uid.c

   1 #include <errno.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <string.h>
   5 #include <unistd.h>
   6 #include <sys/types.h>
   7 #include <pwd.h>
   8 #include <grp.h>
   9 #include "log.h"
  10 #include "params.h"
  11 #include "uid.h"
  12
  13 uid_t orig_uid;
  14 gid_t orig_gid;
  15
  16 uid_t nobody_uid;
  17 gid_t nobody_gid;
  18
  19 void dump_uids(void)
  20 {
  21         uid_t uid, euid, suid;
  22         gid_t gid, egid, sgid;
  23
  24         getresuid(&uid, &euid, &suid);
  25         getresgid(&gid, &egid, &sgid);
  26
  27         outputstd("initial uid:%d gid:%d euid:%d egid:%d suid:%d sgid:%d\n",
  28                 uid, gid, euid, egid, suid, sgid);
  29 }
  30
  31 void drop_privs(void)
  32 {
  33         if (setresgid(nobody_gid, nobody_gid, nobody_gid) < 0) {
  34                 outputerr("Error setting nobody gid (%s)\n", strerror(errno));
  35                 exit(EXIT_FAILURE);
  36         }
  37
  38         if (setgroups(0, NULL) == -1) {
  39                 outputerr("Error dropping supplemental groups (%s)\n", strerror(errno));
  40                 exit(EXIT_FAILURE);
  41         }
  42
  43         if (setresuid(nobody_uid, nobody_uid, nobody_uid) < 0) {
  44                 outputerr("Error setting nobody uid (%s)\n", strerror(errno));
  45                 exit(EXIT_FAILURE);
  46         }
  47
  48         outputstd("set uid to %d and gid to %d (nobody)\n", nobody_uid, nobody_gid);
  49 }
  50
  51 void init_uids(void)
  52 {
  53         struct passwd *passwd;
  54
  55         orig_uid = getuid();
  56         orig_gid = getgid();
  57
  58         passwd = getpwnam("nobody");
  59         if (passwd == NULL) {
  60                 outputerr("Error getting nobody pwent (%s)\n", strerror(errno));
  61                 exit(EXIT_FAILURE);
  62         }
  63         nobody_uid = passwd->pw_uid;
  64         nobody_gid = passwd->pw_gid;
  65 }
  66
  67
  68 void do_uid0_check(void)
  69 {
  70         unsigned int i;
  71
  72         /* if we're already unprivileged, then don't worry. */
  73         if (orig_uid != 0)
  74                 return;
  75
  76         if (dangerous == TRUE) {
  77                 outputstd("DANGER: RUNNING AS ROOT.\n");
  78                 outputstd("Unless you are running in a virtual machine, this could cause serious problems such as overwriting CMOS\n");
  79                 outputstd("or similar which could potentially make this machine unbootable without a firmware reset.\n");
  80                 outputstd("You might want to check out running with --dropprivs (currently experimental).\n\n");
  81         } else {
  82
  83                 if (dropprivs == FALSE) {
  84                         outputstd("Don't run as root (or pass --dangerous, or --dropprivs if you know what you are doing).\n");
  85                         exit(EXIT_FAILURE);
  86                 } else {
  87                         outputstd("--dropprivs is still in development, and really shouldn't be used unless you're helping development. Expect crashes.\n");
  88                         outputstd("Going to run as user nobody (uid:%d gid:%d)\n", nobody_uid, nobody_gid);
  89                 }
  90         }
  91
  92         outputstd("ctrl-c now unless you really know what you are doing.\n");
  93         for (i = 10; i > 0; i--) {
  94                 outputstd("Continuing in %d seconds.\r", i);
  95                 (void)fflush(stdout);
  96                 sleep(1);
  97         }
  98 }
  99
 100 void check_uid(void)
 101 {
 102         uid_t myuid;
 103
 104         /* If we were root, then obviously setuid() will change us, so don't even check. */
 105         if (orig_uid == 0)
 106                 return;
 107
 108         myuid = getuid();
 109
 110         /* we should be 'nobody' if we ran with --dropprivs */
 111         if (dropprivs == TRUE) {
 112                 if (myuid == nobody_uid)
 113                         return;
 114                 else
 115                         goto changed;
 116         }
 117
 118         if (myuid != orig_uid) {
 119
 120 changed:
 121                 /* unshare() can change us to /proc/sys/kernel/overflowuid */
 122                 if (myuid == 65534)
 123                         return;
 124
 125                 output(0, "uid changed! Was: %d, now %d\n", orig_uid, myuid);
 126
 127                 shm->exit_reason = EXIT_UID_CHANGED;
 128                 _exit(EXIT_FAILURE);
 129         }
 130 }