base/file_descriptor_shuffle.cc

   1 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/file_descriptor_shuffle.h"
   6
   7 #include <errno.h>
   8 #include <unistd.h>
   9
  10 #include "base/eintr_wrapper.h"
  11 #include "base/logging.h"
  12
  13 namespace base {
  14
  15 bool PerformInjectiveMultimapDestructive(
  16     InjectiveMultimap* m, InjectionDelegate* delegate) {
  17   static const size_t kMaxExtraFDs = 16;
  18   int extra_fds[kMaxExtraFDs];
  19   unsigned next_extra_fd = 0;
  20
  21   // DANGER: this function may not allocate.
  22
  23   for (InjectiveMultimap::iterator i = m->begin(); i != m->end(); ++i) {
  24     int temp_fd = -1;
  25
  26     // We DCHECK the injectiveness of the mapping.
  27     for (InjectiveMultimap::iterator j = i + 1; j != m->end(); ++j) {
  28       DCHECK(i->dest != j->dest) << "Both fd " << i->source
  29           << " and " << j->source << " map to " << i->dest;
  30     }
  31
  32     const bool is_identity = i->source == i->dest;
  33
  34     for (InjectiveMultimap::iterator j = i + 1; j != m->end(); ++j) {
  35       if (!is_identity && i->dest == j->source) {
  36         if (temp_fd == -1) {
  37           if (!delegate->Duplicate(&temp_fd, i->dest))
  38             return false;
  39           if (next_extra_fd < kMaxExtraFDs) {
  40             extra_fds[next_extra_fd++] = temp_fd;
  41           } else {
  42             RAW_LOG(ERROR, "PerformInjectiveMultimapDestructive overflowed "
  43                            "extra_fds. Leaking file descriptors!");
  44           }
  45         }
  46
  47         j->source = temp_fd;
  48         j->close = false;
  49       }
  50
  51       if (i->close && i->source == j->dest)
  52         i->close = false;
  53
  54       if (i->close && i->source == j->source) {
  55         i->close = false;
  56         j->close = true;
  57       }
  58     }
  59
  60     if (!is_identity) {
  61       if (!delegate->Move(i->source, i->dest))
  62         return false;
  63     }
  64
  65     if (!is_identity && i->close)
  66       delegate->Close(i->source);
  67   }
  68
  69   for (unsigned i = 0; i < next_extra_fd; i++)
  70     delegate->Close(extra_fds[i]);
  71
  72   return true;
  73 }
  74
  75 bool PerformInjectiveMultimap(const InjectiveMultimap& m_in,
  76                               InjectionDelegate* delegate) {
  77   InjectiveMultimap m(m_in);
  78   return PerformInjectiveMultimapDestructive(&m, delegate);
  79 }
  80
  81 bool FileDescriptorTableInjection::Duplicate(int* result, int fd) {
  82   *result = HANDLE_EINTR(dup(fd));
  83   return *result >= 0;
  84 }
  85
  86 bool FileDescriptorTableInjection::Move(int src, int dest) {
  87   return HANDLE_EINTR(dup2(src, dest)) != -1;
  88 }
  89
  90 void FileDescriptorTableInjection::Close(int fd) {
  91   int ret = HANDLE_EINTR(close(fd));
  92   DPCHECK(ret == 0);
  93 }
  94
  95 }  // namespace base