[clang] Reject character devices in #embed for now (#135370)

See #126629 . Right now they
are not supported properly and support requires modifying several layers
of LLVM. For now simply reject them while proper support is being
developed to avoid potential security problems.

Author: Fznamznon

clang/docs/ReleaseNotes.rst

@@ -398,6 +398,9 @@ Bug Fixes in This Version
 
     #if 1 ? 1 : 999999999999999999999
     #endif
+- ``#embed`` directive now diagnoses use of a non-character file (device file)
+  such as ``/dev/urandom`` as an error. This restriction may be relaxed in the
+  future. See (#GH126629).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -458,6 +458,8 @@ def warn_compat_pp_embed_directive : Warning<
   InGroup<CPre23Compat>, DefaultIgnore;
 def err_pp_embed_dup_params : Error<
   "cannot specify parameter '%0' twice in the same '#embed' directive">;
+def err_pp_embed_device_file : Error<
+  "device files are not yet supported by '#embed' directive">;
 
 def ext_pp_extra_tokens_at_eol : ExtWarn<
   "extra tokens at end of #%0 directive">, InGroup<ExtraTokens>;

clang/include/clang/Basic/FileEntry.h

@@ -82,6 +82,7 @@ class FileEntryRef {
   inline const llvm::sys::fs::UniqueID &getUniqueID() const;
   inline time_t getModificationTime() const;
   inline bool isNamedPipe() const;
+  inline bool isDeviceFile() const;
   inline void closeFile() const;
 
   /// Check if the underlying FileEntry is the same, intentially ignoring
@@ -316,6 +317,7 @@ class FileEntry {
   llvm::sys::fs::UniqueID UniqueID;
   unsigned UID = 0; // A unique (small) ID for the file.
   bool IsNamedPipe = false;
+  bool IsDeviceFile = false;
 
   /// The open file, if it is owned by the \p FileEntry.
   mutable std::unique_ptr<llvm::vfs::File> File;
@@ -340,6 +342,7 @@ class FileEntry {
   /// Check whether the file is a named pipe (and thus can't be opened by
   /// the native FileManager methods).
   bool isNamedPipe() const { return IsNamedPipe; }
+  bool isDeviceFile() const { return IsDeviceFile; }
 
   void closeFile() const;
 };
@@ -357,6 +360,9 @@ time_t FileEntryRef::getModificationTime() const {
 }
 
 bool FileEntryRef::isNamedPipe() const { return getFileEntry().isNamedPipe(); }
+bool FileEntryRef::isDeviceFile() const {
+  return getFileEntry().isDeviceFile();
+}
 
 void FileEntryRef::closeFile() const { getFileEntry().closeFile(); }
 

clang/lib/Basic/FileManager.cpp

@@ -330,6 +330,8 @@ llvm::Expected<FileEntryRef> FileManager::getFileRef(StringRef Filename,
   UFE->UID = NextFileUID++;
   UFE->UniqueID = Status.getUniqueID();
   UFE->IsNamedPipe = Status.getType() == llvm::sys::fs::file_type::fifo_file;
+  UFE->IsDeviceFile =
+      Status.getType() == llvm::sys::fs::file_type::character_file;
   UFE->File = std::move(F);
 
   if (UFE->File) {

clang/lib/Lex/PPDirectives.cpp

@@ -4012,6 +4012,12 @@ void Preprocessor::HandleEmbedDirective(SourceLocation HashLoc, Token &EmbedTok,
     Diag(FilenameTok, diag::err_pp_file_not_found) << Filename;
     return;
   }
+
+  if (MaybeFileRef->isDeviceFile()) {
+    Diag(FilenameTok, diag::err_pp_embed_device_file) << Filename;
+    return;
+  }
+
   std::optional<llvm::MemoryBufferRef> MaybeFile =
       getSourceManager().getMemoryBufferForFileOrNone(*MaybeFileRef);
   if (!MaybeFile) {

clang/test/Preprocessor/embed-reject-device-files-lin.c

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -std=c23 %s -fsyntax-only -verify
+// REQUIRES: system-linux
+
+
+int urandom[] = {
+#embed "/dev/urandom" //expected-error {{device files are not yet supported by '#embed' directive}}
+};
+int random[] = {
+#embed "/dev/random" //expected-error {{device files are not yet supported by '#embed' directive}}
+};
+int zero[] = {
+#embed "/dev/zero" //expected-error {{device files are not yet supported by '#embed' directive}}
+};
+int null[] = {
+#embed "/dev/null" //expected-error {{device files are not yet supported by '#embed' directive}}
+};

clang/test/Preprocessor/embed-reject-device-files-win.c

@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -std=c23 %s -fsyntax-only -verify
+// REQUIRES: system-windows
+
+
+int null[] = {
+#embed "NUL" limit(1) //expected-error {{device files are not yet supported by '#embed' directive}}
+};