commit 50934a243e4986c2d7f31dc85b24ae73d4e94db0
Author: Lukas Vrabec <lvrabec>
Date:   Sun Mar 1 13:08:42 2015 +0100

    Allow denyhosts execute iptables. BZ(1197371)

selinux-policy-3.13.1-105.6.fc21 has been submitted as an update for Fedora 21.
https://admin.fedoraproject.org/updates/selinux-policy-3.13.1-105.6.fc21

Package selinux-policy-3.13.1-105.6.fc21:
* should fix your issue,
* was pushed to the Fedora 21 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing selinux-policy-3.13.1-105.6.fc21'
as soon as you are able to.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2015-3476/selinux-policy-3.13.1-105.6.fc21
then log in and leave karma (feedback).

Looks like it helped with the main problem (I'm getting new entries in iptables now), but there's a new alert with several audit messages.

I don't get why iptables would want to write to denyhosts' files but there you go:


SELinux is preventing /usr/sbin/xtables-multi from 'write' accesses on the file /run/lock/subsys/denyhosts.

Additional Information:
Source Context                system_u:system_r:iptables_t:s0
Target Context                system_u:object_r:denyhosts_var_lock_t:s0
Target Objects                /run/lock/subsys/denyhosts [ file ]
Source                        iptables
Source Path                   /usr/sbin/xtables-multi
Port                          <Unknown>
Host                          (removed)
Source RPM Packages           iptables-1.4.21-13.fc21.x86_64
Target RPM Packages           
Policy RPM                    selinux-policy-3.13.1-105.6.fc21.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     (removed)
Platform                      Linux (removed) 3.18.8-201.fc21.x86_64 #1 SMP Fri
                              Feb 27 18:18:27 UTC 2015 x86_64 x86_64
Alert Count                   1
First Seen                    2015-03-10 14:00:56 CET
Last Seen                     2015-03-10 14:00:56 CET
Local ID                      2b946b32-cbff-4359-b926-4e89128d0709

Raw Audit Messages
type=AVC msg=audit(1425992456.826:3216): avc:  denied  { write } for  pid=9310 comm="iptables" path="/run/lock/subsys/denyhosts" dev="tmpfs" ino=18514 scontext=system_u:system_r:iptables_t:s0 tcontext=system_u:object_r:denyhosts_var_lock_t:s0 tclass=file permissive=0


type=AVC msg=audit(1425992456.826:3216): avc:  denied  { append } for  pid=9310 comm="iptables" path="/etc/hosts.deny" dev="md127" ino=27788257 scontext=system_u:system_r:iptables_t:s0 tcontext=system_u:object_r:net_conf_t:s0 tclass=file permissive=0


type=SYSCALL msg=audit(1425992456.826:3216): arch=x86_64 syscall=execve success=yes exit=0 a0=a9ced0 a1=a9cfb0 a2=a9bb20 a3=51 items=0 ppid=780 pid=9310 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm=iptables exe=/usr/sbin/xtables-multi subj=system_u:system_r:iptables_t:s0 key=(null)

Hash: iptables,iptables_t,denyhosts_var_lock_t,file,write

Is this expected behavior?

No, iptables itself does not contain any code that touches /run/lock/subsys/denyhosts.

There is a Python daemon, that seems to use it: /usr/bin/denyhosts.py from the denyhosts package. 

It seems that denyhosts is passing an open file descriptor to iptables by using os.system calls.

Reassigning to denyhosts.

This is a leak from denyhosts or fail2ban, and should probably just be dontaudited.

Denyhosts (the newer versions) will shell out to iptables.  I have an open ticket for allowing this access but (sadly) I haven't provided the necessary AVCs yet because I'm working on some other part of denyhosts at the moment.  (Reading from the journal, if anyone cares.)

Now, I'd like to fix this properly.  Can anyone give me a hint as to how I'd prevent denyhosts from leaking open FDs to iptables?  Will the current policy even allow denyhosts to shell out to iptables at all?

With using os.open you could also set os.O_CLOEXEC.

With open you have to do it by hand with a fcntl call, that sets FD_CLOEXEC: fcntl.fcntl(fd, fcntl.F_SETFD, fcntl.FD_CLOEXEC)

Or you can use a more secure way than os.system to run processes, like for example something like the runProg code in firewalld.

Thanks for that; I may lift runProg since it's license-compatible, or just use Popen with close_fds=True.

runProg does not do the trick alone - the "Or" above should have been "And".

But Popen with close_fds does the trick.

selinux-policy-3.13.1-105.6.fc21 has been pushed to the Fedora 21 stable repository.  If problems still persist, please make note of it in this bug report.

So what happened here?  The AVCs were marked dontaudit?  If so, that's unfortunate; we should fix bugs in the programs instead of hiding them under more dontaudit rules, as dontaudit rules are simply horrible for discovery and far too often something important is silently denied because of them.

I'm fixing denyhosts so this won't be an issue.  I don't know if any other code is triggering this (fail2ban, maybe) but it should be properly fixed as well.

Guess the problem I've reported originally was fixed (denyhosts can run iptables now and it works - I see drop rules in iptables -L for each host it adds to hosts.deny which doesn't apply for sshd).

Now I get alerts about the leaked file descriptors but for that we can open a new bug, or at least update the title of this one.

OK, so what is state of this issue? SELinux issue is fixed, right? If yes, I suggest close this and open new bug with leaked fd.

I believe this bug is opened correctly. denyhosts needs to fix leaked file descriptors and we can remove dontaudit rules which have been added.

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I'm sorry to post to this relatively "ancient" bug, however, this doesn't seem to have been addressed at all.  For example, there are a number of more recent bugs, e.g. Bug 1259178 .  This behaviour is also observed on a RHEL7.3 system with `denyhosts-2.9-4.el7.noarch`, `selinux-policy-3.13.1-102.el7_3.4.noarch`, and `policycoreutils-2.5-8.el7.x86_64`.

Where would the bugs for packages from EPEL, such as denyhosts, be reported/tracked? Is this bug tracked/relevant to bugzilla.redhat.com? The previous comments here seemed promising, though, it's strange that this is still unresolved years later.

It's unresolved because it's rather bizarre and not something I can personally repeat.

EPEL bugs are tracked in this bugzilla just as Fedora bugs are.

All right, let's see if I can help you reproduce it, then.  The following shows the configuration file for denyhosts.  Can you match that and try to repeat it with an SELinux "targeted" policy in place?

sed -n '/^[a-zA-Z]/p' /etc/denyhosts.conf 
SECURE_LOG = /var/log/secure
HOSTS_DENY = /etc/hosts.deny
PURGE_DENY = 4w
BLOCK_SERVICE  = sshd
DENY_THRESHOLD_INVALID = 4
DENY_THRESHOLD_VALID = 8
DENY_THRESHOLD_ROOT = 1
DENY_THRESHOLD_RESTRICTED = 1
WORK_DIR = /var/lib/denyhosts
ETC_DIR = /etc
SUSPICIOUS_LOGIN_REPORT_ALLOWED_HOSTS=YES
HOSTNAME_LOOKUP=NO
LOCK_FILE = /var/lock/subsys/denyhosts
IPTABLES = /sbin/iptables
ADMIN_EMAIL = root@localhost
SMTP_HOST = localhost
SMTP_PORT = 25
SMTP_FROM = DenyHosts <nobody@localhost>
SMTP_SUBJECT = DenyHosts Report from $[HOSTNAME]
ALLOWED_HOSTS_HOSTNAME_LOOKUP=NO
AGE_RESET_VALID=8d
AGE_RESET_ROOT=35d
AGE_RESET_RESTRICTED=35d
AGE_RESET_INVALID=15d
RESET_ON_SUCCESS = yes
DAEMON_LOG = /var/log/denyhosts
DAEMON_SLEEP = 30s
DAEMON_PURGE = 1h
SYNC_UPLOAD = no
SYNC_DOWNLOAD = yes

Here's an example sealert denial message:


SELinux is preventing /usr/sbin/xtables-multi from write access on the file /run/lock/subsys/denyhosts.

*****  Plugin leaks (86.2 confidence) suggests   *****************************

If you want to ignore xtables-multi trying to write access the denyhosts file, because you believe it should not need this access.
Then you should report this as a bug.  
You can generate a local policy module to dontaudit this access.
Do
# ausearch -x /usr/sbin/xtables-multi --raw | audit2allow -D -M my-iptables
# semodule -i my-iptables.pp

*****  Plugin catchall (14.7 confidence) suggests   **************************

If you believe that xtables-multi should be allowed write access on the denyhosts 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 'iptables' --raw | audit2allow -M my-iptables
# semodule -i my-iptables.pp


Additional Information:
Source Context                system_u:system_r:iptables_t:s0
Target Context                system_u:object_r:denyhosts_var_lock_t:s0
Target Objects                /run/lock/subsys/denyhosts [ file ]
Source                        iptables
Source Path                   /usr/sbin/xtables-multi
Port                          <Unknown>
Host                          hostname
Source RPM Packages           iptables-1.4.21-17.el7.x86_64
Target RPM Packages           
Policy RPM                    selinux-policy-3.13.1-102.el7_3.4.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     hostname
Platform                      Linux hostname 3.10.0-514.el7.x86_64 #1 SMP
                              Wed Oct 19 11:24:13 EDT 2016 x86_64 x86_64
Alert Count                   2
First Seen                    2016-11-03 14:36:00 CDT
Last Seen                     2016-11-03 20:58:46 CDT
Local ID                      a52db65d-1d78-4910-aa97-0de9d3a8744f

Raw Audit Messages
type=AVC msg=audit(1478224726.951:8128): avc:  denied  { write } for  pid=26043 comm="iptables" path="/run/lock/subsys/denyhosts" dev="tmpfs" ino=20416 scontext=system_u:system_r:iptables_t:s0 tcontext=system_u:object_r:denyhosts_var_lock_t:s0 tclass=file


type=AVC msg=audit(1478224726.951:8128): avc:  denied  { append } for  pid=26043 comm="iptables" path="/etc/hosts.deny" dev="dm-1" ino=134438954 scontext=system_u:system_r:iptables_t:s0 tcontext=system_u:object_r:net_conf_t:s0 tclass=file


type=SYSCALL msg=audit(1478224726.951:8128): arch=x86_64 syscall=execve success=yes exit=0 a0=16fc030 a1=16fc110 a2=16fac30 a3=7ffcc5863890 items=2 ppid=1159 pid=26043 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm=iptables exe=/usr/sbin/xtables-multi subj=system_u:system_r:iptables_t:s0 key=(null)

type=CWD msg=audit(1478224726.951:8128): cwd=/

type=PATH msg=audit(1478224726.951:8128): item=0 name=/sbin/iptables inode=201742887 dev=fd:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:iptables_exec_t:s0 objtype=NORMAL

type=PATH msg=audit(1478224726.951:8128): item=1 name=/lib64/ld-linux-x86-64.so.2 inode=201329202 dev=fd:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:ld_so_t:s0 objtype=NORMAL

Hash: iptables,iptables_t,denyhosts_var_lock_t,file,write