diff --git a/security/sandbox/linux/SandboxBrokerClient.cpp b/security/sandbox/linux/SandboxBrokerClient.cpp
new file mode 100644
index 00000000000..c6d4ebf08f6
--- /dev/null
+++ b/security/sandbox/linux/SandboxBrokerClient.cpp
@@ -0,0 +1,181 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SandboxBrokerClient.h"
+#include "SandboxInfo.h"
+#include "SandboxLogging.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/NullPtr.h"
+#include "base/strings/safe_sprintf.h"
+
+namespace mozilla {
+
+SandboxBrokerClient::SandboxBrokerClient(int aFd)
+: mFileDesc(aFd)
+{
+}
+
+SandboxBrokerClient::~SandboxBrokerClient()
+{
+  close(mFileDesc);
+}
+
+int
+SandboxBrokerClient::DoCall(const Request* aReq, const char* aPath,
+                            struct stat* aStat, bool expectFd)
+{
+  // Remap /proc/self to the actual pid, so that the broker can open
+  // it.  This happens here instead of in the broker to follow the
+  // principle of least privilege and keep the broker as simple as
+  // possible.  (Note: when pid namespaces happen, this will also need
+  // to remap the inner pid to the outer pid.)
+  static const char kProcSelf[] = "/proc/self/";
+  static const size_t kProcSelfLen = sizeof(kProcSelf) - 1;
+  const char* path = aPath;
+  // This buffer just needs to be large enough for any such path that
+  // the policy would actually allow.  sizeof("/proc/2147483647/") == 18.
+  char rewrittenPath[64];
+  if (strncmp(aPath, kProcSelf, kProcSelfLen) == 0) {
+    ssize_t len =
+      base::strings::SafeSPrintf(rewrittenPath, "/proc/%d/%s",
+                                 getpid(), aPath + kProcSelfLen);
+    if (static_cast<size_t>(len) < sizeof(rewrittenPath)) {
+      if (SandboxInfo::Get().Test(SandboxInfo::kVerbose)) {
+        SANDBOX_LOG_ERROR("rewriting %s -> %s", aPath, rewrittenPath);
+      }
+      path = rewrittenPath;
+    } else {
+      SANDBOX_LOG_ERROR("not rewriting unexpectedly long path %s", aPath);
+    }
+  }
+
+  struct iovec ios[2];
+  int respFds[2];
+
+  // Set up iovecs for request + path.
+  ios[0].iov_base = const_cast<Request*>(aReq);
+  ios[0].iov_len = sizeof(*aReq);
+  ios[1].iov_base = const_cast<char*>(path);
+  ios[1].iov_len = strlen(path);
+  if (ios[1].iov_len > kMaxPathLen) {
+    return -ENAMETOOLONG;
+  }
+
+  // Create response socket and send request.
+  if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, respFds) < 0) {
+    return -errno;
+  }
+  const ssize_t sent = SendWithFd(mFileDesc, ios, 2, respFds[1]);
+  const int sendErrno = errno;
+  MOZ_ASSERT(sent < 0 ||
+	     static_cast<size_t>(sent) == ios[0].iov_len + ios[1].iov_len);
+  close(respFds[1]);
+  if (sent < 0) {
+    close(respFds[0]);
+    return -sendErrno;
+  }
+
+  // Set up iovecs for response.
+  Response resp;
+  ios[0].iov_base = &resp;
+  ios[0].iov_len = sizeof(resp);
+  if (aStat) {
+    ios[1].iov_base = aStat;
+    ios[1].iov_len = sizeof(*aStat);
+  } else {
+    ios[1].iov_base = nullptr;
+    ios[1].iov_len = 0;
+  }
+
+  // Wait for response and return appropriately.
+  int openedFd = -1;
+  const ssize_t recvd = RecvWithFd(respFds[0], ios, aStat ? 2 : 1,
+                                   expectFd ? &openedFd : nullptr);
+  const int recvErrno = errno;
+  close(respFds[0]);
+  if (recvd < 0) {
+    return -recvErrno;
+  }
+  if (recvd == 0) {
+    SANDBOX_LOG_ERROR("Unexpected EOF, op %d flags 0%o path %s",
+                      aReq->mOp, aReq->mFlags, path);
+    return -EIO;
+  }
+  if (resp.mError != 0) {
+    // If the operation fails, the return payload will be empty;
+    // adjust the iov_len for the following assertion.
+    ios[1].iov_len = 0;
+  }
+  MOZ_ASSERT(static_cast<size_t>(recvd) == ios[0].iov_len + ios[1].iov_len);
+  if (resp.mError == 0) {
+    // Success!
+    if (expectFd) {
+      MOZ_ASSERT(openedFd >= 0);
+      return openedFd;
+    }
+    return 0;
+  }
+  if (SandboxInfo::Get().Test(SandboxInfo::kVerbose)) {
+    // Keep in mind that "rejected" files can include ones that don't
+    // actually exist, if it's something that's optional or part of a
+    // search path (e.g., shared libraries).  In those cases, this
+    // error message is expected.
+    SANDBOX_LOG_ERROR("Rejected errno %d op %d flags 0%o path %s",
+                      resp.mError, aReq->mOp, aReq->mFlags, path);
+  }
+  if (openedFd >= 0) {
+    close(openedFd);
+  }
+  return -resp.mError;
+}
+
+int
+SandboxBrokerClient::Open(const char* aPath, int aFlags)
+{
+  Request req = { SANDBOX_FILE_OPEN, aFlags };
+  int maybeFd = DoCall(&req, aPath, nullptr, true);
+  if (maybeFd >= 0) {
+    // NSPR has opinions about file flags.  Fix O_CLOEXEC.
+    if ((aFlags & O_CLOEXEC) == 0) {
+      fcntl(maybeFd, F_SETFD, 0);
+    }
+  }
+  return maybeFd;
+}
+
+int
+SandboxBrokerClient::Access(const char* aPath, int aMode)
+{
+  Request req = { SANDBOX_FILE_ACCESS, aMode };
+  return DoCall(&req, aPath, nullptr, false);
+}
+
+int
+SandboxBrokerClient::Stat(const char* aPath, struct stat* aStat)
+{
+  Request req = { SANDBOX_FILE_STAT, 0 };
+  return DoCall(&req, aPath, aStat, false);
+}
+
+int
+SandboxBrokerClient::LStat(const char* aPath, struct stat* aStat)
+{
+  Request req = { SANDBOX_FILE_STAT, O_NOFOLLOW };
+  return DoCall(&req, aPath, aStat, false);
+}
+
+} // namespace mozilla
+
diff --git a/security/sandbox/linux/SandboxBrokerClient.h b/security/sandbox/linux/SandboxBrokerClient.h
new file mode 100644
index 00000000000..9a1ff9e6d71
--- /dev/null
+++ b/security/sandbox/linux/SandboxBrokerClient.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_SandboxBrokerClient_h
+#define mozilla_SandboxBrokerClient_h
+
+#include "broker/SandboxBrokerCommon.h"
+
+#include "mozilla/Attributes.h"
+
+// This is the client for the sandbox broker described in
+// broker/SandboxBroker.h; its constructor takes the file descriptor
+// returned by SandboxBroker::Create, passed to the child over IPC.
+//
+// The operations exposed here can be called from any thread and in
+// async signal handlers, like the corresponding system calls.  The
+// intended use is from a seccomp-bpf SIGSYS handler, to transparently
+// replace those syscalls, but they could also be used directly.
+
+struct stat;
+
+namespace mozilla {
+
+class SandboxBrokerClient final : private SandboxBrokerCommon {
+ public:
+  explicit SandboxBrokerClient(int aFd);
+  ~SandboxBrokerClient();
+
+  int Open(const char* aPath, int aFlags);
+  int Access(const char* aPath, int aMode);
+  int Stat(const char* aPath, struct stat* aStat);
+  int LStat(const char* aPath, struct stat* aStat);
+
+ private:
+  int mFileDesc;
+
+  int DoCall(const Request* aReq, const char* aPath, struct stat* aStat,
+             bool expectFd);
+};
+
+} // namespace mozilla
+
+#endif // mozilla_SandboxBrokerClient_h
diff --git a/security/sandbox/linux/broker/SandboxBroker.cpp b/security/sandbox/linux/broker/SandboxBroker.cpp
new file mode 100644
index 00000000000..a465e33ff50
--- /dev/null
+++ b/security/sandbox/linux/broker/SandboxBroker.cpp
@@ -0,0 +1,404 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SandboxBroker.h"
+#include "SandboxInfo.h"
+#include "SandboxLogging.h"
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifdef XP_LINUX
+#include <sys/prctl.h>
+#endif
+
+#ifdef MOZ_WIDGET_GONK
+#include <private/android_filesystem_config.h>
+#include <sys/syscall.h>
+#endif
+
+#include "mozilla/Assertions.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Move.h"
+#include "mozilla/NullPtr.h"
+#include "mozilla/ipc/FileDescriptor.h"
+
+namespace mozilla {
+
+// This constructor signals failure by setting mFileDesc and aClientFd to -1.
+SandboxBroker::SandboxBroker(UniquePtr<const Policy> aPolicy, int aChildPid,
+                             int& aClientFd)
+  : mChildPid(aChildPid), mPolicy(Move(aPolicy))
+{
+  int fds[2];
+  if (0 != socketpair(AF_UNIX, SOCK_SEQPACKET, 0, fds)) {
+    SANDBOX_LOG_ERROR("SandboxBroker: socketpair failed: %s", strerror(errno));
+    mFileDesc = -1;
+    aClientFd = -1;
+    return;
+  }
+  mFileDesc = fds[0];
+  aClientFd = fds[1];
+
+  if (!PlatformThread::Create(0, this, &mThread)) {
+    SANDBOX_LOG_ERROR("SandboxBroker: thread creation failed: %s",
+                      strerror(errno));
+    close(mFileDesc);
+    close(aClientFd);
+    mFileDesc = -1;
+    aClientFd = -1;
+  }
+}
+
+UniquePtr<SandboxBroker>
+SandboxBroker::Create(UniquePtr<const Policy> aPolicy, int aChildPid,
+                      ipc::FileDescriptor& aClientFdOut)
+{
+  int clientFd;
+  // Can't use MakeUnique here because the constructor is private.
+  UniquePtr<SandboxBroker> rv(new SandboxBroker(Move(aPolicy), aChildPid,
+                                                clientFd));
+  if (clientFd < 0) {
+    rv = nullptr;
+  } else {
+    aClientFdOut = ipc::FileDescriptor(clientFd);
+  }
+  return Move(rv);
+}
+
+SandboxBroker::~SandboxBroker() {
+  // If the constructor failed, there's nothing to be done here.
+  if (mFileDesc < 0) {
+    return;
+  }
+
+  shutdown(mFileDesc, SHUT_RD);
+  // The thread will now get EOF even if the client hasn't exited.
+  PlatformThread::Join(mThread);
+  // Now that the thread has exited, the fd will no longer be accessed.
+  close(mFileDesc);
+  // Having ensured that this object outlives the thread, this
+  // destructor can now return.
+}
+
+SandboxBroker::Policy::Policy() { }
+SandboxBroker::Policy::~Policy() { }
+
+SandboxBroker::Policy::Policy(const Policy& aOther) {
+  for (auto iter = aOther.mMap.ConstIter(); !iter.Done(); iter.Next()) {
+    mMap.Put(iter.Key(), iter.Data());
+  }
+}
+
+void
+SandboxBroker::Policy::AddPath(int aPerms, const char* aPath,
+                               AddCondition aCond)
+{
+  nsDependentCString path(aPath);
+  MOZ_ASSERT(path.Length() <= kMaxPathLen);
+  int perms;
+  if (aCond == AddIfExistsNow) {
+    struct stat statBuf;
+    if (lstat(aPath, &statBuf) != 0) {
+      return;
+    }
+  }
+  if (!mMap.Get(path, &perms)) {
+    perms = MAY_ACCESS;
+  } else {
+    MOZ_ASSERT(perms & MAY_ACCESS);
+  }
+  if (SandboxInfo::Get().Test(SandboxInfo::kVerbose)) {
+    SANDBOX_LOG_ERROR("policy for %s: %d -> %d", aPath, perms, perms | aPerms);
+  }
+  perms |= aPerms;
+  mMap.Put(path, perms);
+}
+
+void
+SandboxBroker::Policy::AddTree(int aPerms, const char* aPath)
+{
+  struct stat statBuf;
+
+  if (stat(aPath, &statBuf) != 0) {
+    return;
+  }
+  if (!S_ISDIR(statBuf.st_mode)) {
+    AddPath(aPerms, aPath, AddAlways);
+  } else {
+    DIR* dirp = opendir(aPath);
+    if (!dirp) {
+      return;
+    }
+    while (struct dirent* de = readdir(dirp)) {
+      if (strcmp(de->d_name, ".") == 0 || strcmp(de->d_name, "..") == 0) {
+        continue;
+      }
+      // Note: could optimize the string handling.
+      nsAutoCString subPath;
+      subPath.Assign(aPath);
+      subPath.Append('/');
+      subPath.Append(de->d_name);
+      AddTree(aPerms, subPath.get());
+    }
+    closedir(dirp);
+  }
+}
+
+void
+SandboxBroker::Policy::AddPrefix(int aPerms, const char* aDir,
+                                 const char* aPrefix)
+{
+  size_t prefixLen = strlen(aPrefix);
+  DIR* dirp = opendir(aDir);
+  struct dirent* de;
+  if (!dirp) {
+    return;
+  }
+  while ((de = readdir(dirp))) {
+    if (strncmp(de->d_name, aPrefix, prefixLen) == 0) {
+      nsAutoCString subPath;
+      subPath.Assign(aDir);
+      subPath.Append('/');
+      subPath.Append(de->d_name);
+      AddPath(aPerms, subPath.get(), AddAlways);
+    }
+  }
+  closedir(dirp);
+}
+
+int
+SandboxBroker::Policy::Lookup(const nsACString& aPath) const
+{
+  return mMap.Get(aPath);
+}
+
+static bool
+AllowAccess(int aReqFlags, int aPerms)
+{
+  if (aReqFlags & ~(R_OK|W_OK|F_OK)) {
+    return false;
+  }
+  int needed = 0;
+  if (aReqFlags & R_OK) {
+    needed |= SandboxBroker::MAY_READ;
+  }
+  if (aReqFlags & W_OK) {
+    needed |= SandboxBroker::MAY_WRITE;
+  }
+  return (aPerms & needed) == needed;
+}
+
+// These flags are added to all opens to prevent possible side-effects
+// on this process.  These shouldn't be relevant to the child process
+// in any case due to the sandboxing restrictions on it.  (See also
+// the use of MSG_CMSG_CLOEXEC in SandboxBrokerCommon.cpp).
+static const int kRequiredOpenFlags = O_CLOEXEC | O_NOCTTY;
+
+// Linux originally assigned a flag bit to O_SYNC but implemented the
+// semantics standardized as O_DSYNC; later, that bit was renamed and
+// a new bit was assigned to the full O_SYNC, and O_SYNC was redefined
+// to be both bits.  As a result, this #define is needed to compensate
+// for outdated kernel headers like Android's.
+#define O_SYNC_NEW 04010000
+static const int kAllowedOpenFlags =
+  O_APPEND | O_ASYNC | O_DIRECT | O_DIRECTORY | O_EXCL | O_LARGEFILE
+  | O_NOATIME | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK | O_NDELAY | O_SYNC_NEW
+  | O_TRUNC | O_CLOEXEC | O_CREAT;
+#undef O_SYNC_NEW
+
+static bool
+AllowOpen(int aReqFlags, int aPerms)
+{
+  if (aReqFlags & ~O_ACCMODE & ~kAllowedOpenFlags) {
+    return false;
+  }
+  int needed;
+  switch(aReqFlags & O_ACCMODE) {
+  case O_RDONLY:
+    needed = SandboxBroker::MAY_READ;
+    break;
+  case O_WRONLY:
+    needed = SandboxBroker::MAY_WRITE;
+    break;
+  case O_RDWR:
+    needed = SandboxBroker::MAY_READ | SandboxBroker::MAY_WRITE;
+    break;
+  default:
+    return false;
+  }
+  if (aReqFlags & O_CREAT) {
+    needed |= SandboxBroker::MAY_CREATE;
+  }
+  return (aPerms & needed) == needed;
+}
+
+static int
+DoStat(const char* aPath, struct stat* aStat, int aFlags)
+{
+  if (aFlags & O_NOFOLLOW) {
+    return lstat(aPath, aStat);
+  }
+  return stat(aPath, aStat);
+}
+
+void
+SandboxBroker::ThreadMain(void)
+{
+  char threadName[16];
+  snprintf(threadName, sizeof(threadName), "FS Broker %d", mChildPid);
+  PlatformThread::SetName(threadName);
+
+#ifdef MOZ_WIDGET_GONK
+#ifdef __NR_setreuid32
+  static const long nr_setreuid = __NR_setreuid32;
+  static const long nr_setregid = __NR_setregid32;
+#else
+  static const long nr_setreuid = __NR_setreuid;
+  static const long nr_setregid = __NR_setregid;
+#endif
+  if (syscall(nr_setregid, getgid(), AID_APP + mChildPid) != 0 ||
+      syscall(nr_setreuid, getuid(), AID_APP + mChildPid) != 0) {
+    MOZ_CRASH("SandboxBroker: failed to drop privileges");
+  }
+#endif
+
+  while (true) {
+    struct iovec ios[2];
+    char pathBuf[kMaxPathLen + 1];
+    size_t pathLen;
+    struct stat statBuf;
+    Request req;
+    Response resp;
+    int respfd;
+
+    ios[0].iov_base = &req;
+    ios[0].iov_len = sizeof(req);
+    ios[1].iov_base = pathBuf;
+    ios[1].iov_len = kMaxPathLen;
+
+    const ssize_t recvd = RecvWithFd(mFileDesc, ios, 2, &respfd);
+    if (recvd == 0) {
+      if (SandboxInfo::Get().Test(SandboxInfo::kVerbose)) {
+        SANDBOX_LOG_ERROR("EOF from pid %d", mChildPid);
+      }
+      break;
+    }
+    // It could be possible to continue after errors and short reads,
+    // at least in some cases, but protocol violation indicates a
+    // hostile client, so terminate the broker instead.
+    if (recvd < 0) {
+      SANDBOX_LOG_ERROR("bad read from pid %d: %s",
+                        mChildPid, strerror(errno));
+      shutdown(mFileDesc, SHUT_RD);
+      break;
+    }
+    if (recvd < static_cast<ssize_t>(sizeof(req))) {
+      SANDBOX_LOG_ERROR("bad read from pid %d (%d < %d)",
+                        mChildPid, recvd, sizeof(req));
+      shutdown(mFileDesc, SHUT_RD);
+      break;
+    }
+    if (respfd == -1) {
+      SANDBOX_LOG_ERROR("no response fd from pid %d", mChildPid);
+      shutdown(mFileDesc, SHUT_RD);
+      break;
+    }
+
+    // Initialize the response with the default failure.
+    memset(&resp, 0, sizeof(resp));
+    memset(&statBuf, 0, sizeof(statBuf));
+    resp.mError = EACCES;
+    ios[0].iov_base = &resp;
+    ios[0].iov_len = sizeof(resp);
+    ios[1].iov_base = nullptr;
+    ios[1].iov_len = 0;
+    int openedFd = -1;
+
+    // Look up the pathname.
+    pathLen = recvd - sizeof(req);
+    // It shouldn't be possible for recvmsg to violate this assertion,
+    // but one more predictable branch shouldn't have much perf impact:
+    MOZ_RELEASE_ASSERT(pathLen <= kMaxPathLen);
+    pathBuf[pathLen] = '\0';
+    int perms = 0;
+    if (!memchr(pathBuf, '\0', pathLen)) {
+      perms = mPolicy->Lookup(nsDependentCString(pathBuf, pathLen));
+    }
+
+    // And now perform the operation if allowed.
+    if (perms & CRASH_INSTEAD) {
+      // This is somewhat nonmodular, but it works.
+      resp.mError = ENOSYS;
+    } else if (perms & MAY_ACCESS) {
+      switch(req.mOp) {
+      case SANDBOX_FILE_OPEN:
+        if (AllowOpen(req.mFlags, perms)) {
+          // Permissions for O_CREAT hardwired to 0600; if that's
+          // ever a problem we can change the protocol (but really we
+          // should be trying to remove uses of MAY_CREATE, not add
+          // new ones).
+          openedFd = open(pathBuf, req.mFlags | kRequiredOpenFlags, 0600);
+          if (openedFd >= 0) {
+            resp.mError = 0;
+          } else {
+            resp.mError = errno;
+          }
+        }
+        break;
+
+      case SANDBOX_FILE_ACCESS:
+        if (AllowAccess(req.mFlags, perms)) {
+          // This can't use access() itself because that uses the ruid
+          // and not the euid.  In theory faccessat() with AT_EACCESS
+          // would work, but Linux doesn't actually implement the
+          // flags != 0 case; glibc has a hack which doesn't even work
+          // in this case so it'll ignore the flag, and Bionic just
+          // passes through the syscall and always ignores the flags.
+          //
+          // Instead, because we've already checked the requested
+          // r/w/x bits against the policy, just return success if the
+          // file exists and hope that's close enough.
+          if (stat(pathBuf, &statBuf) == 0) {
+            resp.mError = 0;
+          } else {
+            resp.mError = errno;
+          }
+        }
+        break;
+
+      case SANDBOX_FILE_STAT:
+        if (DoStat(pathBuf, &statBuf, req.mFlags) == 0) {
+          resp.mError = 0;
+          ios[1].iov_base = &statBuf;
+          ios[1].iov_len = sizeof(statBuf);
+        } else {
+          resp.mError = errno;
+        }
+        break;
+      }
+    } else {
+      MOZ_ASSERT(perms == 0);
+    }
+
+    const size_t numIO = ios[1].iov_len > 0 ? 2 : 1;
+    DebugOnly<const ssize_t> sent = SendWithFd(respfd, ios, numIO, openedFd);
+    close(respfd);
+    MOZ_ASSERT(sent < 0 ||
+               static_cast<size_t>(sent) == ios[0].iov_len + ios[1].iov_len);
+
+    if (openedFd >= 0) {
+      close(openedFd);
+    }
+  }
+}
+
+} // namespace mozilla
diff --git a/security/sandbox/linux/broker/SandboxBroker.h b/security/sandbox/linux/broker/SandboxBroker.h
new file mode 100644
index 00000000000..0e78d43557d
--- /dev/null
+++ b/security/sandbox/linux/broker/SandboxBroker.h
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_SandboxBroker_h
+#define mozilla_SandboxBroker_h
+
+#include "mozilla/SandboxBrokerCommon.h"
+
+#include "base/platform_thread.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/UniquePtr.h"
+#include "nsDataHashtable.h"
+#include "nsHashKeys.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+namespace ipc {
+class FileDescriptor;
+}
+
+// This class implements a broker for filesystem operations requested
+// by a sandboxed child process -- opening files and accessing their
+// metadata.  (This is necessary in order to restrict access by path;
+// seccomp-bpf can filter only on argument register values, not
+// parameters passed in memory like pathnames.)
+//
+// The policy is currently just a map from strings to sets of
+// permissions; the broker doesn't attempt to interpret or
+// canonicalize pathnames.  This makes the broker simpler, and thus
+// less likely to contain vulnerabilities a compromised client could
+// exploit.  (This might need to change in the future if we need to
+// whitelist a set of files that could change after policy
+// construction, like hotpluggable devices.)
+//
+// The broker currently runs on a thread in the parent process (with
+// effective uid changed on B2G), which is for memory efficiency
+// (compared to forking a process) and simplicity (compared to having
+// a separate executable and serializing/deserializing the policy).
+//
+// See also ../SandboxBrokerClient.h for the corresponding client.
+
+class SandboxBroker final
+  : private SandboxBrokerCommon
+  , public PlatformThread::Delegate
+{
+ public:
+  enum Perms {
+    MAY_ACCESS = 1 << 0,
+    MAY_READ = 1 << 1,
+    MAY_WRITE = 1 << 2,
+    MAY_CREATE = 1 << 3,
+    // This flag is for testing policy changes -- when the client is
+    // used with the seccomp-bpf integration, an access to this file
+    // will invoke a crash dump with the context of the syscall.
+    // (This overrides all other flags.)
+    CRASH_INSTEAD = 1 << 4,
+  };
+  // Bitwise operations on enum values return ints, so just use int in
+  // the hash table type (and below) to avoid cluttering code with casts.
+  typedef nsDataHashtable<nsCStringHashKey, int> PathMap;
+
+  class Policy {
+    PathMap mMap;
+  public:
+    Policy();
+    Policy(const Policy& aOther);
+    ~Policy();
+
+    enum AddCondition {
+      AddIfExistsNow,
+      AddAlways,
+    };
+    // Typically, files that don't exist at policy creation time don't
+    // need to be whitelisted, but this allows adding entries for
+    // them if they'll exist later.  See also the overload below.
+    void AddPath(int aPerms, const char* aPath, AddCondition aCond);
+    // This adds all regular files (not directories) in the tree
+    // rooted at the given path.
+    void AddTree(int aPerms, const char* aPath);
+    // All files in a directory with a given prefix; useful for devices.
+    void AddPrefix(int aPerms, const char* aDir, const char* aPrefix);
+    // Default: add file if it exists when creating policy or if we're
+    // conferring permission to create it (log files, etc.).
+    void AddPath(int aPerms, const char* aPath) {
+      AddPath(aPerms, aPath,
+              (aPerms & MAY_CREATE) ? AddAlways : AddIfExistsNow);
+    }
+    int Lookup(const nsACString& aPath) const;
+    int Lookup(const char* aPath) const {
+      return Lookup(nsDependentCString(aPath));
+    }
+  };
+
+  // Constructing a broker involves creating a socketpair and a
+  // background thread to handle requests, so it can fail.  If this
+  // returns nullptr, do not use the value of aClientFdOut.
+  static UniquePtr<SandboxBroker>
+    Create(UniquePtr<const Policy> aPolicy, int aChildPid,
+           ipc::FileDescriptor& aClientFdOut);
+  virtual ~SandboxBroker();
+
+ private:
+  PlatformThreadHandle mThread;
+  int mFileDesc;
+  const int mChildPid;
+  const UniquePtr<const Policy> mPolicy;
+
+  SandboxBroker(UniquePtr<const Policy> aPolicy, int aChildPid,
+                int& aClientFd);
+  void ThreadMain(void) override;
+
+  // Holding a UniquePtr should disallow copying, but to make that explicit:
+  SandboxBroker(const SandboxBroker&) = delete;
+  void operator=(const SandboxBroker&) = delete;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_SandboxBroker_h
diff --git a/security/sandbox/linux/broker/SandboxBrokerCommon.cpp b/security/sandbox/linux/broker/SandboxBrokerCommon.cpp
new file mode 100644
index 00000000000..fe7bc8c45b0
--- /dev/null
+++ b/security/sandbox/linux/broker/SandboxBrokerCommon.cpp
@@ -0,0 +1,120 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SandboxBrokerCommon.h"
+
+#include "mozilla/Assertions.h"
+
+#include <errno.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifndef MSG_CMSG_CLOEXEC
+#ifdef XP_LINUX
+// As always, Android's kernel headers are somewhat old.
+#define MSG_CMSG_CLOEXEC 0x40000000
+#else
+// Most of this code can support other POSIX OSes, but being able to
+// receive fds and atomically make them close-on-exec is important,
+// because this is running in a multithreaded process that can fork.
+// In the future, if the broker becomes a dedicated executable, this
+// can change.
+#error "No MSG_CMSG_CLOEXEC?"
+#endif // XP_LINUX
+#endif // MSG_CMSG_CLOEXEC
+
+namespace mozilla {
+
+/* static */ ssize_t
+SandboxBrokerCommon::RecvWithFd(int aFd, const iovec* aIO, size_t aNumIO,
+                                    int* aPassedFdPtr)
+{
+  struct msghdr msg = {};
+  msg.msg_iov = const_cast<iovec*>(aIO);
+  msg.msg_iovlen = aNumIO;
+
+  char cmsg_buf[CMSG_SPACE(sizeof(int))];
+  if (aPassedFdPtr) {
+    msg.msg_control = cmsg_buf;
+    msg.msg_controllen = sizeof(cmsg_buf);
+    *aPassedFdPtr = -1;
+  }
+
+  ssize_t rv;
+  do {
+    // MSG_CMSG_CLOEXEC is needed to prevent the parent process from
+    // accidentally leaking a copy of the child's response socket to a
+    // new child process.  (The child won't be able to exec, so this
+    // doesn't matter as much for that direction.)
+    rv = recvmsg(aFd, &msg, MSG_CMSG_CLOEXEC);
+  } while (rv < 0 && errno == EINTR);
+
+  if (rv <= 0) {
+    return rv;
+  }
+  if (msg.msg_controllen > 0) {
+    MOZ_ASSERT(aPassedFdPtr);
+    struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
+    if (cmsg->cmsg_level == SOL_SOCKET &&
+        cmsg->cmsg_type == SCM_RIGHTS) {
+      int* fds = reinterpret_cast<int*>(CMSG_DATA(cmsg));
+      if (cmsg->cmsg_len != CMSG_LEN(sizeof(int))) {
+        // A client could, for example, send an extra 32-bit int if
+        // CMSG_SPACE pads to 64-bit size_t alignment.  If so, treat
+        // it as an error, but also don't leak the fds.
+        for (size_t i = 0; CMSG_LEN(sizeof(int) * i) < cmsg->cmsg_len; ++i) {
+          close(fds[i]);
+        }
+        errno = EMSGSIZE;
+        return -1;
+      }
+      *aPassedFdPtr = fds[0];
+    } else {
+      errno = EPROTO;
+      return -1;
+    }
+  }
+  if (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC)) {
+    if (aPassedFdPtr && *aPassedFdPtr >= 0) {
+      close(*aPassedFdPtr);
+      *aPassedFdPtr = -1;
+    }
+    errno = EMSGSIZE;
+    return -1;
+  }
+
+  return rv;
+}
+
+/* static */ ssize_t
+SandboxBrokerCommon::SendWithFd(int aFd, const iovec* aIO, size_t aNumIO,
+                                    int aPassedFd)
+{
+  struct msghdr msg = {};
+  msg.msg_iov = const_cast<iovec*>(aIO);
+  msg.msg_iovlen = aNumIO;
+
+  char cmsg_buf[CMSG_SPACE(sizeof(int))];
+  if (aPassedFd != -1) {
+    msg.msg_control = cmsg_buf;
+    msg.msg_controllen = sizeof(cmsg_buf);
+    struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
+    cmsg->cmsg_level = SOL_SOCKET;
+    cmsg->cmsg_type = SCM_RIGHTS;
+    cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+    *reinterpret_cast<int*>(CMSG_DATA(cmsg)) = aPassedFd;
+  }
+
+  ssize_t rv;
+  do {
+    rv = sendmsg(aFd, &msg, MSG_NOSIGNAL);
+  } while (rv < 0 && errno == EINTR);
+
+  return rv;
+}
+
+} // namespace mozilla
diff --git a/security/sandbox/linux/broker/SandboxBrokerCommon.h b/security/sandbox/linux/broker/SandboxBrokerCommon.h
new file mode 100644
index 00000000000..e52b8b45f45
--- /dev/null
+++ b/security/sandbox/linux/broker/SandboxBrokerCommon.h
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_SandboxBrokerTypes_h
+#define mozilla_SandboxBrokerTypes_h
+
+#include <sys/types.h>
+
+struct iovec;
+
+// This file defines the protocol between the filesystem broker,
+// described in SandboxBroker.h, and its client, described in
+// ../SandboxBrokerClient.h; and it defines some utility functions
+// used by both.
+//
+// In order to keep the client simple while allowing it to be thread
+// safe and async signal safe, the main broker socket is used only for
+// requests; responses arrive on a per-request socketpair sent with
+// the request.  (This technique is also used by Chromium and Breakpad.)
+
+namespace mozilla {
+
+class SandboxBrokerCommon {
+public:
+  enum Operation {
+    SANDBOX_FILE_OPEN,
+    SANDBOX_FILE_ACCESS,
+    SANDBOX_FILE_STAT,
+  };
+
+  struct Request {
+    Operation mOp;
+    // For open, flags; for access, "mode"; for stat, O_NOFOLLOW for lstat.
+    int mFlags;
+    // The rest of the packet is the pathname.
+    // SCM_RIGHTS for response socket attached.
+  };
+
+  struct Response {
+    int mError; // errno, or 0 for no error
+    // Followed by struct stat for stat/lstat.
+    // SCM_RIGHTS attached for successful open.
+  };
+
+  // This doesn't need to be the system's maximum path length, just
+  // the largest path that would be allowed by any policy.  (It's used
+  // to size a stack-allocated buffer.)
+  static const size_t kMaxPathLen = 4096;
+
+  static ssize_t RecvWithFd(int aFd, const iovec* aIO, size_t aNumIO,
+                            int* aPassedFdPtr);
+  static ssize_t SendWithFd(int aFd, const iovec* aIO, size_t aNumIO,
+                            int aPassedFd);
+};
+
+} // namespace mozilla
+
+#endif // mozilla_SandboxBrokerTypes_h
diff --git a/security/sandbox/linux/broker/moz.build b/security/sandbox/linux/broker/moz.build
new file mode 100644
index 00000000000..620d0011dfa
--- /dev/null
+++ b/security/sandbox/linux/broker/moz.build
@@ -0,0 +1,32 @@
+# -*- Mode: python; python-indent: 4; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+EXPORTS.mozilla += [
+    'SandboxBroker.h',
+    'SandboxBrokerCommon.h',
+]
+
+SOURCES += [
+    'SandboxBroker.cpp',
+    'SandboxBrokerCommon.cpp',
+]
+
+LOCAL_INCLUDES += [
+    '/security/sandbox/linux', # SandboxLogging.h
+    '/security/sandbox/linux/common', # SandboxInfo.h
+]
+
+# Need this for mozilla::ipc::FileDescriptor etc.
+include('/ipc/chromium/chromium-config.mozbuild')
+
+# Need this for safe_sprintf.h used by SandboxLogging.h,
+# but it has to be after ipc/chromium/src.
+LOCAL_INCLUDES += [
+    '/security/sandbox/chromium',
+]
+
+
+FINAL_LIBRARY = 'xul'
diff --git a/security/sandbox/linux/gtest/TestBroker.cpp b/security/sandbox/linux/gtest/TestBroker.cpp
new file mode 100644
index 00000000000..0fbe8fb4d1d
--- /dev/null
+++ b/security/sandbox/linux/gtest/TestBroker.cpp
@@ -0,0 +1,440 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gtest/gtest.h"
+
+#include "broker/SandboxBroker.h"
+#include "SandboxBrokerClient.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <sched.h>
+#include <semaphore.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "mozilla/Atomics.h"
+#include "mozilla/NullPtr.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/ipc/FileDescriptor.h"
+
+namespace mozilla {
+
+static const int MAY_ACCESS = SandboxBroker::MAY_ACCESS;
+static const int MAY_READ = SandboxBroker::MAY_READ;
+static const int MAY_WRITE = SandboxBroker::MAY_WRITE;
+//static const int MAY_CREATE = SandboxBroker::MAY_CREATE;
+static const auto AddAlways = SandboxBroker::Policy::AddAlways;
+
+class SandboxBrokerTest : public ::testing::Test
+{
+  UniquePtr<SandboxBroker> mServer;
+  UniquePtr<SandboxBrokerClient> mClient;
+
+  UniquePtr<const SandboxBroker::Policy> GetPolicy() const;
+
+  template<class C, void (C::* Main)()>
+  static void* ThreadMain(void* arg) {
+    (static_cast<C*>(arg)->*Main)();
+    return nullptr;
+  }
+
+protected:
+  int Open(const char* aPath, int aFlags) {
+    return mClient->Open(aPath, aFlags);
+  }
+  int Access(const char* aPath, int aMode) {
+    return mClient->Access(aPath, aMode);
+  }
+  int Stat(const char* aPath, struct stat* aStat) {
+    return mClient->Stat(aPath, aStat);
+  }
+  int LStat(const char* aPath, struct stat* aStat) {
+    return mClient->LStat(aPath, aStat);
+  }
+
+  virtual void SetUp() {
+    ipc::FileDescriptor fd;
+
+    mServer = SandboxBroker::Create(GetPolicy(), getpid(), fd);
+    ASSERT_NE(mServer, nullptr);
+    ASSERT_TRUE(fd.IsValid());
+    mClient.reset(new SandboxBrokerClient(dup(fd.PlatformHandle())));
+  }
+
+  template<class C, void (C::* Main)()>
+  void StartThread(pthread_t *aThread) {
+    ASSERT_EQ(0, pthread_create(aThread, nullptr, ThreadMain<C, Main>,
+                                static_cast<C*>(this)));
+  }
+
+  template<class C, void (C::* Main)()>
+  void RunOnManyThreads() {
+    static const int kNumThreads = 5;
+    pthread_t threads[kNumThreads];
+    for (int i = 0; i < kNumThreads; ++i) {
+      StartThread<C, Main>(&threads[i]);
+    }
+    for (int i = 0; i < kNumThreads; ++i) {
+      void* retval;
+      ASSERT_EQ(pthread_join(threads[i], &retval), 0);
+      ASSERT_EQ(retval, static_cast<void*>(nullptr));
+    }
+  }
+
+public:
+  void MultiThreadOpenWorker();
+  void MultiThreadStatWorker();
+};
+
+UniquePtr<const SandboxBroker::Policy>
+SandboxBrokerTest::GetPolicy() const
+{
+  UniquePtr<SandboxBroker::Policy> policy(new SandboxBroker::Policy());
+
+  policy->AddPath(MAY_READ | MAY_WRITE, "/dev/null", AddAlways);
+  policy->AddPath(MAY_READ, "/dev/zero", AddAlways);
+  policy->AddPath(MAY_READ, "/var/empty/qwertyuiop", AddAlways);
+  policy->AddPath(MAY_ACCESS, "/proc/self", AddAlways); // Warning: Linux-specific.
+
+  return Move(policy);
+}
+
+TEST_F(SandboxBrokerTest, OpenForRead)
+{
+  int fd;
+
+  fd = Open("/dev/null", O_RDONLY);
+  ASSERT_GE(fd, 0) << "Opening /dev/null failed.";
+  close(fd);
+  fd = Open("/dev/zero", O_RDONLY);
+  ASSERT_GE(fd, 0) << "Opening /dev/zero failed.";
+  close(fd);
+  fd = Open("/var/empty/qwertyuiop", O_RDONLY);
+  EXPECT_EQ(-ENOENT, fd) << "Opening allowed but nonexistent file succeeded.";
+  fd = Open("/proc/self", O_RDONLY);
+  EXPECT_EQ(-EACCES, fd) << "Opening stat-only file for read succeeded.";
+  fd = Open("/proc/self/stat", O_RDONLY);
+  EXPECT_EQ(-EACCES, fd) << "Opening disallowed file succeeded.";
+}
+
+TEST_F(SandboxBrokerTest, OpenForWrite)
+{
+  int fd;
+
+  fd = Open("/dev/null", O_WRONLY);
+  ASSERT_GE(fd, 0) << "Opening /dev/null write-only failed.";
+  close(fd);
+  fd = Open("/dev/null", O_RDWR);
+  ASSERT_GE(fd, 0) << "Opening /dev/null read/write failed.";
+  close(fd);
+  fd = Open("/dev/zero", O_WRONLY);
+  ASSERT_EQ(-EACCES, fd) << "Opening read-only-by-policy file write-only succeeded.";
+  fd = Open("/dev/zero", O_RDWR);
+  ASSERT_EQ(-EACCES, fd) << "Opening read-only-by-policy file read/write succeeded.";
+}
+
+TEST_F(SandboxBrokerTest, SimpleRead)
+{
+  int fd;
+  char c;
+
+  fd = Open("/dev/null", O_RDONLY);
+  ASSERT_GE(fd, 0);
+  EXPECT_EQ(0, read(fd, &c, 1));
+  close(fd);
+  fd = Open("/dev/zero", O_RDONLY);
+  ASSERT_GE(fd, 0);
+  ASSERT_EQ(1, read(fd, &c, 1));
+  EXPECT_EQ(c, '\0');
+}
+
+TEST_F(SandboxBrokerTest, Access)
+{
+  EXPECT_EQ(0, Access("/dev/null", F_OK));
+  EXPECT_EQ(0, Access("/dev/null", R_OK));
+  EXPECT_EQ(0, Access("/dev/null", W_OK));
+  EXPECT_EQ(0, Access("/dev/null", R_OK|W_OK));
+  EXPECT_EQ(-EACCES, Access("/dev/null", X_OK));
+  EXPECT_EQ(-EACCES, Access("/dev/null", R_OK|X_OK));
+
+  EXPECT_EQ(0, Access("/dev/zero", R_OK));
+  EXPECT_EQ(-EACCES, Access("/dev/zero", W_OK));
+  EXPECT_EQ(-EACCES, Access("/dev/zero", R_OK|W_OK));
+
+  EXPECT_EQ(-ENOENT, Access("/var/empty/qwertyuiop", R_OK));
+  EXPECT_EQ(-EACCES, Access("/var/empty/qwertyuiop", W_OK));
+
+  EXPECT_EQ(0, Access("/proc/self", F_OK));
+  EXPECT_EQ(-EACCES, Access("/proc/self", R_OK));
+
+  EXPECT_EQ(-EACCES, Access("/proc/self/stat", F_OK));
+}
+
+TEST_F(SandboxBrokerTest, Stat)
+{
+  struct stat brokeredStat, realStat;
+  ASSERT_EQ(0, stat("/dev/null", &realStat)) << "Shouldn't ever fail!";
+  EXPECT_EQ(0, Stat("/dev/null", &brokeredStat));
+  EXPECT_EQ(realStat.st_ino, brokeredStat.st_ino);
+  EXPECT_EQ(realStat.st_rdev, brokeredStat.st_rdev);
+
+  EXPECT_EQ(-ENOENT, Stat("/var/empty/qwertyuiop", &brokeredStat));
+  EXPECT_EQ(-EACCES, Stat("/dev", &brokeredStat));
+
+  EXPECT_EQ(0, Stat("/proc/self", &brokeredStat));
+  EXPECT_TRUE(S_ISDIR(brokeredStat.st_mode));
+}
+
+TEST_F(SandboxBrokerTest, LStat)
+{
+  struct stat brokeredStat, realStat;
+  ASSERT_EQ(0, lstat("/dev/null", &realStat));
+  EXPECT_EQ(0, LStat("/dev/null", &brokeredStat));
+  EXPECT_EQ(realStat.st_ino, brokeredStat.st_ino);
+  EXPECT_EQ(realStat.st_rdev, brokeredStat.st_rdev);
+
+  EXPECT_EQ(-ENOENT, LStat("/var/empty/qwertyuiop", &brokeredStat));
+  EXPECT_EQ(-EACCES, LStat("/dev", &brokeredStat));
+
+  EXPECT_EQ(0, LStat("/proc/self", &brokeredStat));
+  EXPECT_TRUE(S_ISLNK(brokeredStat.st_mode));
+}
+
+TEST_F(SandboxBrokerTest, MultiThreadOpen) {
+  RunOnManyThreads<SandboxBrokerTest,
+                   &SandboxBrokerTest::MultiThreadOpenWorker>();
+}
+void SandboxBrokerTest::MultiThreadOpenWorker() {
+  static const int kNumLoops = 10000;
+
+  for (int i = 1; i <= kNumLoops; ++i) {
+    int nullfd = Open("/dev/null", O_RDONLY);
+    int zerofd = Open("/dev/zero", O_RDONLY);
+    ASSERT_GE(nullfd, 0) << "Loop " << i << "/" << kNumLoops;
+    ASSERT_GE(zerofd, 0) << "Loop " << i << "/" << kNumLoops;
+    char c;
+    ASSERT_EQ(0, read(nullfd, &c, 1)) << "Loop " << i << "/" << kNumLoops;
+    ASSERT_EQ(1, read(zerofd, &c, 1)) << "Loop " << i << "/" << kNumLoops;
+    ASSERT_EQ('\0', c) << "Loop " << i << "/" << kNumLoops;
+    close(nullfd);
+    close(zerofd);
+  }
+}
+
+TEST_F(SandboxBrokerTest, MultiThreadStat) {
+  RunOnManyThreads<SandboxBrokerTest,
+                   &SandboxBrokerTest::MultiThreadStatWorker>();
+}
+void SandboxBrokerTest::MultiThreadStatWorker() {
+  static const int kNumLoops = 7500;
+  struct stat nullStat, zeroStat, selfStat;
+  dev_t realNullDev, realZeroDev;
+  ino_t realSelfInode;
+
+  ASSERT_EQ(0, stat("/dev/null", &nullStat)) << "Shouldn't ever fail!";
+  ASSERT_EQ(0, stat("/dev/zero", &zeroStat)) << "Shouldn't ever fail!";
+  ASSERT_EQ(0, lstat("/proc/self", &selfStat)) << "Shouldn't ever fail!";
+  ASSERT_TRUE(S_ISLNK(selfStat.st_mode)) << "Shouldn't ever fail!";
+  realNullDev = nullStat.st_rdev;
+  realZeroDev = zeroStat.st_rdev;
+  realSelfInode = selfStat.st_ino;
+  for (int i = 1; i <= kNumLoops; ++i) {
+    ASSERT_EQ(0, Stat("/dev/null", &nullStat))
+      << "Loop " << i << "/" << kNumLoops;
+    ASSERT_EQ(0, Stat("/dev/zero", &zeroStat))
+      << "Loop " << i << "/" << kNumLoops;
+    ASSERT_EQ(0, LStat("/proc/self", &selfStat))
+      << "Loop " << i << "/" << kNumLoops;
+
+    ASSERT_EQ(realNullDev, nullStat.st_rdev)
+      << "Loop " << i << "/" << kNumLoops;
+    ASSERT_EQ(realZeroDev, zeroStat.st_rdev)
+      << "Loop " << i << "/" << kNumLoops;
+    ASSERT_TRUE(S_ISLNK(selfStat.st_mode))
+      << "Loop " << i << "/" << kNumLoops;
+    ASSERT_EQ(realSelfInode, selfStat.st_ino)
+      << "Loop " << i << "/" << kNumLoops;
+  }
+}
+
+#if 0
+class SandboxBrokerSigStress : public SandboxBrokerTest
+{
+  int mSigNum;
+  struct sigaction mOldAction;
+  Atomic<void*> mVoidPtr;
+
+  static void SigHandler(int aSigNum, siginfo_t* aSigInfo, void *aCtx) {
+    ASSERT_EQ(SI_QUEUE, aSigInfo->si_code);
+    SandboxBrokerSigStress* that =
+      static_cast<SandboxBrokerSigStress*>(aSigInfo->si_value.sival_ptr);
+    ASSERT_EQ(that->mSigNum, aSigNum);
+    that->DoSomething();
+  }
+
+protected:
+  Atomic<int> mTestIter;
+  sem_t mSemaphore;
+
+  void SignalThread(pthread_t aThread) {
+    union sigval sv;
+    sv.sival_ptr = this;
+    ASSERT_NE(0, mSigNum);
+    ASSERT_EQ(0, pthread_sigqueue(aThread, mSigNum, sv));
+  }
+
+  virtual void SetUp() {
+    ASSERT_EQ(0, sem_init(&mSemaphore, 0, 0));
+    mVoidPtr = nullptr;
+    mSigNum = 0;
+    for (int sigNum = SIGRTMIN; sigNum < SIGRTMAX; ++sigNum) {
+      ASSERT_EQ(0, sigaction(sigNum, nullptr, &mOldAction));
+      if ((mOldAction.sa_flags & SA_SIGINFO) == 0 &&
+          mOldAction.sa_handler == SIG_DFL) {
+        struct sigaction newAction;
+        PodZero(&newAction);
+        newAction.sa_flags = SA_SIGINFO;
+        newAction.sa_sigaction = SigHandler;
+        ASSERT_EQ(0, sigaction(sigNum, &newAction, nullptr));
+        mSigNum = sigNum;
+        break;
+      }
+    }
+    ASSERT_NE(mSigNum, 0);
+
+    SandboxBrokerTest::SetUp();
+  }
+
+  virtual void TearDown() {
+    ASSERT_EQ(0, sem_destroy(&mSemaphore));
+    if (mSigNum != 0) {
+      ASSERT_EQ(0, sigaction(mSigNum, &mOldAction, nullptr));
+    }
+    if (mVoidPtr) {
+      free(mVoidPtr);
+    }
+  }
+
+  void DoSomething();
+
+public:
+  void MallocWorker();
+  void FreeWorker();
+};
+
+TEST_F(SandboxBrokerSigStress, StressTest)
+{
+  static const int kIters = 6250;
+  static const int kNsecPerIterPerIter = 4;
+  struct timespec delay = { 0, 0 };
+  pthread_t threads[2];
+
+  mTestIter = kIters;
+
+  StartThread<SandboxBrokerSigStress,
+              &SandboxBrokerSigStress::MallocWorker>(&threads[0]);
+  StartThread<SandboxBrokerSigStress,
+              &SandboxBrokerSigStress::FreeWorker>(&threads[1]);
+
+  for (int i = kIters; i > 0; --i) {
+    SignalThread(threads[i % 2]);
+    while (sem_wait(&mSemaphore) == -1 && errno == EINTR)
+      /* retry */;
+    ASSERT_EQ(i - 1, mTestIter);
+    delay.tv_nsec += kNsecPerIterPerIter;
+    struct timespec req = delay, rem;
+    while (nanosleep(&req, &rem) == -1 && errno == EINTR) {
+      req = rem;
+    }
+  }
+  void *retval;
+  ASSERT_EQ(0, pthread_join(threads[0], &retval));
+  ASSERT_EQ(nullptr, retval);
+  ASSERT_EQ(0, pthread_join(threads[1], &retval));
+  ASSERT_EQ(nullptr, retval);
+}
+
+void
+SandboxBrokerSigStress::MallocWorker()
+{
+  static const size_t kSize = 64;
+
+  void* mem = malloc(kSize);
+  while (mTestIter > 0) {
+    ASSERT_NE(mem, mVoidPtr);
+    mem = mVoidPtr.exchange(mem);
+    if (mem) {
+      sched_yield();
+    } else {
+      mem = malloc(kSize);
+    }
+  }
+  if (mem) {
+    free(mem);
+  }
+}
+
+void
+SandboxBrokerSigStress::FreeWorker()
+{
+  void *mem = nullptr;
+  while (mTestIter > 0) {
+    mem = mVoidPtr.exchange(mem);
+    if (mem) {
+      free(mem);
+      mem = nullptr;
+    } else {
+      sched_yield();
+    }
+  }
+}
+
+void
+SandboxBrokerSigStress::DoSomething()
+{
+  int fd;
+  char c;
+  struct stat st;
+
+  //fprintf(stderr, "Don't try this at home: %d\n", static_cast<int>(mTestIter));
+  switch (mTestIter % 5) {
+  case 0:
+    fd = Open("/dev/null", O_RDWR);
+    ASSERT_GE(fd, 0);
+    ASSERT_EQ(0, read(fd, &c, 1));
+    close(fd);
+    break;
+  case 1:
+    fd = Open("/dev/zero", O_RDONLY);
+    ASSERT_GE(fd, 0);
+    ASSERT_EQ(1, read(fd, &c, 1));
+    ASSERT_EQ('\0', c);
+    close(fd);
+    break;
+  case 2:
+    ASSERT_EQ(0, Access("/dev/null", W_OK));
+    break;
+  case 3:
+    ASSERT_EQ(0, Stat("/proc/self", &st));
+    ASSERT_TRUE(S_ISDIR(st.st_mode));
+    break;
+  case 4:
+    ASSERT_EQ(0, LStat("/proc/self", &st));
+    ASSERT_TRUE(S_ISLNK(st.st_mode));
+    break;
+  }
+  mTestIter--;
+  sem_post(&mSemaphore);
+}
+#endif
+
+} // namespace mozilla
diff --git a/security/sandbox/linux/gtest/TestBrokerPolicy.cpp b/security/sandbox/linux/gtest/TestBrokerPolicy.cpp
new file mode 100644
index 00000000000..4eb66f1888a
--- /dev/null
+++ b/security/sandbox/linux/gtest/TestBrokerPolicy.cpp
@@ -0,0 +1,60 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gtest/gtest.h"
+
+#include "broker/SandboxBroker.h"
+
+namespace mozilla {
+
+static const int MAY_ACCESS = SandboxBroker::MAY_ACCESS;
+static const int MAY_READ = SandboxBroker::MAY_READ;
+static const int MAY_WRITE = SandboxBroker::MAY_WRITE;
+//static const int MAY_CREATE = SandboxBroker::MAY_CREATE;
+static const auto AddAlways = SandboxBroker::Policy::AddAlways;
+
+TEST(SandboxBrokerPolicyLookup, Simple)
+{
+  SandboxBroker::Policy p;
+  p.AddPath(MAY_READ, "/dev/urandom", AddAlways);
+
+  EXPECT_NE(0, p.Lookup("/dev/urandom")) << "Added path not found.";
+  EXPECT_EQ(MAY_ACCESS | MAY_READ, p.Lookup("/dev/urandom"))
+    << "Added path found with wrong perms.";
+  EXPECT_EQ(0, p.Lookup("/etc/passwd")) << "Non-added path was found.";
+}
+
+TEST(SandboxBrokerPolicyLookup, CopyCtor)
+{
+  SandboxBroker::Policy psrc;
+  psrc.AddPath(MAY_READ | MAY_WRITE, "/dev/null", AddAlways);
+  SandboxBroker::Policy pdst(psrc);
+  psrc.AddPath(MAY_READ, "/dev/zero", AddAlways);
+  pdst.AddPath(MAY_READ, "/dev/urandom", AddAlways);
+
+  EXPECT_EQ(MAY_ACCESS | MAY_READ | MAY_WRITE, psrc.Lookup("/dev/null"))
+    << "Common path absent in copy source.";
+  EXPECT_EQ(MAY_ACCESS | MAY_READ | MAY_WRITE, pdst.Lookup("/dev/null"))
+    << "Common path absent in copy destination.";
+
+  EXPECT_EQ(MAY_ACCESS | MAY_READ, psrc.Lookup("/dev/zero"))
+    << "Source-only path is absent.";
+  EXPECT_EQ(0, pdst.Lookup("/dev/zero"))
+    << "Source-only path is present in copy destination.";
+
+  EXPECT_EQ(0, psrc.Lookup("/dev/urandom"))
+    << "Destination-only path is present in copy source.";
+  EXPECT_EQ(MAY_ACCESS | MAY_READ, pdst.Lookup("/dev/urandom"))
+    << "Destination-only path is absent.";
+
+  EXPECT_EQ(0, psrc.Lookup("/etc/passwd"))
+    << "Non-added path is present in copy source.";
+  EXPECT_EQ(0, pdst.Lookup("/etc/passwd"))
+    << "Non-added path is present in copy source.";
+}
+
+} // namespace mozilla
+
diff --git a/security/sandbox/linux/gtest/moz.build b/security/sandbox/linux/gtest/moz.build
index 9c2eab28c85..a0ac3ff5946 100644
--- a/security/sandbox/linux/gtest/moz.build
+++ b/security/sandbox/linux/gtest/moz.build
@@ -7,7 +7,10 @@
 Library('sandboxtest')
 
 SOURCES = [
+    '../SandboxBrokerClient.cpp',
     '../SandboxUtil.cpp',
+    'TestBroker.cpp',
+    'TestBrokerPolicy.cpp',
     'TestSandboxUtil.cpp',
 ]
 
@@ -15,6 +18,9 @@ LOCAL_INCLUDES += [
     '/security/sandbox/linux',
     '/security/sandbox/linux/common',
 ]
+
+include('/ipc/chromium/chromium-config.mozbuild')
+
 LOCAL_INCLUDES += [
     '/security/sandbox/chromium',
 ]
diff --git a/security/sandbox/linux/moz.build b/security/sandbox/linux/moz.build
index d8acd030682..712269b4b6c 100644
--- a/security/sandbox/linux/moz.build
+++ b/security/sandbox/linux/moz.build
@@ -55,8 +55,10 @@ SOURCES += [
     '../chromium/sandbox/linux/seccomp-bpf/syscall.cc',
     '../chromium/sandbox/linux/seccomp-bpf/syscall_iterator.cc',
     '../chromium/sandbox/linux/seccomp-bpf/trap.cc',
+    'broker/SandboxBrokerCommon.cpp',
     'LinuxCapabilities.cpp',
     'Sandbox.cpp',
+    'SandboxBrokerClient.cpp',
     'SandboxChroot.cpp',
     'SandboxFilter.cpp',
     'SandboxFilterUtil.cpp',
@@ -90,7 +92,12 @@ if CONFIG['OS_TARGET'] != 'Android':
         'rt',
     ]
 
+USE_LIBS += [
+    'mfbt',
+]
+
 DIRS += [
+    'broker',
     'common',
     'glue',
 ]