netfilter: nf_conntrack_ipv4 does not show nf_nat as a user

https://bugzilla.redhat.com/show_bug.cgi?id=333481#c3

This is netfilter kernel problem. There is a usage count for the conntrack_ipv4 module from the nf_nat module, which is not reported by lsmod.

How to reproduce:

# modprobe nf_conntrack_ipv4
# lsmod | grep nf_conntrack_ipv4
nf_conntrack_ipv4      11717  0 
nf_conntrack           51977  2 nf_conntrack_ipv4,nf_conntrack_ipv6
nfnetlink               8281  3 nf_conntrack_ipv4,nf_conntrack_ipv6,nf_conntrack
# modprobe nf_nat
# lsmod | grep nf_conntrack_ipv4
nf_conntrack_ipv4      11717  1 
nf_conntrack           51977  3 nf_nat,nf_conntrack_ipv4,nf_conntrack_ipv6
nfnetlink               8281  4 nf_nat,nf_conntrack_ipv4,nf_conntrack_ipv6,nf_co
nntrack
# lsmod | grep nf_nat
nf_nat                 18669  0 
nf_conntrack           51977  3 nf_nat,nf_conntrack_ipv4,nf_conntrack_ipv6
nfnetlink               8281  4 nf_nat,nf_conntrack_ipv4,nf_conntrack_ipv6,nf_co
nntrack
# rmmod nf_conntrack_ipv4
ERROR: Module nf_conntrack_ipv4 is in use
# rmmod nf_nat
# rmmod nf_conntrack_ipv4

This is "fixed" in the current kernel.

By this hack?

[NETFILTER]: Fix/improve deadlock condition on module removal netfilter

Thats not really a hack, the patch is fully correct, the bug was in modutils.

The patch I'm talking about is 591e6206:

[NETFILTER]: nf_nat: add symbolic dependency on IPv4 conntrack