Bug: Unlimited recursion when parsing linked sections

[pd-fkie]

When the class ELFFile parses sections that are linked via sh_link it doesn't check for any loops
in the linked list.
According to Oracles Linker and Libraries Guide a linked list of sections can be terminated by
a section that points to itself if sh_flags contains the flag SHF_ORDERED.
In the current state of pyelftools however such an endless loop would result in a RecursionError exception.

The following ELF file can trigger the exception when parsed with the current version of pyelftools:
crash-d08fc9a817c40b3c241a163d9101ab425fe31db5
As the name indicates this bug was found through fuzzing and thus the crash file does not adhere to the ELF standard however it would be possible to create a valid ELF file that triggers the same exception.

[eliben]

Thanks for the report. PRs to fix this are welcome.

[sevaa]

To elaborate, the problem in the linked file is that section 0 has type SHT_HASH and has 0 as sh_link (e. g. points at itself). ELFFile.get_section() for section 0 tries to build a ELFHashSection, follows the link, which calls get_section() with 0 and so on.

[sevaa]

@pd-fkie Addressed in #522 by validating which section types can link to which.