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         if (dropprivs == FALSE)
  59                 return;
  60
  61         passwd = getpwnam("nobody");
  62         if (passwd == NULL) {
  63                 outputerr("Error getting nobody pwent (%s)\n", strerror(errno));
  64                 exit(EXIT_FAILURE);
  65         }
  66         nobody_uid = passwd->pw_uid;
  67         nobody_gid = passwd->pw_gid;
  68 }
  69
  70
  71 void do_uid0_check(void)
  72 {
  73         unsigned int i;
  74
  75         /* if we're already unprivileged, then don't worry. */
  76         if (orig_uid != 0)
  77                 return;
  78
  79         if (dangerous == TRUE) {
  80                 outputstd("DANGER: RUNNING AS ROOT.\n");
  81                 outputstd("Unless you are running in a virtual machine, this could cause serious problems such as overwriting CMOS\n");
  82                 outputstd("or similar which could potentially make this machine unbootable without a firmware reset.\n");
  83                 outputstd("You might want to check out running with --dropprivs (currently experimental).\n\n");
  84         } else {
  85
  86                 if (dropprivs == FALSE) {
  87                         outputstd("Don't run as root (or pass --dangerous, or --dropprivs if you know what you are doing).\n");
  88                         exit(EXIT_FAILURE);
  89                 } else {
  90                         outputstd("--dropprivs is still in development, and really shouldn't be used unless you're helping development. Expect crashes.\n");
  91                         outputstd("Going to run as user nobody (uid:%d gid:%d)\n", nobody_uid, nobody_gid);
  92                 }
  93         }
  94
  95         outputstd("ctrl-c now unless you really know what you are doing.\n");
  96         for (i = 10; i > 0; i--) {
  97                 outputstd("Continuing in %d seconds.\r", i);
  98                 (void)fflush(stdout);
  99                 sleep(1);
 100         }
 101 }
 102
 103 void check_uid(void)
 104 {
 105         uid_t myuid;
 106
 107         /* If we were root, then obviously setuid() will change us, so don't even check. */
 108         if (orig_uid == 0)
 109                 return;
 110
 111         myuid = getuid();
 112
 113         /* we should be 'nobody' if we ran with --dropprivs */
 114         if (dropprivs == TRUE) {
 115                 if (myuid == nobody_uid)
 116                         return;
 117                 else
 118                         goto changed;
 119         }
 120
 121         if (myuid != orig_uid) {
 122
 123 changed:
 124                 /* unshare() can change us to /proc/sys/kernel/overflowuid */
 125                 if (myuid == 65534)
 126                         return;
 127
 128                 output(0, "uid changed! Was: %d, now %d\n", orig_uid, myuid);
 129
 130                 shm->exit_reason = EXIT_UID_CHANGED;
 131                 _exit(EXIT_FAILURE);
 132         }
 133 }