Linux sandbox: Disallow get_robust_list and set_robust_list.

These are only used for futexes that are shared between processes, which should not be happening in Chromium.
BUG=413855

Review URL: https://codereview.chromium.org/569713004

Cr-Commit-Position: refs/heads/master@{#294986}

sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc

@@ -153,6 +153,9 @@ ResultExpr EvaluateSyscallImpl(int fs_denied_errno,
   if (sysno == __NR_futex)
     return RestrictFutex();
 
+  if (sysno == __NR_set_robust_list)
+    return Error(EPERM);
+
   if (sysno == __NR_getpriority || sysno ==__NR_setpriority)
     return RestrictGetSetpriority(current_pid);
 

sandbox/linux/seccomp-bpf-helpers/syscall_sets.cc

@@ -402,7 +402,6 @@ bool SyscallSets::IsAllowedFutex(int sysno) {
   switch (sysno) {
     case __NR_get_robust_list:
     case __NR_set_robust_list:
-      return true;
     case __NR_futex:
     default:
       return false;