MFC r351889:

Bounds check again after advancing cp, otherwise we have a possible
heap buffer overflow. This was discovered by a Google fuzzer test.
This can lead to remote denial of service. User interaction and
execution privileges are not a prerequisite for exploitation.

Reported by: enh at Google, to FreeBSD by maya@NetBSD.org
Obtained from: enh at Google
See also: NetBSD ns_name.c r1.12
Reviewed by: delphij, ume
MFC after: 3 days
https://android-review.googlesource.com/c/platform/bionic/+/1093130
Differential Revision: https://reviews.freebsd.org/D21523