[Bitcode] Prevent OOB read for invalid name size

Author: nikic

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -3243,6 +3243,8 @@ Error BitcodeReader::parseComdatRecord(ArrayRef<uint64_t> Record) {
     if (Record.size() < 2)
       return error("Invalid record");
     unsigned ComdatNameSize = Record[1];
+    if (ComdatNameSize > Record.size() - 2)
+      return error("Comdat name size too large");
     OldFormatName.reserve(ComdatNameSize);
     for (unsigned i = 0; i != ComdatNameSize; ++i)
       OldFormatName += (char)Record[2 + i];

llvm/test/Bitcode/Inputs/comdat-name-too-large.bc

@@ -271,3 +271,8 @@ RUN: not llvm-dis -disable-output %p/Inputs/unterminated-vbr.bc 2>&1 | \
 RUN:   FileCheck --check-prefix=UNTERMINATED-VBR %s
 
 UNTERMINATED-VBR: Unterminated VBR
+
+RUN: not llvm-dis -disable-output %p/Inputs/comdat-name-too-large.bc 2>&1 | \
+RUN:   FileCheck --check-prefix=COMDAT-NAME-TOO-LARGE %s
+
+COMDAT-NAME-TOO-LARGE: Comdat name size too large