ref: 2c9e3861a54e22498fb2e3226defe4393b20b202
dir: /sys/src/cmd/python/Misc/setuid-prog.c/
/*
Template for a setuid program that calls a script.
The script should be in an unwritable directory and should itself
be unwritable. In fact all parent directories up to the root
should be unwritable. The script must not be setuid, that's what
this program is for.
This is a template program. You need to fill in the name of the
script that must be executed. This is done by changing the
definition of FULL_PATH below.
There are also some rules that should be adhered to when writing
the script itself.
The first and most important rule is to never, ever trust that the
user of the program will behave properly. Program defensively.
Check your arguments for reasonableness. If the user is allowed to
create files, check the names of the files. If the program depends
on argv[0] for the action it should perform, check it.
Assuming the script is a Bourne shell script, the first line of the
script should be
#!/bin/sh -
The - is important, don't omit it. If you're using esh, the first
line should be
#!/usr/local/bin/esh -f
and for ksh, the first line should be
#!/usr/local/bin/ksh -p
The script should then set the variable IFS to the string
consisting of <space>, <tab>, and <newline>. After this (*not*
before!), the PATH variable should be set to a reasonable value and
exported. Do not expect the PATH to have a reasonable value, so do
not trust the old value of PATH. You should then set the umask of
the program by calling
umask 077 # or 022 if you want the files to be readable
If you plan to change directories, you should either unset CDPATH
or set it to a good value. Setting CDPATH to just ``.'' (dot) is a
good idea.
If, for some reason, you want to use csh, the first line should be
#!/bin/csh -fb
You should then set the path variable to something reasonable,
without trusting the inherited path. Here too, you should set the
umask using the command
umask 077 # or 022 if you want the files to be readable
*/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
/* CONFIGURATION SECTION */
#ifndef FULL_PATH /* so that this can be specified from the Makefile */
/* Uncomment the following line:
#define FULL_PATH "/full/path/of/script"
* Then comment out the #error line. */
#error "You must define FULL_PATH somewhere"
#endif
#ifndef UMASK
#define UMASK 077
#endif
/* END OF CONFIGURATION SECTION */
#if defined(__STDC__) && defined(__sgi)
#define environ _environ
#endif
/* don't change def_IFS */
char def_IFS[] = "IFS= \t\n";
/* you may want to change def_PATH, but you should really change it in */
/* your script */
#ifdef __sgi
char def_PATH[] = "PATH=/usr/bsd:/usr/bin:/bin:/usr/local/bin:/usr/sbin";
#else
char def_PATH[] = "PATH=/usr/ucb:/usr/bin:/bin:/usr/local/bin";
#endif
/* don't change def_CDPATH */
char def_CDPATH[] = "CDPATH=.";
/* don't change def_ENV */
char def_ENV[] = "ENV=:";
/*
This function changes all environment variables that start with LD_
into variables that start with XD_. This is important since we
don't want the script that is executed to use any funny shared
libraries.
The other changes to the environment are, strictly speaking, not
needed here. They can safely be done in the script. They are done
here because we don't trust the script writer (just like the script
writer shouldn't trust the user of the script).
If IFS is set in the environment, set it to space,tab,newline.
If CDPATH is set in the environment, set it to ``.''.
Set PATH to a reasonable default.
*/
void
clean_environ(void)
{
char **p;
extern char **environ;
for (p = environ; *p; p++) {
if (strncmp(*p, "LD_", 3) == 0)
**p = 'X';
else if (strncmp(*p, "_RLD", 4) == 0)
**p = 'X';
else if (strncmp(*p, "PYTHON", 6) == 0)
**p = 'X';
else if (strncmp(*p, "IFS=", 4) == 0)
*p = def_IFS;
else if (strncmp(*p, "CDPATH=", 7) == 0)
*p = def_CDPATH;
else if (strncmp(*p, "ENV=", 4) == 0)
*p = def_ENV;
}
putenv(def_PATH);
}
int
main(int argc, char **argv)
{
struct stat statb;
gid_t egid = getegid();
uid_t euid = geteuid();
/*
Sanity check #1.
This check should be made compile-time, but that's not possible.
If you're sure that you specified a full path name for FULL_PATH,
you can omit this check.
*/
if (FULL_PATH[0] != '/') {
fprintf(stderr, "%s: %s is not a full path name\n", argv[0],
FULL_PATH);
fprintf(stderr, "You can only use this wrapper if you\n");
fprintf(stderr, "compile it with an absolute path.\n");
exit(1);
}
/*
Sanity check #2.
Check that the owner of the script is equal to either the
effective uid or the super user.
*/
if (stat(FULL_PATH, &statb) < 0) {
perror("stat");
exit(1);
}
if (statb.st_uid != 0 && statb.st_uid != euid) {
fprintf(stderr, "%s: %s has the wrong owner\n", argv[0],
FULL_PATH);
fprintf(stderr, "The script should be owned by root,\n");
fprintf(stderr, "and shouldn't be writeable by anyone.\n");
exit(1);
}
if (setregid(egid, egid) < 0)
perror("setregid");
if (setreuid(euid, euid) < 0)
perror("setreuid");
clean_environ();
umask(UMASK);
while (**argv == '-') /* don't let argv[0] start with '-' */
(*argv)++;
execv(FULL_PATH, argv);
fprintf(stderr, "%s: could not execute the script\n", argv[0]);
exit(1);
}