Description of problem:
I created a local shared sub-network to allow secondary computer to share connections of the main computer. Connection seemed to work, but I was only able to ping the main computer from the secondary one. Pings to other system (neither local nor internet ones) did not work.

Connections from the main computer to local network and internet were functional (from the main computer). SELinux was set to enforcing mode.


Version-Release number of selected component (if applicable):
selinux-policy-34.1.18-1.el9.noarch
NetworkManager-1.34.0-0.1.el9.x86_64
nftables-0.9.8-9.el9.x86_64


How reproducible:
Always


Steps to Reproduce:
1. Have a computer (nb1) with 2 network ports (I use built-in ethernet + USB-to-ethernet adapter) and RHEL 9 installed.
2. Have nb1 connected to local network (and internet) via one of the ports. (Try "ping www.redhat.com")
3. Create a shared sub-net connection (on nb1):
nmcli connection add type ethernet con-name USB-eth-shared ipv4.method shared ipv4.addresses 192.168.81.1/24
4. Activate the shared sub-net connection on the other network port (list available ports with "ip a"):
nmcli connection up USB-eth-shared ifname <your_if_name>
5. Connect the second computer (nb2) to the second network port on nb1.
6. nb2 should get network auto-configured (DHCP) having nb1 as default gateway and you should be able to ping nb1.
7. Try "ping www.redhat.com" on nb2.


Actual results:
- New SELinux security alert appears (step 4).
- ping from nb2 to internet does not work (100 % packet loss).


Expected results:
- No SELinux alert should appear.
- ping from nb2 to internet should work.


Additional info:

Works with SELinux in permisive mode - workaround (on nb1):
1. nmcli connection down USB-eth-shared
2. sudo setenforce 0
3. nmcli connection up USB-eth-shared ifname <your_if_name>



SELinux is preventing /usr/sbin/nft from open access on the fifo_file fifo_file.

*****  Plugin catchall (100. confidence) suggests   **************************

If you believe that nft should be allowed open access on the fifo_file fifo_file by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# ausearch -c 'nft' --raw | audit2allow -M my-nft
# semodule -X 300 -i my-nft.pp

Additional Information:
Source Context                system_u:system_r:iptables_t:s0
Target Context                system_u:system_r:NetworkManager_t:s0
Target Objects                fifo_file [ fifo_file ]
Source                        nft
Source Path                   /usr/sbin/nft
Port                          <Unknown>
Host                          p3551
Source RPM Packages           nftables-0.9.8-9.el9.x86_64
Target RPM Packages           
SELinux Policy RPM            selinux-policy-targeted-34.1.18-1.el9.noarch
Local Policy RPM              selinux-policy-targeted-34.1.18-1.el9.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     p3551
Platform                      Linux p3551 5.14.0-8.el9.x86_64 #1 SMP Tue Oct 19
                              03:58:57 EDT 2021 x86_64 x86_64
Alert Count                   5
First Seen                    2021-11-12 17:26:08 CET
Last Seen                     2021-11-15 11:51:19 CET
Local ID                      39dfc045-862c-45e6-a90c-166958fa29b3

Raw Audit Messages
type=AVC msg=audit(1636973479.219:4177): avc:  denied  { open } for  pid=174956 comm="nft" path="pipe:[2186495]" dev="pipefs" ino=2186495 scontext=system_u:system_r:iptables_t:s0 tcontext=system_u:system_r:NetworkManager_t:s0 tclass=fifo_file permissive=0


type=SYSCALL msg=audit(1636973479.219:4177): arch=x86_64 syscall=openat success=no exit=EACCES a0=ffffff9c a1=7f42c61643a1 a2=0 a3=0 items=0 ppid=1750 pid=174956 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm=nft exe=/usr/sbin/nft subj=system_u:system_r:iptables_t:s0 key=(null)

Hash: nft,iptables_t,NetworkManager_t,fifo_file,open