[Linux] Do not try to call readdir() on a null DIR* in base::ProcessIterator.

base/process/process_iterator_linux.cc

 // Copyright (c) 2013 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 "base/process/process_iterator.h"
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/process/internal_linux.h"
 #include "base/strings/string_split.h"
@@ skipping 41 matching lines @@
   *proc_cmd_line_args = SplitString(cmd_line, delimiters, KEEP_WHITESPACE,
                                     SPLIT_WANT_NONEMPTY);
   return true;
 }
 
 }  // namespace
 
 ProcessIterator::ProcessIterator(const ProcessFilter* filter)
     : filter_(filter) {
   procfs_dir_ = opendir(internal::kProcDir);
+  if (!procfs_dir_) {
+    // On Android, SELinux may prevent reading /proc. See
+    // https://crbug.com/581517 for details.
+    PLOG(ERROR) << "opendir " << internal::kProcDir;
+  }
 }
 
 ProcessIterator::~ProcessIterator() {
   if (procfs_dir_) {
     closedir(procfs_dir_);
-    procfs_dir_ = NULL;
+    procfs_dir_ = nullptr;
   }
 }
 
 bool ProcessIterator::CheckForNextProcess() {
   // TODO(port): skip processes owned by different UID
 
+  if (!procfs_dir_) {
+    DLOG(ERROR) << "Skipping CheckForNextProcess(), no procfs_dir_";
+    return false;
+  }
+
   pid_t pid = kNullProcessId;
   std::vector<std::string> cmd_line_args;
   std::string stats_data;
   std::vector<std::string> proc_stats;
 
   // Arbitrarily guess that there will never be more than 200 non-process
   // files in /proc.  Hardy has 53 and Lucid has 61.
   int skipped = 0;
   const int kSkipLimit = 200;
   while (skipped < kSkipLimit) {
@@ skipping 46 matching lines @@
   return true;
 }
 
 bool NamedProcessIterator::IncludeEntry() {
   if (executable_name_ != entry().exe_file())
     return false;
   return ProcessIterator::IncludeEntry();
 }
 
 }  // namespace base