1/*
2   Template for a setuid program that calls a script.
3
4   The script should be in an unwritable directory and should itself
5   be unwritable.  In fact all parent directories up to the root
6   should be unwritable.  The script must not be setuid, that's what
7   this program is for.
8
9   This is a template program.  You need to fill in the name of the
10   script that must be executed.  This is done by changing the
11   definition of FULL_PATH below.
12
13   There are also some rules that should be adhered to when writing
14   the script itself.
15
16   The first and most important rule is to never, ever trust that the
17   user of the program will behave properly.  Program defensively.
18   Check your arguments for reasonableness.  If the user is allowed to
19   create files, check the names of the files.  If the program depends
20   on argv[0] for the action it should perform, check it.
21
22   Assuming the script is a Bourne shell script, the first line of the
23   script should be
24    #!/bin/sh -
25   The - is important, don't omit it.  If you're using esh, the first
26   line should be
27    #!/usr/local/bin/esh -f
28   and for ksh, the first line should be
29    #!/usr/local/bin/ksh -p
30   The script should then set the variable IFS to the string
31   consisting of <space>, <tab>, and <newline>.  After this (*not*
32   before!), the PATH variable should be set to a reasonable value and
33   exported.  Do not expect the PATH to have a reasonable value, so do
34   not trust the old value of PATH.  You should then set the umask of
35   the program by calling
36    umask 077 # or 022 if you want the files to be readable
37   If you plan to change directories, you should either unset CDPATH
38   or set it to a good value.  Setting CDPATH to just ``.'' (dot) is a
39   good idea.
40   If, for some reason, you want to use csh, the first line should be
41    #!/bin/csh -fb
42   You should then set the path variable to something reasonable,
43   without trusting the inherited path.  Here too, you should set the
44   umask using the command
45    umask 077 # or 022 if you want the files to be readable
46*/
47
48#include <unistd.h>
49#include <stdlib.h>
50#include <stdio.h>
51#include <sys/types.h>
52#include <sys/stat.h>
53#include <string.h>
54
55/* CONFIGURATION SECTION */
56
57#ifndef FULL_PATH       /* so that this can be specified from the Makefile */
58/* Uncomment the following line:
59#define FULL_PATH       "/full/path/of/script"
60* Then comment out the #error line. */
61#error "You must define FULL_PATH somewhere"
62#endif
63#ifndef UMASK
64#define UMASK           077
65#endif
66
67/* END OF CONFIGURATION SECTION */
68
69#if defined(__STDC__) && defined(__sgi)
70#define environ _environ
71#endif
72
73/* don't change def_IFS */
74char def_IFS[] = "IFS= \t\n";
75/* you may want to change def_PATH, but you should really change it in */
76/* your script */
77#ifdef __sgi
78char def_PATH[] = "PATH=/usr/bsd:/usr/bin:/bin:/usr/local/bin:/usr/sbin";
79#else
80char def_PATH[] = "PATH=/usr/ucb:/usr/bin:/bin:/usr/local/bin";
81#endif
82/* don't change def_CDPATH */
83char def_CDPATH[] = "CDPATH=.";
84/* don't change def_ENV */
85char def_ENV[] = "ENV=:";
86
87/*
88   This function changes all environment variables that start with LD_
89   into variables that start with XD_.  This is important since we
90   don't want the script that is executed to use any funny shared
91   libraries.
92
93   The other changes to the environment are, strictly speaking, not
94   needed here.  They can safely be done in the script.  They are done
95   here because we don't trust the script writer (just like the script
96   writer shouldn't trust the user of the script).
97   If IFS is set in the environment, set it to space,tab,newline.
98   If CDPATH is set in the environment, set it to ``.''.
99   Set PATH to a reasonable default.
100*/
101void
102clean_environ(void)
103{
104    char **p;
105    extern char **environ;
106
107    for (p = environ; *p; p++) {
108        if (strncmp(*p, "LD_", 3) == 0)
109            **p = 'X';
110        else if (strncmp(*p, "_RLD", 4) == 0)
111            **p = 'X';
112        else if (strncmp(*p, "PYTHON", 6) == 0)
113            **p = 'X';
114        else if (strncmp(*p, "IFS=", 4) == 0)
115            *p = def_IFS;
116        else if (strncmp(*p, "CDPATH=", 7) == 0)
117            *p = def_CDPATH;
118        else if (strncmp(*p, "ENV=", 4) == 0)
119            *p = def_ENV;
120    }
121    putenv(def_PATH);
122}
123
124int
125main(int argc, char **argv)
126{
127    struct stat statb;
128    gid_t egid = getegid();
129    uid_t euid = geteuid();
130
131    /*
132       Sanity check #1.
133       This check should be made compile-time, but that's not possible.
134       If you're sure that you specified a full path name for FULL_PATH,
135       you can omit this check.
136    */
137    if (FULL_PATH[0] != '/') {
138        fprintf(stderr, "%s: %s is not a full path name\n", argv[0],
139            FULL_PATH);
140        fprintf(stderr, "You can only use this wrapper if you\n");
141        fprintf(stderr, "compile it with an absolute path.\n");
142        exit(1);
143    }
144
145    /*
146       Sanity check #2.
147       Check that the owner of the script is equal to either the
148       effective uid or the super user.
149    */
150    if (stat(FULL_PATH, &statb) < 0) {
151        perror("stat");
152        exit(1);
153    }
154    if (statb.st_uid != 0 && statb.st_uid != euid) {
155        fprintf(stderr, "%s: %s has the wrong owner\n", argv[0],
156            FULL_PATH);
157        fprintf(stderr, "The script should be owned by root,\n");
158        fprintf(stderr, "and shouldn't be writeable by anyone.\n");
159        exit(1);
160    }
161
162    if (setregid(egid, egid) < 0)
163        perror("setregid");
164    if (setreuid(euid, euid) < 0)
165        perror("setreuid");
166
167    clean_environ();
168
169    umask(UMASK);
170
171    while (**argv == '-')       /* don't let argv[0] start with '-' */
172        (*argv)++;
173    execv(FULL_PATH, argv);
174    fprintf(stderr, "%s: could not execute the script\n", argv[0]);
175    exit(1);
176}
177