[Object/ELF] - Do check for invalid section header entry size earlier.

[grimar]

Summary

Zero value in e_shentsize was the reason of crash in lld.
When we have zero size and huge amount of sections,
resize() in below code could fail.

template <class ELFT>
void elf::ObjectFile<ELFT>::initializeSections(
    DenseSet<StringRef> &ComdatGroups) {
  uint64_t Size = this->ELFObj.getNumSections();
  Sections.resize(Size);

No any new testcase as this fatal message is already has one.

[grimar]

Ping.

[grimar]

I'll revisit this one to find more localized fix.

ELF.h

ELFFile<ELFT>::ELFFile(StringRef Object, std::error_code &EC)
   const uint64_t SectionTableOffset = Header->e_shoff;
 
   if (SectionTableOffset + sizeof(Elf_Shdr) > FileSize) {
     // Section header table goes past end of file!
     EC = object_error::parse_failed;
     return;
   }
 
+  if (Header->e_shentsize != sizeof(Elf_Shdr))
+    report_fatal_error(
+        "Invalid section header entry size (e_shentsize) in ELF header");
+
   // The getNumSections() call below depends on SectionHeaderTable being set.
   SectionHeaderTable =
     reinterpret_cast<const Elf_Shdr *>(base() + SectionTableOffset);
   const uint64_t SectionTableSize = getNumSections() * Header->e_shentsize;
 
   if (SectionTableOffset + SectionTableSize > FileSize) {
     // Section table goes past end of file!
     EC = object_error::parse_failed;

 
 template <class ELFT>
 static bool compareAddr(uint64_t VAddr, const Elf_Phdr_Impl<ELFT> *Phdr) {
   return VAddr < Phdr->p_vaddr;
 }
 
 template <class ELFT>
 const typename ELFFile<ELFT>::Elf_Shdr *ELFFile<ELFT>::section_begin() const {
-  if (Header->e_shentsize != sizeof(Elf_Shdr))
-    report_fatal_error(
-        "Invalid section header entry size (e_shentsize) in ELF header");
   return reinterpret_cast<const Elf_Shdr *>(base() + Header->e_shoff);
 }
 
 template <class ELFT>
 const typename ELFFile<ELFT>::Elf_Shdr *ELFFile<ELFT>::section_end() const {
   return section_begin() + getNumSections();
 }