[Object][ELF] Ensure offset to locate dyn section does not go past size

Validate `p_offset` in `dynamicEntries` before computing the entry offset.

Fixes: llvm#85568.

Author: antoniofrighetto

llvm/lib/Object/ELF.cpp

@@ -560,7 +560,11 @@ Expected<typename ELFT::DynRange> ELFFile<ELFT>::dynamicEntries() const {
 
   for (const Elf_Phdr &Phdr : *ProgramHeadersOrError) {
     if (Phdr.p_type == ELF::PT_DYNAMIC) {
-      Dyn = ArrayRef(reinterpret_cast<const Elf_Dyn *>(base() + Phdr.p_offset),
+      const uint8_t *DynOffset = base() + Phdr.p_offset;
+      if (DynOffset > end())
+        return createError(
+            "dynamic section offset past file size: corrupted ELF");
+      Dyn = ArrayRef(reinterpret_cast<const Elf_Dyn *>(DynOffset),
                      Phdr.p_filesz / sizeof(Elf_Dyn));
       break;
     }