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/* rpzsudo.c
*
* This is a very small binary meant to be statically linked and used in VMs by
* reprounzip. It allows to switch to any uid/gid by number instead of name,
* and doesn't require any other dependency (such as libc).
*/
#define _GNU_SOURCE
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
uid_t parse(char *arg)
{
if(arg[0] == '#')
{
char *endptr;
uid_t ret = strtol(arg + 1, &endptr, 10);
if(endptr - arg - 1 > 0 && *endptr == '\0')
return ret;
else
{
fprintf(stderr, "Invalid id\n");
exit(1);
}
}
else if(arg[0] == '\0')
{
fprintf(stderr, "Empty id\n");
exit(1);
}
else
{
fprintf(stderr, "Only numeric ids, prefixed with #, are supported\n");
exit(1);
}
}
int main(int argc, char **argv)
{
uid_t user, group;
if(argc < 5)
{
fprintf(stderr,
"Usage: rpzsudo <user> <group> <cmd> <arg0> [arg1 [...]]\n"
"Where user and group are numbers preceded with #\n"
"NOTE that this takes both cmd, the filename to execute, and "
"arg0 (usually set\nto the same string)\n");
exit(1);
}
else
{
user = parse(argv[1]);
group = parse(argv[2]);
}
if(setgroups(0, &group) != 0)
{
perror("couldn't set group list");
exit(1);
}
if(setregid(group, group) != 0)
{
perror("couldn't set gid");
exit(1);
}
if(setreuid(user, user) != 0)
{
perror("couldn't set uid");
exit(1);
}
if(execv(argv[3], argv + 4) == -1)
perror("Error: exec failed");
else
fprintf(stderr, "Error: exec returned\n");
return 1;
}