base/file_descriptor_shuffle.cc

   1 // Copyright (c) 2011 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 <unistd.h>
   8 #include <stddef.h>
   9 #include <ostream>
  10
  11 #include "base/eintr_wrapper.h"
  12 #include "base/logging.h"
  13
  14 namespace base {
  15
  16 bool PerformInjectiveMultimapDestructive(
  17     InjectiveMultimap* m, InjectionDelegate* delegate) {
  18   static const size_t kMaxExtraFDs = 16;
  19   int extra_fds[kMaxExtraFDs];
  20   unsigned next_extra_fd = 0;
  21
  22   // DANGER: this function may not allocate.
  23
  24   for (InjectiveMultimap::iterator i = m->begin(); i != m->end(); ++i) {
  25     int temp_fd = -1;
  26
  27     // We DCHECK the injectiveness of the mapping.
  28     for (InjectiveMultimap::iterator j = i + 1; j != m->end(); ++j) {
  29       DCHECK(i->dest != j->dest) << "Both fd " << i->source
  30           << " and " << j->source << " map to " << i->dest;
  31     }
  32
  33     const bool is_identity = i->source == i->dest;
  34
  35     for (InjectiveMultimap::iterator j = i + 1; j != m->end(); ++j) {
  36       if (!is_identity && i->dest == j->source) {
  37         if (temp_fd == -1) {
  38           if (!delegate->Duplicate(&temp_fd, i->dest))
  39             return false;
  40           if (next_extra_fd < kMaxExtraFDs) {
  41             extra_fds[next_extra_fd++] = temp_fd;
  42           } else {
  43             RAW_LOG(ERROR, "PerformInjectiveMultimapDestructive overflowed "
  44                            "extra_fds. Leaking file descriptors!");
  45           }
  46         }
  47
  48         j->source = temp_fd;
  49         j->close = false;
  50       }
  51
  52       if (i->close && i->source == j->dest)
  53         i->close = false;
  54
  55       if (i->close && i->source == j->source) {
  56         i->close = false;
  57         j->close = true;
  58       }
  59     }
  60
  61     if (!is_identity) {
  62       if (!delegate->Move(i->source, i->dest))
  63         return false;
  64     }
  65
  66     if (!is_identity && i->close)
  67       delegate->Close(i->source);
  68   }
  69
  70   for (unsigned i = 0; i < next_extra_fd; i++)
  71     delegate->Close(extra_fds[i]);
  72
  73   return true;
  74 }
  75
  76 bool PerformInjectiveMultimap(const InjectiveMultimap& m_in,
  77                               InjectionDelegate* delegate) {
  78   InjectiveMultimap m(m_in);
  79   return PerformInjectiveMultimapDestructive(&m, delegate);
  80 }
  81
  82 bool FileDescriptorTableInjection::Duplicate(int* result, int fd) {
  83   *result = HANDLE_EINTR(dup(fd));
  84   return *result >= 0;
  85 }
  86
  87 bool FileDescriptorTableInjection::Move(int src, int dest) {
  88   return HANDLE_EINTR(dup2(src, dest)) != -1;
  89 }
  90
  91 void FileDescriptorTableInjection::Close(int fd) {
  92   int ret = HANDLE_EINTR(close(fd));
  93   DPCHECK(ret == 0);
  94 }
  95
  96 }  // namespace base