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().

llvm-svn: 207735

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/Serialization/ModuleManager.cpp b/clang/lib/Serialization/ModuleManager.cpp
index c36d902deb7..9b3159e1705 100644
--- a/clang/lib/Serialization/ModuleManager.cpp
+++ b/clang/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;
   }