tinc-vpn.org Git - tinc/blob - src/bsd/openbsd/tincd.c

   1 #include "../../system.h"
   2
   3 #include <libgen.h>
   4 #include <assert.h>
   5
   6 #include "sandbox.h"
   7 #include "../../device.h"
   8 #include "../../logger.h"
   9 #include "../../names.h"
  10 #include "../../net.h"
  11 #include "../../sandbox.h"
  12 #include "../../script.h"
  13 #include "../../xalloc.h"
  14 #include "../../proxy.h"
  15
  16 static sandbox_level_t current_level = SANDBOX_NONE;
  17 static bool can_use_new_paths = true;
  18 static bool entered = false;
  19
  20 static bool chrooted(void) {
  21         return !(confbase && *confbase);
  22 }
  23
  24 static void create_conf_subdir(const char *name, mode_t mode) {
  25         char path[PATH_MAX];
  26         snprintf(path, sizeof(path), "%s/%s", confbase, name);
  27         mkdir(path, mode);
  28 }
  29
  30 static void open_conf_subdir(const char *name, const char *privs) {
  31         char path[PATH_MAX];
  32         snprintf(path, sizeof(path), "%s/%s", confbase, name);
  33         allow_path(path, privs);
  34 }
  35
  36 static void open_common_paths(bool can_exec) {
  37         // Dummy device uses a fake path, skip it
  38         const char *dev = strcasecmp(device, DEVICE_DUMMY) ? device : NULL;
  39
  40         // These calls must be done before the first unveil() for two reasons:
  41         //   1. the first unveil() blocks access to all other paths.
  42         //   2. unveil() remembers the exact directory and won't allow access if it's (re)created.
  43         create_conf_subdir("cache", 0777);
  44         create_conf_subdir("hosts", 0777);
  45         create_conf_subdir("invitations", 0700);
  46
  47         const unveil_path_t paths[] = {
  48                 {"/dev/random",  "r"},
  49                 {"/dev/urandom", "r"},
  50                 {confbase,       can_exec ? "rx" : "r"},
  51                 {dev,            "rw"},
  52                 {logfilename,    "rwc"},
  53                 {pidfilename,    "rwc"},
  54                 {unixsocketname, "rwc"},
  55                 {NULL,           NULL},
  56         };
  57         allow_paths(paths);
  58
  59         open_conf_subdir("cache", "rwc");
  60         open_conf_subdir("hosts", can_exec ? "rwxc" : "rwc");
  61         open_conf_subdir("invitations", "rwc");
  62 }
  63
  64 static void open_exec_paths(void) {
  65         // proxyhost was checked previously. If we're here, proxyhost
  66         // contains the path to the executable, and nothing else.
  67         const char *proxy_exec = proxytype == PROXY_EXEC ? proxyhost : NULL;
  68
  69         const unveil_path_t bin_paths[] = {
  70                 {"/bin",            "rx"},
  71                 {"/sbin",           "rx"},
  72                 {"/usr/bin",        "rx"},
  73                 {"/usr/sbin",       "rx"},
  74                 {"/usr/local/bin",  "rx"},
  75                 {"/usr/local/sbin", "rx"},
  76                 {scriptinterpreter, "rx"},
  77                 {proxy_exec,        "rx"},
  78                 {NULL,              NULL},
  79         };
  80         allow_paths(bin_paths);
  81 }
  82
  83 static bool sandbox_privs(bool can_exec) {
  84         // no mcast since multicasting should be set up by now
  85         char promises[512] =
  86                 "stdio"  // General I/O, both disk and network
  87                 " rpath" // Read files and directories
  88                 " wpath" // Write files and directories
  89                 " cpath" // Create new ones
  90                 " dns"   // Resolve domain names
  91                 " inet"  // Make network connections
  92                 " unix"; // Control socket connections from tinc CLI
  93
  94         if(can_exec) {
  95                 // fork() and execve() for scripts and exec proxies
  96                 const char *exec = " proc exec";
  97                 size_t n = strlcat(promises, exec, sizeof(promises));
  98                 assert(n < sizeof(promises));
  99         }
 100
 101         return restrict_privs(promises, can_exec ? PROMISES_ALL : PROMISES_NONE);
 102 }
 103
 104 static void sandbox_paths(bool can_exec) {
 105         if(chrooted()) {
 106                 logger(DEBUG_ALWAYS, LOG_DEBUG, "chroot is used. Disabling path sandbox.");
 107                 return;
 108         }
 109
 110         open_common_paths(can_exec);
 111         can_use_new_paths = false;
 112
 113         if(can_exec) {
 114                 if(proxytype == PROXY_EXEC && !access(proxyhost, X_OK)) {
 115                         logger(DEBUG_ALWAYS, LOG_WARNING, "Looks like a shell expression was used for exec proxy. Using weak path sandbox.");
 116                         allow_path("/", "rx");
 117                 } else {
 118                         open_exec_paths();
 119                 }
 120         }
 121 }
 122
 123 static bool sandbox_can_after_enter(sandbox_action_t action) {
 124         switch(action) {
 125         case START_PROCESSES:
 126                 return current_level < SANDBOX_HIGH;
 127
 128         case USE_NEW_PATHS:
 129                 return can_use_new_paths;
 130
 131         default:
 132                 abort();
 133         }
 134 }
 135
 136 bool sandbox_can(sandbox_action_t action, sandbox_time_t when) {
 137         if(when == AFTER_SANDBOX || entered) {
 138                 return sandbox_can_after_enter(action);
 139         } else {
 140                 return true;
 141         }
 142 }
 143
 144 void sandbox_set_level(sandbox_level_t level) {
 145         assert(!entered);
 146         current_level = level;
 147 }
 148
 149 bool sandbox_enter() {
 150         assert(!entered);
 151         entered = true;
 152
 153         if(current_level == SANDBOX_NONE) {
 154                 logger(DEBUG_ALWAYS, LOG_DEBUG, "Sandbox is disabled");
 155                 return true;
 156         }
 157
 158         bool can_exec = sandbox_can_after_enter(START_PROCESSES);
 159
 160         sandbox_paths(can_exec);
 161
 162         if(sandbox_privs(can_exec)) {
 163                 logger(DEBUG_ALWAYS, LOG_DEBUG, "Entered sandbox at level %d", current_level);
 164                 return true;
 165         }
 166
 167         logger(DEBUG_ALWAYS, LOG_ERR, "Could not enter sandbox. Set a lower level or disable it in tinc.conf");
 168         current_level = SANDBOX_NONE;
 169
 170         return false;
 171 }