bin/59415: group(8) can rename a group to an existing group name

[triaxx%netbsd.org@localhost]

>Number:         59415
>Category:       bin
>Synopsis:       group(8) can rename a group to an existing group name
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 10 05:30:00 +0000 2025
>Originator:     Frédéric Fauberteau
>Release:        NetBSD 10.1
>Organization:
>Environment:
System: NetBSD ghost.triaxx.online 10.1 NetBSD 10.1 (GENERIC) #0: Mon Dec 16 13:08:11 UTC 2024  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
groupmod(8) doesn't seem to check whether a new group name is already in use or not.
>How-To-Repeat:
# tail -n2 /etc/group
foo:*:1003:
bar:*:1004:

# group mod -n foo bar

# tail -n2 /etc/group
foo:*:1003:
foo:*:1004:
>Fix: