[Object/ELF] - Report error on incorrect sh_offset.

[grimar]

Summary

It is related with PR30540, previously if sh_offset was incorrect (too large),
returned pointer could be wrong.

It is not possible to craft file with incorrect sh_offset using yaml2obj it seems,
so used precompiled one.

[davide]

did you try to minimize this? afl has an utility for that (afl-min) you may want to check out.

[grimar]

In D25015#555336, @davide wrote:

did you try to minimize this? afl has an utility for that (afl-min) you may want to check out.

I tried. No reduce of file size for this testcase, so leaved it as is.

[grimar]

• Rebased.

[grimar]

r283454 fixed that.

include/llvm/Object/ELF.h

Elf_Shdr_Range sections() const {
     return makeArrayRef(section_begin(), section_end());
   }
 
   const Elf_Sym *symbol_begin(const Elf_Shdr *Sec) const {
     if (!Sec)
       return nullptr;
     if (Sec->sh_entsize != sizeof(Elf_Sym))
       report_fatal_error("Invalid symbol size");
+    if (Sec->sh_offset >= Buf.size())
+      report_fatal_error("Invalid symbol offset");
     return reinterpret_cast<const Elf_Sym *>(base() + Sec->sh_offset);
   }
   const Elf_Sym *symbol_end(const Elf_Shdr *Sec) const {
     if (!Sec)
       return nullptr;
     uint64_t Size = Sec->sh_size;
     if (Size % sizeof(Elf_Sym))
       report_fatal_error("Invalid symbol table size");

test/Object/invalid.test

 SECTION-NEXT:    Link:
 SECTION-NEXT:    Info:
 SECTION-NEXT:    AddressAlignment:
 SECTION-NEXT:    EntrySize: 32
 
 RUN: not llvm-readobj -t %p/Inputs/invalid-sh_entsize.elf 2>&1 | FileCheck --check-prefix=INVALID-SYM-SIZE %s
 INVALID-SYM-SIZE: Invalid symbol size
 
+RUN: not llvm-readobj -t %p/Inputs/invalid-sh_offset.elf 2>&1 | FileCheck --check-prefix=INVALID-SYM-OFFSET %s
+INVALID-SYM-OFFSET: Invalid symbol offset
+
 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
 
 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