Linux Sandbox: Add support for SECCOMP_RET_TRACE.

sandbox/linux/seccomp-bpf/verifier.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 <string.h>
 
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf_policy.h"
 #include "sandbox/linux/seccomp-bpf/syscall_iterator.h"
 #include "sandbox/linux/seccomp-bpf/verifier.h"
@@ skipping 403 matching lines @@
         Ld(&state, insn, err);
         break;
       case BPF_JMP:
         Jmp(&state, insn, err);
         break;
       case BPF_RET: {
         uint32_t r = Ret(&state, insn, err);
         switch (r & SECCOMP_RET_ACTION) {
           case SECCOMP_RET_TRAP:
           case SECCOMP_RET_ERRNO:
+          case SECCOMP_RET_TRACE:
           case SECCOMP_RET_ALLOW:
             break;
           case SECCOMP_RET_KILL:     // We don't ever generate this
-          case SECCOMP_RET_TRACE:    // We don't ever generate this
           case SECCOMP_RET_INVALID:  // Should never show up in BPF program
           default:
             *err = "Unexpected return code found in BPF program";
             return 0;
         }
         return r;
       }
       case BPF_ALU:
         Alu(&state, insn, err);
         break;
       default:
         *err = "Unexpected instruction in BPF program";
         break;
     }
   }
   return 0;
 }
 
 }  // namespace sandbox