[llvm] [llvm-objdump][ELF]Fix crash when reading strings from .dynstr (PR #125679)

[James Henderson via llvm-commits]

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@@ -221,6 +221,28 @@ template <class ELFT> void ELFDumper<ELFT>::printDynamicSection() {
   std::string TagFmt = "  %-" + std::to_string(MaxLen) + "s ";
 
   outs() << "\nDynamic Section:\n";
+  typename ELFT::Xword StringTableSize{0};
+  for (const typename ELFT::Shdr &Sec : cantFail(Elf.sections())) {
+    if (Sec.sh_type == ELF::SHT_DYNSYM) {
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jh7370 wrote:

Yeah, exactly. I think the core of this PR is to fix that function and add a simple check against the size of the returned `StringRef` when determining what to print for `DT_NEEDED` etc.

To minimise changes, I think I'd switch from `SHT_DYNSYM` to `SHT_DYNAMIC` in a separate PR that immediately follows this one. You might need to change the test after that change, but that's okay.

You should use `DT_STRSZ` to specify the size ONLY when the string table is found via `DT_STRTAB`. You should use the section size ONLY when the string table is found via the sections. These should only be used within `getDynamicStrTab` and then the code that calls it simply uses the returned `StringRef::size` to check the section offsets. Within `getDynamicStrTab`, you can sanity check that the `DT_STRSZ`/section `sh_size` fields (as appropriate) make sense (point within the range of the file) and return an Error from the function if they don't. That check could be a separate change, with additional testing. This PR should be about checking that the DT_* offsets are sensible.

https://github.com/llvm/llvm-project/pull/125679