[DWARF] Use forward_list in place of SmallVector to fix use-after-free issue

[MaskRay]

Summary

SmallVector's elements are moved when resizing and cause use-after-free.

[MaskRay]

Use deque

[dblaikie]

Thanks!

lib/DebugInfo/DWARF/DWARFContext.cpp

51

Remove this/replace with <deque>?

[MaskRay]

include <deque>

lib/DebugInfo/DWARF/DWARFContext.cpp

 #include "llvm/Support/Format.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cstdint>
+#include <deque>
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
 
 using namespace llvm;
 using namespace dwarf;
 using namespace object;
class DWARFObjInMemory final : public DWARFObject {
   StringRef AbbrevDWOSection;
   StringRef StringDWOSection;
   StringRef GnuPubTypesSection;
   StringRef CUIndexSection;
   StringRef GdbIndexSection;
   StringRef TUIndexSection;
   StringRef LineStringSection;
 
-  SmallVector<SmallString<32>, 4> UncompressedSections;
+  // A deque holding section data whose iterators are not invalidated when
+  // new decompressed sections are inserted at the end.
+  std::deque<SmallString<0>> UncompressedSections;
 
   StringRef *mapSectionToMember(StringRef Name) {
     if (DWARFSection *Sec = mapNameToDWARFSection(Name))
       return &Sec->Data;
     return StringSwitch<StringRef *>(Name)
         .Case("debug_abbrev", &AbbrevSection)
         .Case("debug_aranges", &ARangeSection)
         .Case("debug_frame", &DebugFrameSection)
Error maybeDecompress(const object::SectionRef &Sec, StringRef Name,
     if (!Decompressor::isCompressed(Sec))
       return Error::success();
 
     Expected<Decompressor> Decompressor =
         Decompressor::create(Name, Data, IsLittleEndian, AddressSize == 8);
     if (!Decompressor)
       return Decompressor.takeError();
 
-    SmallString<32> Out;
+    SmallString<0> Out;
     if (auto Err = Decompressor->resizeAndDecompress(Out))
       return Err;
 
-    UncompressedSections.emplace_back(std::move(Out));
+    UncompressedSections.push_back(std::move(Out));
     Data = UncompressedSections.back();
 
     return Error::success();
   }
 
 public:
   DWARFObjInMemory(const StringMap<std::unique_ptr<MemoryBuffer>> &Sections,
                    uint8_t AddrSize, bool IsLittleEndian)