tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
Log | Files | Refs | README | LICENSE

SandboxHooks.cpp (3317B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
      5 * You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #include "mozilla/Assertions.h"
      8 #include "mozilla/Atomics.h"
      9 #include "mozilla/Types.h"
     10 
     11 #include <dlfcn.h>
     12 #include <signal.h>
     13 #include <errno.h>
     14 #include <stdio.h>
     15 #include <sys/inotify.h>
     16 #ifdef MOZ_X11
     17 #  include <X11/Xlib.h>
     18 #endif
     19 
     20 // Signal number used to enable seccomp on each thread.
     21 extern mozilla::Atomic<int> gSeccompTsyncBroadcastSignum;
     22 
     23 static bool SigSetNeedsFixup(const sigset_t* aSet) {
     24  int tsyncSignum = gSeccompTsyncBroadcastSignum;
     25 
     26  return aSet != nullptr &&
     27         (sigismember(aSet, SIGSYS) ||
     28          (tsyncSignum != 0 && sigismember(aSet, tsyncSignum)));
     29 }
     30 
     31 static void SigSetFixup(sigset_t* aSet) {
     32  int tsyncSignum = gSeccompTsyncBroadcastSignum;
     33  int rv = sigdelset(aSet, SIGSYS);
     34  MOZ_RELEASE_ASSERT(rv == 0);
     35  if (tsyncSignum != 0) {
     36    rv = sigdelset(aSet, tsyncSignum);
     37    MOZ_RELEASE_ASSERT(rv == 0);
     38  }
     39 }
     40 
     41 // This file defines a hook for sigprocmask() and pthread_sigmask().
     42 // Bug 1176099: some threads block SIGSYS signal which breaks our seccomp-bpf
     43 // sandbox. To avoid this, we intercept the call and remove SIGSYS.
     44 //
     45 // ENOSYS indicates an error within the hook function itself.
     46 static int HandleSigset(int (*aRealFunc)(int, const sigset_t*, sigset_t*),
     47                        int aHow, const sigset_t* aSet, sigset_t* aOldSet,
     48                        bool aUseErrno) {
     49  if (!aRealFunc) {
     50    if (aUseErrno) {
     51      errno = ENOSYS;
     52      return -1;
     53    }
     54 
     55    return ENOSYS;
     56  }
     57 
     58  // Avoid unnecessary work
     59  if (aHow == SIG_UNBLOCK || !SigSetNeedsFixup(aSet)) {
     60    return aRealFunc(aHow, aSet, aOldSet);
     61  }
     62 
     63  sigset_t newSet = *aSet;
     64  SigSetFixup(&newSet);
     65  return aRealFunc(aHow, &newSet, aOldSet);
     66 }
     67 
     68 extern "C" MOZ_EXPORT int sigprocmask(int how, const sigset_t* set,
     69                                      sigset_t* oldset) {
     70  static auto sRealFunc =
     71      (int (*)(int, const sigset_t*, sigset_t*))dlsym(RTLD_NEXT, "sigprocmask");
     72 
     73  return HandleSigset(sRealFunc, how, set, oldset, true);
     74 }
     75 
     76 extern "C" MOZ_EXPORT int pthread_sigmask(int how, const sigset_t* set,
     77                                          sigset_t* oldset) {
     78  static auto sRealFunc = (int (*)(int, const sigset_t*, sigset_t*))dlsym(
     79      RTLD_NEXT, "pthread_sigmask");
     80 
     81  return HandleSigset(sRealFunc, how, set, oldset, false);
     82 }
     83 
     84 extern "C" MOZ_EXPORT int sigaction(int signum, const struct sigaction* act,
     85                                    struct sigaction* oldact) {
     86  static auto sRealFunc =
     87      (int (*)(int, const struct sigaction*, struct sigaction*))dlsym(
     88          RTLD_NEXT, "sigaction");
     89 
     90  if (!sRealFunc) {
     91    errno = ENOSYS;
     92    return -1;
     93  }
     94 
     95  if (act == nullptr || !SigSetNeedsFixup(&act->sa_mask)) {
     96    return sRealFunc(signum, act, oldact);
     97  }
     98 
     99  struct sigaction newact = *act;
    100  SigSetFixup(&newact.sa_mask);
    101  return sRealFunc(signum, &newact, oldact);
    102 }
    103 
    104 extern "C" MOZ_EXPORT int inotify_init(void) { return inotify_init1(0); }
    105 
    106 extern "C" MOZ_EXPORT int inotify_init1(int flags) {
    107  errno = ENOSYS;
    108  return -1;
    109 }