Existing code checks that the first uint64_t ctfa_magic field is
available before reading but neglects to check that the last uint64_t
ctfa_ctfs is available before reading it in ctf_arc_bufpreamble.
ctf_arc_bufopen sets up a pointer to the struct ctf_archive in
ctf_new_archive_internal. Extend the check to cover the entire struct.
PR 33548
PR 33549
* ctf-archive.c (ctf_arc_bufpreamble, ctf_arc_bufopen): Check
that buffer contains at least an entire struct ctf_archive
when accessing such a struct.
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