[ELF] Don't crash when parsing a file with external version definition references

Summary:
We were crashing when linking telnetd in FreeBSD because lld was emitting
corrupted output files for --norosegment. In this file the version index of some symbols
was set to 9 but lld only found 8 version definitions.

I am not sure how to create a minimal .so file that also exposes this behaviour so I just added the one that initially caused the error to Inputs/

This partially addresses https://bugs.llvm.org/show_bug.cgi?id=34705

Reviewers: ruiu, rafael, pcc, grimar

Reviewed By: ruiu

Subscribers: emaste, krytarowski

Tags: #lld

Differential Revision: https://reviews.llvm.org/D38397

llvm-svn: 315035

lld/ELF/InputFiles.cpp

@@ -775,9 +775,18 @@ template <class ELFT> void SharedFile<ELFT>::parseRest() {
     // Ignore local symbols.
     if (Versym && VersymIndex == VER_NDX_LOCAL)
       continue;
-
-    const Elf_Verdef *V =
-        VersymIndex == VER_NDX_GLOBAL ? nullptr : Verdefs[VersymIndex];
+    const Elf_Verdef *V = nullptr;
+    if (VersymIndex != VER_NDX_GLOBAL) {
+      if (VersymIndex >= Verdefs.size()) {
+        error("corrupt input file: version definition index " +
+              Twine(VersymIndex) + " for symbol " + Name +
+              " is greater than the maximum value " +
+              Twine(Verdefs.size() - 1) + "\n>>> symbol is defined in " +
+              toString(this));
+        continue;
+      }
+      V = Verdefs[VersymIndex];
+    }
 
     if (!Hidden)
       Symtab->addShared(Name, this, Sym, V);