POSIX: don't allocate memory after forking.

base/file_descriptor_shuffle.cc

Index: base/file_descriptor_shuffle.cc
diff --git a/base/file_descriptor_shuffle.cc b/base/file_descriptor_shuffle.cc
index e722a29e89fc5f3f0b646fbbef4188550ae68c51..2bb156bf3c7d5005cd55242744f6e5e0d5f0e38e 100644
--- a/base/file_descriptor_shuffle.cc
+++ b/base/file_descriptor_shuffle.cc
@@ -12,28 +12,36 @@
 
 namespace base {
 
-bool PerformInjectiveMultimap(const InjectiveMultimap& m_in,
-                              InjectionDelegate* delegate) {
-  InjectiveMultimap m(m_in);
-  std::vector<int> extra_fds;
+bool PerformInjectiveMultimapDestructive(
+    InjectiveMultimap* m, InjectionDelegate* delegate) {
+  static const size_t kMaxExtraFDs = 16;
+  int extra_fds[kMaxExtraFDs];
+  unsigned next_extra_fd = 0;
 
-  for (InjectiveMultimap::iterator i = m.begin(); i != m.end(); ++i) {
+  // DANGER: this function may not allocate.
+
+  for (InjectiveMultimap::iterator i = m->begin(); i != m->end(); ++i) {
     int temp_fd = -1;
 
     // We DCHECK the injectiveness of the mapping.
-    for (InjectiveMultimap::iterator j = i + 1; j != m.end(); ++j) {
+    for (InjectiveMultimap::iterator j = i + 1; j != m->end(); ++j) {
       DCHECK(i->dest != j->dest) << "Both fd " << i->source
           << " and " << j->source << " map to " << i->dest;
     }
 
     const bool is_identity = i->source == i->dest;
 
-    for (InjectiveMultimap::iterator j = i + 1; j != m.end(); ++j) {
+    for (InjectiveMultimap::iterator j = i + 1; j != m->end(); ++j) {
       if (!is_identity && i->dest == j->source) {
         if (temp_fd == -1) {
           if (!delegate->Duplicate(&temp_fd, i->dest))
             return false;
-          extra_fds.push_back(temp_fd);
+          if (next_extra_fd < kMaxExtraFDs) {
+            extra_fds[next_extra_fd++] = temp_fd;
+          } else {
+            RAW_LOG(ERROR, "PerformInjectiveMultimapDestructive overflowed "
+                           "extra_fds. Leaking file descriptors!");
+          }
         }
 
         j->source = temp_fd;
@@ -58,14 +66,18 @@ bool PerformInjectiveMultimap(const InjectiveMultimap& m_in,
       delegate->Close(i->source);
   }
 
-  for (std::vector<int>::const_iterator
-       i = extra_fds.begin(); i != extra_fds.end(); ++i) {
-    delegate->Close(*i);
-  }
+  for (unsigned i = 0; i < next_extra_fd; i++)
+    delegate->Close(extra_fds[i]);
 
   return true;
 }
 
+bool PerformInjectiveMultimap(const InjectiveMultimap& m_in,
+                              InjectionDelegate* delegate) {
+  InjectiveMultimap m(m_in);
+  return PerformInjectiveMultimapDestructive(&m, delegate);
+}
+
 bool FileDescriptorTableInjection::Duplicate(int* result, int fd) {
   *result = HANDLE_EINTR(dup(fd));
   return *result >= 0;