(1);
4354887Schin /* populate the clone */
4364887Schin m = mycopy(m,n);
4374887Schin if(chmod(tmpname,mode) <0)
4384887Schin exit(1);
4394887Schin exit(m);
4404887Schin }
4414887Schin }
4424887Schin else if(n == -1)
4434887Schin error_exit(badexec);
4444887Schin else
4454887Schin {
4464887Schin arglist[0] = (char*)tmpname;
4474887Schin close(pv[0]);
4484887Schin /* move write end of pipe into FDSYNC */
4494887Schin if(pv[1] != FDSYNC)
4504887Schin {
4514887Schin close(FDSYNC);
4524887Schin if(fcntl(pv[1],F_DUPFD,FDSYNC) != FDSYNC)
4534887Schin error_exit(badexec);
4544887Schin }
4554887Schin /* wait for child to die */
4564887Schin while((m = wait(0)) != n)
4574887Schin if(m == -1 && errno != EINTR)
4584887Schin break;
4594887Schin /* Kill any setuid status at this point. That way, if the
4604887Schin * clone is not setuid, we won't exec it as root. Also, don't
4614887Schin * neglect to consider that someone could have switched the
4624887Schin * clone file on us.
4634887Schin */
4644887Schin if(setuid(ruserid) < 0)
4654887Schin error_exit(badexec);
4664887Schin execv(tmpname,arglist);
4674887Schin error_exit(badexec);
4684887Schin }
4694887Schin }
4704887Schin
4714887Schin /*
4724887Schin * create a unique name into the <template>
4734887Schin */
4744887Schin
maketemp(char * template)4754887Schin static void maketemp(char *template)
4764887Schin {
4774887Schin register char *cp = template;
4784887Schin register pid_t n = getpid();
4794887Schin /* skip to end of string */
4804887Schin while(*++cp);
4814887Schin /* convert process id to string */
4824887Schin while(n > 0)
4834887Schin {
4844887Schin *--cp = (n%10) + '0';
4854887Schin n /= 10;
4864887Schin }
4874887Schin
4884887Schin }
4894887Schin
4904887Schin /*
4914887Schin * copy THISPROG into the open file number <fdo> and close <fdo>
4924887Schin */
4934887Schin
mycopy(int fdi,int fdo)4944887Schin static int mycopy(int fdi, int fdo)
4954887Schin {
4964887Schin char buffer[BLKSIZE];
4974887Schin register int n;
4984887Schin
4994887Schin while((n = read(fdi,buffer,BLKSIZE)) > 0)
5004887Schin if(write(fdo,buffer,n) != n)
5014887Schin break;
5024887Schin close(fdi);
5034887Schin close(fdo);
5044887Schin return n;
5054887Schin }
5064887Schin
5074887Schin #endif /* _lib_setreuid */
5084887Schin
5094887Schin
510