Linux sandbox: fill all parameters when detecting seccomp syscall.

sandbox/linux/seccomp-bpf/sandbox_bpf.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
 
 // Some headers on Android are missing cdefs: crbug.com/172337.
 // (We can't use OS_ANDROID here since build_config.h is not included).
 #if defined(ANDROID)
 #include <sys/cdefs.h>
@@ skipping 474 matching lines @@
     }
   }
   return status_;
 }
 
 // static
 SandboxBPF::SandboxStatus
 SandboxBPF::SupportsSeccompThreadFilterSynchronization() {
   // Applying NO_NEW_PRIVS, a BPF filter, and synchronizing the filter across
   // the thread group are all handled atomically by this syscall.
-  int rv = syscall(__NR_seccomp);
+  const int rv = syscall(
+      __NR_seccomp, SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_TSYNC, NULL);
 
-  // The system call should have failed with EINVAL.
-  if (rv != -1) {
-    NOTREACHED();
-    return STATUS_UNKNOWN;
+  if (rv == -1 && errno == EFAULT) {
+    return STATUS_AVAILABLE;
+  } else {
+    // TODO(jln): turn these into DCHECK after 417888 is considered fixed.
+    CHECK_EQ(-1, rv);
+    CHECK(ENOSYS == errno || EINVAL == errno);
+    return STATUS_UNSUPPORTED;
   }
-
-  if (errno == EINVAL || errno == EFAULT)
-    return STATUS_AVAILABLE;
-
-  // errno is probably ENOSYS, indicating the system call is not available.
-  DCHECK_EQ(errno, ENOSYS);
-  return STATUS_UNSUPPORTED;
 }
 
 void SandboxBPF::set_proc_fd(int proc_fd) { proc_fd_ = proc_fd; }
 
 bool SandboxBPF::StartSandbox(SandboxThreadState thread_state) {
   CHECK(thread_state == PROCESS_SINGLE_THREADED ||
         thread_state == PROCESS_MULTI_THREADED);
 
   if (status_ == STATUS_UNSUPPORTED || status_ == STATUS_UNAVAILABLE) {
     SANDBOX_DIE(
@@ skipping 617 matching lines @@
   }
 }
 
 ErrorCode SandboxBPF::Kill(const char* msg) {
   return Trap(BPFFailure, const_cast<char*>(msg));
 }
 
 SandboxBPF::SandboxStatus SandboxBPF::status_ = STATUS_UNKNOWN;
 
 }  // namespace sandbox