These certificate requests also contain SHA-1 hashes, which is assumed
in `ike_cert_pre.c::process_certreq()` when enumerating key IDs.
Because the parser allocates a separate chunk for the data and the
enumerator doesn't read beyond that chunk's length after the first
iteration, only lengths between 1 and 19 are problematic (0 doesn't
cause an enumeration because chunk_empty is assigned).
Whether the OOB read then can cause a segmentation fault depends on the
allocator, its alignment rules, and its minimum overhead. For instance,
with glibc on a typical 64-bit system (8 bytes for pointers and size_t),
the alignment is 16 bytes and the minimum allocated size is 32 bytes,
with typically 24 that are technically available for data, even if only
0 bytes are allocated (as returned by `malloc_usable_size()`). So with
an allocation between 1 and 19, we can always safely read 20 bytes.
Assuming that other allocators behave similar for small allocations, it
seems unlikely that this causes a crash.
Fixes: 15612b3a42 ("Add support for IKEv2 OCSP extensions (RFC 4806)")
Tobias Brunner
4af485d87d