Bug 1176099 - Add hooks for sigprocmask/pthread_sigmask. r=jld r=glandium

security/sandbox/linux/SandboxHooks.cpp

@@ -0,0 +1,66 @@
+/* -*- 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 <dlfcn.h>
+#include <signal.h>
+#include <errno.h>
+
+#include "mozilla/Types.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+// This file defines a hook for sigprocmask() and pthread_sigmask().
+// Bug 1176099: some threads block SIGSYS signal which breaks our seccomp-bpf
+// sandbox. To avoid this, we intercept the call and remove SIGSYS.
+//
+// ENOSYS indicates an error within the hook function itself.
+static int HandleSigset(int (*aRealFunc)(int, const sigset_t*, sigset_t*),
+                        int aHow, const sigset_t* aSet,
+                        sigset_t* aOldSet, bool aUseErrno)
+{
+  if (!aRealFunc) {
+    if (aUseErrno) {
+      errno = ENOSYS;
+      return -1;
+    }
+
+    return ENOSYS;
+  }
+
+  // Avoid unnecessary work
+  if (aHow == SIG_UNBLOCK || !sigismember(aSet, SIGSYS))
+    return aRealFunc(aHow, aSet, aOldSet);
+
+  sigset_t newSet = *aSet;
+  if (sigdelset(&newSet, SIGSYS) != 0) {
+    if (aUseErrno) {
+      errno = ENOSYS;
+      return -1;
+    }
+
+    return ENOSYS;
+  }
+
+  return aRealFunc(aHow, &newSet, aOldSet);
+}
+
+extern "C" MOZ_EXPORT int
+sigprocmask(int how, const sigset_t* set, sigset_t* oldset)
+{
+  static auto sRealFunc = (int (*)(int, const sigset_t*, sigset_t*))
+    dlsym(RTLD_NEXT, "sigprocmask");
+
+  return HandleSigset(sRealFunc, how, set, oldset, true);
+}
+
+extern "C" MOZ_EXPORT int
+pthread_sigmask(int how, const sigset_t* set, sigset_t* oldset)
+{
+  static auto sRealFunc = (int (*)(int, const sigset_t*, sigset_t*))
+    dlsym(RTLD_NEXT, "pthread_sigmask");
+
+  return HandleSigset(sRealFunc, how, set, oldset, false);
+}

security/sandbox/linux/moz.build

@@ -4,6 +4,12 @@
 # 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/.
 
+# WARNING: On desktop Linux, SandboxHooks.cpp must be statically compiled
+# into the main executable in order to function properly.
+# This is currently the case, but if mozsandbox is moved to its own
+# shared library, something needs to change regarding SandboxHooks.cpp.
+# See Bug 1176099 for further details.
+
 if CONFIG['OS_TARGET'] == 'Android':
     SharedLibrary('mozsandbox')
     USE_LIBS += [
@@ -62,6 +68,7 @@ SOURCES += [
     'SandboxChroot.cpp',
     'SandboxFilter.cpp',
     'SandboxFilterUtil.cpp',
+    'SandboxHooks.cpp',
     'SandboxLogging.cpp',
     'SandboxUtil.cpp',
 ]