[BitcodeReader] Use tighter upper bound to validate forward references.

At the moment, bitcode files with invalid forward reference can easily
cause the bitcode reader to run out of memory, by creating a forward
reference with a very high index.

We can use the size of the bitcode file as an upper bound, because a
valid bitcode file can never contain more records. This should be
sufficient to fail early in most cases. The only exception is large
files with invalid forward references close to the file size.

There are a couple of clusterfuzz runs that fail with out-of-memory
because of very high forward references and they should be fixed by this
patch.

A concrete example for this is D64507, which causes out-of-memory on
systems with low memory, like the hexagon upstream bots.

Reviewers: t.p.northover, thegameg, jfb, efriedma, hfinkel

Reviewed By: jfb

Differential Revision: https://reviews.llvm.org/D64577

llvm-svn: 366017

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Reader/ValueList.cpp b/llvm/lib/Bitcode/Reader/ValueList.cpp
index da2d24d103b..431995fd40a 100644
--- a/llvm/lib/Bitcode/Reader/ValueList.cpp
+++ b/llvm/lib/Bitcode/Reader/ValueList.cpp
@@ -97,6 +97,10 @@ void BitcodeReaderValueList::assignValue(Value *V, unsigned Idx, Type *FullTy) {
 }
 
 Constant *BitcodeReaderValueList::getConstantFwdRef(unsigned Idx, Type *Ty) {
+  // Bail out for a clearly invalid value.
+  if (Idx >= RefsUpperBound)
+    return nullptr;
+
   if (Idx >= size())
     resize(Idx + 1);
 
@@ -114,8 +118,8 @@ Constant *BitcodeReaderValueList::getConstantFwdRef(unsigned Idx, Type *Ty) {
 
 Value *BitcodeReaderValueList::getValueFwdRef(unsigned Idx, Type *Ty,
                                               Type **FullTy) {
-  // Bail out for a clearly invalid value. This would make us call resize(0)
-  if (Idx == std::numeric_limits<unsigned>::max())
+  // Bail out for a clearly invalid value.
+  if (Idx >= RefsUpperBound)
     return nullptr;
 
   if (Idx >= size())