crash-reporter: Avoid writing through symlinks.

kernel_collector.cc

Index: kernel_collector.cc
diff --git a/kernel_collector.cc b/kernel_collector.cc
index c95873347dd435b1247e093fb69d0cd1623450e4..4fa51e26e7d2752e494defbca0f5e870323af38d 100644
--- a/kernel_collector.cc
+++ b/kernel_collector.cc
@@ -277,9 +277,12 @@ bool KernelCollector::Collect() {
     FilePath kernel_crash_path = root_crash_directory.Append(
         StringPrintf("%s.kcrash", dump_basename.c_str()));
 
-    if (file_util::WriteFile(kernel_crash_path,
-                             kernel_dump.data(),
-                             kernel_dump.length()) !=
+    // We must use WriteNewFile instead of file_util::WriteFile as we
+    // do not want to write with root access to a symlink that an attacker
+    // might have created.
+    if (WriteNewFile(kernel_crash_path,
+                     kernel_dump.data(),
+                     kernel_dump.length()) !=
         static_cast<int>(kernel_dump.length())) {
       logger_->LogInfo("Failed to write kernel dump to %s",
                        kernel_crash_path.value().c_str());