Refactored ErrorCode into it's own class

sandbox/linux/seccomp-bpf/errorcode.h

+// 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.
+
+#ifndef SANDBOX_LINUX_SECCOMP_BPF_ERRORCODE_H__
+#define SANDBOX_LINUX_SECCOMP_BPF_ERRORCODE_H__
+
+namespace playground2 {
+
+struct arch_seccomp_data;
+
+// This class holds all the possible values that can returned by a sandbox
+// policy.
+// We can either wrap a symbolic ErrorCode (i.e. ERR_XXX enum values), an
+// errno value (in the range 1..4095), a pointer to a TrapFnc callback
+// handling a SECCOMP_RET_TRAP trap, or a complex constraint.
+// All of the commonly used values are stored in the "err_" field. So, code
+// that is using the ErrorCode class typically operates on a single 32bit
+// field.
+class ErrorCode {
+ public:
+  enum {
+    // Allow this system call.
+    ERR_ALLOWED   = 0x0000,
+
+    // Deny the system call with a particular "errno" value.
+    ERR_MIN_ERRNO = 1,
+    ERR_MAX_ERRNO = 4095,
+
+    // This code should never be used directly, it is used internally only.
+    ERR_INVALID   = -1,
+  };
+
+  // TrapFnc is a pointer to a function that handles Seccomp traps in
+  // user-space. The seccomp policy can request that a trap handler gets
+  // installed; it does so by returning a suitable ErrorCode() from the
+  // syscallEvaluator. See the ErrorCode() constructor for how to pass in
+  // the function pointer.
+  // Please note that TrapFnc is executed from signal context and must be
+  // async-signal safe:
+  // http://pubs.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html
+  typedef intptr_t (*TrapFnc)(const struct arch_seccomp_data& args, void *aux);
+
+  enum ArgType {
+    TP_32BIT, TP_64BIT,
+  };
+
+  enum Operation {
+    OP_EQUAL, OP_GREATER, OP_GREATER_EQUAL, OP_HAS_BITS,
+    OP_NUM_OPS,
+  };
+
+  // We allow the default constructor, as it makes the ErrorCode class
+  // much easier to use. But if we ever encounter an invalid ErrorCode
+  // when compiling a BPF filter, we deliberately generate an invalid
+  // program that will get flagged both by our Verifier class and by
+  // the Linux kernel.
+  ErrorCode() :
+      error_type_(ET_INVALID),
+      err_(SECCOMP_RET_INVALID) {
+  }
+  explicit ErrorCode(int err);
+
+  // For all practical purposes, ErrorCodes are treated as if they were
+  // structs. The copy constructor and assignment operator are trivial and
+  // we do not need to explicitly specify them.
+  // Most notably, it is in fact perfectly OK to directly copy the passed_ and
+  // failed_ field. They only ever get set by our private constructor, and the
+  // callers handle life-cycle management for these objects.
+
+  // Destructor
+  ~ErrorCode() { }
+
+  bool Equals(const ErrorCode& err) const;
+  bool LessThan(const ErrorCode& err) const;
+
+  uint32_t err() const { return err_; }
+
+  struct LessThan {
+    bool operator()(const ErrorCode& a, const ErrorCode& b) const {
+      return a.LessThan(b);
+    }
+  };
+
+ private:
+  friend class Sandbox;
+  friend class Verifier;
+
+  enum ErrorType {
+    ET_INVALID, ET_SIMPLE, ET_TRAP, ET_COND,
+  };
+
+  // If we are wrapping a callback, we must assign a unique id. This id is
+  // how the kernel tells us which one of our different SECCOMP_RET_TRAP
+  // cases has been triggered.
+  ErrorCode(TrapFnc fnc, const void *aux, uint16_t id);
+
+  // Some system calls require inspection of arguments. This constructor
+  // allows us to specify additional constraints.
+  ErrorCode(int argno, ArgType width, Operation op, uint64_t value,
+            const ErrorCode *passed, const ErrorCode *failed);
+
+  ErrorType error_type_;
+
+  union {
+    // Fields needed for SECCOMP_RET_TRAP callbacks
+    struct {
+      TrapFnc fnc_;              // Callback function and arg, if trap was
+      void    *aux_;             //   triggered by the kernel's BPF filter.
+    };
+
+    // Fields needed when inspecting additional arguments.
+    struct {
+      uint64_t  value_;          // Value that we are comparing with.
+      int       argno_;          // Syscall arg number that we are inspecting.
+      ArgType   width_;          // Whether we are looking at a 32/64bit value.
+      Operation op_;             // Comparison operation.
+      const ErrorCode *passed_;  // Value to be returned if comparison passed,
+      const ErrorCode *failed_;  //   or if it failed.
+    };
+  };
+
+  // 32bit field used for all possible types of ErrorCode values. This is
+  // the value that uniquely identifies any ErrorCode and it (typically) can
+  // be emitted directly into a BPF filter program.
+  uint32_t err_;
+
+};
+
+}  // namespace
+
+#endif  // SANDBOX_LINUX_SECCOMP_BPF_ERRORCODE_H__