mpatch.c
in Mercurial before 4.6.1 mishandles integer addition and subtraction, aka OVE-20180430-0002.
access.redhat.com/errata/RHSA-2019:2276
github.com/advisories/GHSA-3mjj-mr4f-qxmx
lists.debian.org/debian-lts-announce/2020/07/msg00032.html
nvd.nist.gov/vuln/detail/CVE-2018-13347
www.mercurial-scm.org/repo/hg-committed/log?rev=modifies%28%22mercurial%2Fmpatch.c%22%29+and+4.5%3A%3A
www.mercurial-scm.org/repo/hg/rev/1acfc35d478c
www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.6.1_.282018-06-06.29