Avoid a potential race between stat() and open() of ASTFile

We need to open an ASTFile while checking its expected size and
modification time, or another clang instance can modify the file between
the stat() and the open().

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207735 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Serialization/ModuleManager.cpp b/lib/Serialization/ModuleManager.cpp
index c36d902deb7f651a207ca67aa4ea9d86bb36c163..9b3159e1705af610788e7e682f4f72fc60fe68fb 100644 (file)
--- a/lib/Serialization/ModuleManager.cpp
+++ b/lib/Serialization/ModuleManager.cpp
@@ -381,7 +381,9 @@ bool ModuleManager::lookupModuleFile(StringRef FileName,
                                      off_t ExpectedSize,
                                      time_t ExpectedModTime,
                                      const FileEntry *&File) {
-  File = FileMgr.getFile(FileName, /*openFile=*/false, /*cacheFailure=*/false);
+  // Open the file immediately to ensure there is no race between stat'ing and
+  // opening the file.
+  File = FileMgr.getFile(FileName, /*openFile=*/true, /*cacheFailure=*/false);
 
   if (!File && FileName != "-") {
     return false;
@@ -389,6 +391,8 @@ bool ModuleManager::lookupModuleFile(StringRef FileName,
 
   if ((ExpectedSize && ExpectedSize != File->getSize()) ||
       (ExpectedModTime && ExpectedModTime != File->getModificationTime())) {
+    FileMgr.invalidateCache(File);
+    File = nullptr;
     return true;
   }