Comment # 1 on bug 1047890 from Johannes Meixner

On my Leap 42.1 system it looks o.k.:
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# rpm -q cups
cups-2.2.3-210.1.x86_64

# rpm -V cups
S.5....T.  c /etc/cups/cups-files.conf
S.5....T.  c /etc/cups/cupsd.conf

# for f in $( rpm -ql cups | grep /usr/lib/cups/backend/ ) ; do ls -l $f ; done
-rwx------ 1 root root ... /usr/lib/cups/backend/dnssd
lrwxrwxrwx 1 root root ... /usr/lib/cups/backend/http -> ipp
lrwxrwxrwx 1 root root ... /usr/lib/cups/backend/https -> ipp
-rwx------ 1 root root ... /usr/lib/cups/backend/ipp
lrwxrwxrwx 1 root root ... /usr/lib/cups/backend/ipps -> ipp
-rwx------ 1 root root ... /usr/lib/cups/backend/lpd
-r-xr-xr-x 1 root root ... /usr/lib/cups/backend/snmp
-r-xr-xr-x 1 root root ... /usr/lib/cups/backend/socket
-r-xr-xr-x 1 root root ... /usr/lib/cups/backend/usb

root@10.160.4.251# netcat -l -p 1234

# lpadmin -p sockettest -v socket://10.160.4.251:1234 -E

# echo Hello | lp -d sockettest
request id is sockettest-8438 (0 file(s))

On 10.160.4.251 where 'netcat' runs, "Hello" appears.

# grep PID /var/log/cups/error_log
...
I ... [Job 8438] Started backend /usr/lib/cups/backend/socket (PID 9332)
D ... [Job 8438] PID 9332 (/usr/lib/cups/backend/socket) exited with no errors.
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FYI:

Since years cupsd runs as root, not as lp, cf.
https://en.opensuse.org/SDB:CUPS_in_a_Nutshell
(excerpt):
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For example RunAsUser is no longer supported so that
since openSUSE 10.2 / CUPS 1.2 the cupsd runs as root
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cups-2.2.3/backend/Makefile:127 should be meaningless because
the files in a RPM package are installed with those user, group,
and permissions that are specified in the RPM spec file.