[Object/ELF] - Do not crash on invalid section index.

[grimar]

Summary

If object has wrong (large) string table index and
also incorrect large value for amount of sections in total,
then section index passes the check:

  if (Index >= getNumSections())
    return object_error::invalid_section_index;

But result pointer then is far after end of file data, what
result in a crash.

Patch fixes the issue.

[grimar]

Ping.

[• rafael]

LGTM

llvm/trunk/include/llvm/Object/ELF.h

 
 template <class ELFT>
 ErrorOr<const typename ELFFile<ELFT>::Elf_Shdr *>
 ELFFile<ELFT>::getSection(uint32_t Index) const {
   assert(SectionHeaderTable && "SectionHeaderTable not initialized!");
   if (Index >= getNumSections())
     return object_error::invalid_section_index;
 
-  return reinterpret_cast<const Elf_Shdr *>(
-      reinterpret_cast<const char *>(SectionHeaderTable) +
-      (Index * Header->e_shentsize));
+  const uint8_t *Addr = reinterpret_cast<const uint8_t *>(SectionHeaderTable) +
+                        (Index * Header->e_shentsize);
+  if (Addr >= base() + getBufSize())
+    return object_error::invalid_section_index;
+  return reinterpret_cast<const Elf_Shdr *>(Addr);
 }
 
 template <class ELFT>
 ErrorOr<StringRef>
 ELFFile<ELFT>::getStringTable(const Elf_Shdr *Section) const {
   if (Section->sh_type != ELF::SHT_STRTAB)
     return object_error::parse_failed;
   auto V = getSectionContentsAsArray<char>(Section);

llvm/trunk/test/Object/invalid.test

 
 RUN: not llvm-readobj -t %p/Inputs/invalid-sh_entsize.elf 2>&1 | FileCheck --check-prefix=INVALID-SYM-SIZE %s
 INVALID-SYM-SIZE: Invalid data was encountered while parsing the file
 
 RUN: not llvm-readobj --dyn-symbols %p/Inputs/invalid-sh_entsize.elf 2>&1 | FileCheck --check-prefix=INVALID-DYNSYM-SIZE %s
 INVALID-DYNSYM-SIZE: Invalid entity size
 
 RUN: not llvm-readobj -t %p/Inputs/invalid-section-index.elf 2>&1 | FileCheck --check-prefix=INVALID-SECTION-INDEX %s
-
+RUN: not llvm-readobj -t %p/Inputs/invalid-section-index2.elf 2>&1 | FileCheck --check-prefix=INVALID-SECTION-INDEX %s
 INVALID-SECTION-INDEX: Invalid section index
 
 RUN: not llvm-readobj -s %p/Inputs/invalid-section-size.elf 2>&1 | FileCheck --check-prefix=INVALID-SECTION-SIZE %s
 INVALID-SECTION-SIZE: Invalid section header entry size (e_shentsize) in ELF header
 
 
 RUN: not llvm-readobj -t %p/Inputs/invalid-symbol-table-size.elf 2>&1 | FileCheck --check-prefix=INVALID-SYMTAB-SIZE %s
 INVALID-SYMTAB-SIZE: Invalid data was encountered while parsing the file