1 files changed, 272 insertions, 0 deletions
diff --git a/security/sandbox/linux/SandboxInfo.cpp b/security/sandbox/linux/SandboxInfo.cpp
new file mode 100644
index 000000000..f813fb026
--- /dev/null
+++ b/security/sandbox/linux/SandboxInfo.cpp
@@ -0,0 +1,272 @@
+/* -*- 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 "SandboxInfo.h"
+#include "SandboxLogging.h"
+#include "LinuxSched.h"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "base/posix/eintr_wrapper.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/ArrayUtils.h"
+#include "sandbox/linux/system_headers/linux_seccomp.h"
+#include "sandbox/linux/system_headers/linux_syscalls.h"
+
+#ifdef MOZ_VALGRIND
+#include <valgrind/valgrind.h>
+#endif
+
+
+// A note about assertions: in general, the worst thing this module
+// should be able to do is disable sandboxing features, so release
+// asserts or MOZ_CRASH should be avoided, even for seeming
+// impossibilities like an unimplemented syscall returning success
+// (which has happened: https://crbug.com/439795 ).
+//
+// MOZ_DIAGNOSTIC_ASSERT (debug builds, plus Nightly/Aurora non-debug)
+// is probably the best choice for conditions that shouldn't be able
+// to fail without the help of bugs in the kernel or system libraries.
+//
+// Regardless of assertion type, whatever condition caused it to fail
+// should generally also disable the corresponding feature on builds
+// that omit the assertion.
+
+namespace mozilla {
+
+// Bug 1229136: this is copied from ../SandboxUtil.cpp to avoid
+// complicated build issues; renamespaced to avoid the possibility of
+// symbol conflict.
+namespace {
+
+static bool
+IsSingleThreaded()
+{
+  // This detects the thread count indirectly.  /proc/<pid>/task has a
+  // subdirectory for each thread in <pid>'s thread group, and the
+  // link count on the "task" directory follows Unix expectations: the
+  // link from its parent, the "." link from itself, and the ".." link
+  // from each subdirectory; thus, 2+N links for N threads.
+  struct stat sb;
+  if (stat("/proc/self/task", &sb) < 0) {
+    MOZ_DIAGNOSTIC_ASSERT(false, "Couldn't access /proc/self/task!");
+    return false;
+  }
+  MOZ_DIAGNOSTIC_ASSERT(sb.st_nlink >= 3);
+  return sb.st_nlink == 3;
+}
+
+} // anonymous namespace
+
+static bool
+HasSeccompBPF()
+{
+  // Allow simulating the absence of seccomp-bpf support, for testing.
+  if (getenv("MOZ_FAKE_NO_SANDBOX")) {
+    return false;
+  }
+
+  // Valgrind and the sandbox don't interact well, probably because Valgrind
+  // does various system calls which aren't allowed, even if Firefox itself
+  // is playing by the rules.
+# if defined(MOZ_VALGRIND)
+  if (RUNNING_ON_VALGRIND) {
+    return false;
+  }
+# endif
+
+  // Determine whether seccomp-bpf is supported by trying to
+  // enable it with an invalid pointer for the filter.  This will
+  // fail with EFAULT if supported and EINVAL if not, without
+  // changing the process's state.
+
+  int rv = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, nullptr);
+  MOZ_DIAGNOSTIC_ASSERT(rv == -1, "prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER,"
+                        " nullptr) didn't fail");
+  MOZ_DIAGNOSTIC_ASSERT(errno == EFAULT || errno == EINVAL);
+  return rv == -1 && errno == EFAULT;
+}
+
+static bool
+HasSeccompTSync()
+{
+  // Similar to above, but for thread-sync mode.  See also Chromium's
+  // sandbox::SandboxBPF::SupportsSeccompThreadFilterSynchronization
+  if (getenv("MOZ_FAKE_NO_SECCOMP_TSYNC")) {
+    return false;
+  }
+  int rv = syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER,
+                   SECCOMP_FILTER_FLAG_TSYNC, nullptr);
+  MOZ_DIAGNOSTIC_ASSERT(rv == -1, "seccomp(..., SECCOMP_FILTER_FLAG_TSYNC,"
+                        " nullptr) didn't fail");
+  MOZ_DIAGNOSTIC_ASSERT(errno == EFAULT || errno == EINVAL || errno == ENOSYS);
+  return rv == -1 && errno == EFAULT;
+}
+
+static bool
+HasUserNamespaceSupport()
+{
+  // Note: the /proc/<pid>/ns/* files track setns(2) support, which in
+  // some cases (e.g., pid) significantly postdates kernel support for
+  // the namespace type, so in general this type of check could be a
+  // false negative.  However, for user namespaces, any kernel new
+  // enough for the feature to be usable for us has setns support
+  // (v3.8), so this is okay.
+  //
+  // The non-user namespaces all default to "y" in init/Kconfig, but
+  // check them explicitly in case someone has a weird custom config.
+  static const char* const paths[] = {
+    "/proc/self/ns/user",
+    "/proc/self/ns/pid",
+    "/proc/self/ns/net",
+    "/proc/self/ns/ipc",
+  };
+  for (size_t i = 0; i < ArrayLength(paths); ++i) {
+    if (access(paths[i], F_OK) == -1) {
+      MOZ_ASSERT(errno == ENOENT);
+      return false;
+    }
+  }
+  return true;
+}
+
+static bool
+CanCreateUserNamespace()
+{
+  // Unfortunately, the only way to verify that this process can
+  // create a new user namespace is to actually create one; because
+  // this process's namespaces shouldn't be side-effected (yet), it's
+  // necessary to clone (and collect) a child process.  See also
+  // Chromium's sandbox::Credentials::SupportsNewUserNS.
+  //
+  // This is somewhat more expensive than the other tests, so it's
+  // cached in the environment to prevent child processes from having
+  // to re-run the test.
+  //
+  // This is run at static initializer time, while single-threaded, so
+  // locking isn't needed to access the environment.
+  static const char kCacheEnvName[] = "MOZ_ASSUME_USER_NS";
+  const char* cached = getenv(kCacheEnvName);
+  if (cached) {
+    return cached[0] > '0';
+  }
+
+  // Valgrind might allow the clone, but doesn't know what to do with
+  // unshare.  Check for that by unsharing nothing.  (Valgrind will
+  // probably need sandboxing disabled entirely, but no need to break
+  // things worse than strictly necessary.)
+  if (syscall(__NR_unshare, 0) != 0) {
+#ifdef MOZ_VALGRIND
+    MOZ_ASSERT(errno == ENOSYS);
+#else
+    // If something else can cause that call to fail, we's like to know
+    // about it; the right way to handle it might not be the same.
+    MOZ_ASSERT(false);
+#endif
+    return false;
+  }
+
+  pid_t pid = syscall(__NR_clone, SIGCHLD | CLONE_NEWUSER,
+                      nullptr, nullptr, nullptr, nullptr);
+  if (pid == 0) {
+    // In the child.  Do as little as possible.
+    _exit(0);
+  }
+  if (pid == -1) {
+    // Failure.
+    MOZ_ASSERT(errno == EINVAL || // unsupported
+               errno == EPERM  || // root-only, or we're already chrooted
+               errno == EUSERS);  // already at user namespace nesting limit
+    setenv(kCacheEnvName, "0", 1);
+    return false;
+  }
+  // Otherwise, in the parent and successful.
+  bool waitpid_ok = HANDLE_EINTR(waitpid(pid, nullptr, 0)) == pid;
+  MOZ_ASSERT(waitpid_ok);
+  if (!waitpid_ok) {
+    return false;
+  }
+  setenv(kCacheEnvName, "1", 1);
+  return true;
+}
+
+/* static */
+SandboxInfo SandboxInfo::sSingleton = SandboxInfo();
+
+SandboxInfo::SandboxInfo() {
+  int flags = 0;
+  static_assert(sizeof(flags) >= sizeof(Flags), "enum Flags fits in an int");
+
+  if (HasSeccompBPF()) {
+    flags |= kHasSeccompBPF;
+    if (HasSeccompTSync()) {
+      flags |= kHasSeccompTSync;
+    }
+  }
+
+  // Detect the threading-problem signal from the parent process.
+  if (getenv("MOZ_SANDBOX_UNEXPECTED_THREADS")) {
+    flags |= kUnexpectedThreads;
+  } else {
+    if (HasUserNamespaceSupport()) {
+      flags |= kHasPrivilegedUserNamespaces;
+      if (CanCreateUserNamespace()) {
+        flags |= kHasUserNamespaces;
+      }
+    }
+  }
+
+#ifdef MOZ_CONTENT_SANDBOX
+  if (!getenv("MOZ_DISABLE_CONTENT_SANDBOX")) {
+    flags |= kEnabledForContent;
+  }
+  if (getenv("MOZ_PERMISSIVE_CONTENT_SANDBOX")) {
+    flags |= kPermissive;
+  }
+#endif
+#ifdef MOZ_GMP_SANDBOX
+  if (!getenv("MOZ_DISABLE_GMP_SANDBOX")) {
+    flags |= kEnabledForMedia;
+  }
+#endif
+  if (getenv("MOZ_SANDBOX_VERBOSE")) {
+    flags |= kVerbose;
+  }
+
+  mFlags = static_cast<Flags>(flags);
+}
+
+/* static */ void
+SandboxInfo::ThreadingCheck()
+{
+  // Allow MOZ_SANDBOX_UNEXPECTED_THREADS to be set manually for testing.
+  if (IsSingleThreaded() &&
+      !getenv("MOZ_SANDBOX_UNEXPECTED_THREADS")) {
+    return;
+  }
+  SANDBOX_LOG_ERROR("unexpected multithreading found; this prevents using"
+                    " namespace sandboxing.%s",
+                    // getenv isn't thread-safe, but see below.
+                    getenv("LD_PRELOAD") ? "  (If you're LD_PRELOAD'ing"
+                    " nVidia GL: that's not necessary for Gecko.)" : "");
+
+  // Propagate this information for use by child processes.  (setenv
+  // isn't thread-safe, but other threads are from non-Gecko code so
+  // they wouldn't be using NSPR; we have to hope for the best.)
+  setenv("MOZ_SANDBOX_UNEXPECTED_THREADS", "1", 0);
+  int flags = sSingleton.mFlags;
+  flags |= kUnexpectedThreads;
+  flags &= ~(kHasUserNamespaces | kHasPrivilegedUserNamespaces);
+  sSingleton.mFlags = static_cast<Flags>(flags);
+}
+
+} // namespace mozilla