Description of problem:

 vrrp_script broken from v1.3.0 when we try to verify local port with "</dev/tcp/127.0.0.1/22"

Version-Release number of selected component (if applicable):
Starting keepalived v1.3.0


How reproducible:
We can reproduce with a normal keepalived setup with a vrrp_script to check a local port "22" using the below syntax.

vrrp_script chk_sshd {
       script "</dev/tcp/127.0.0.1/22"
}



Steps to Reproduce:
1. Configure keepalived with vrrp_script as shown above.
2. start keepalived, vrrp_script fails.
3.

Actual results: Vrrp_script fails and gets disabled.


Expected results: vrrp_script should succeed.


Additional info:
Keepalived configuration
========================
[root@keepalived-master keepalived]# cat keepalived.conf
! Configuration File for keepalived
vrrp_script chk_sshd {
       script "</dev/tcp/127.0.0.1/22"
}

vrrp_instance VI_1 {

    state MASTER
    interface ens12
    virtual_router_id 80
    smtp_alert
    priority 110
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 056282
    }
    virtual_ipaddress {
        192.168.101.200/24 dev ens12
    }
    track_script {
     chk_sshd
    }
}



Logs showing failure
=====================
Jan 15 12:19:34 keepalived-master systemd[1]: Stopping LVS and VRRP High Availability Monitor...
Jan 15 12:19:34 keepalived-master Keepalived_vrrp[3672]: VRRP_Instance(VI_1) sent 0 priority
Jan 15 12:19:34 keepalived-master Keepalived_vrrp[3672]: VRRP_Instance(VI_1) removing protocol VIPs.
Jan 15 12:19:35 keepalived-master systemd[1]: Starting LVS and VRRP High Availability Monitor...
Jan 15 12:19:35 keepalived-master systemd[1]: PID file /var/run/keepalived.pid not readable (yet?) after start.
Jan 15 12:19:35 keepalived-master Keepalived[3699]: Starting Healthcheck child process, pid=3700
Jan 15 12:19:35 keepalived-master Keepalived[3699]: Starting VRRP child process, pid=3701
Jan 15 12:19:35 keepalived-master systemd[1]: Started LVS and VRRP High Availability Monitor.
Jan 15 12:19:35 keepalived-master Keepalived_healthcheckers[3700]: Initializing ipvs
Jan 15 12:19:35 keepalived-master Keepalived_healthcheckers[3700]: Opening file '/etc/keepalived/keepalived.conf'.
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: Registering Kernel netlink reflector
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: Registering Kernel netlink command channel
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: Registering gratuitous ARP shared channel
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: Opening file '/etc/keepalived/keepalived.conf'.
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: WARNING - default user 'keepalived_script' for script execution does not exist - please create.
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: Unable to access script ``</dev/tcp/127.0.0.1/22``
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: Disabling track script chk_sshd since not found
Jan 15 12:19:35 keepalived-master Keepalived_vrrp[3701]: VRRP_Instance(VI_1) removing protocol VIPs.

NOTE :    If we use 'bash -c /dev/tcp/127.0.0.1/22' it works with v1.3.0 as well. However the documentation refers to the above syntax. 

     It seems to be fixed upstream, please refer below.

https://github.com/acassen/keepalived/commit/5cd5fff78de11178c51ca245ff5de61a86b85049

     Its easily reproducible locally with the above configuration.