There is no type_transition rule in the policy that would ensure that /var/lock/ppp gets a correct context when it's created:

# sesearch -T | grep pppd_lock_t
#

If there was such a rule, the /var/lock/ppp directory would be labeled correctly by rpm/yum during the installation of ppp package.

# ls -dZ /var/lock/ppp
ls: cannot access /var/lock/ppp: No such file or directory
# yum -y install ppp
Loaded plugins: product-id, search-disabled-repos, subscription-manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
Resolving Dependencies
--> Running transaction check
---> Package ppp.x86_64 0:2.4.5-33.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package        Arch              Version                 Repository       Size
================================================================================
Installing:
 ppp            x86_64            2.4.5-33.el7            rhel            357 k

Transaction Summary
================================================================================
Install  1 Package

Total download size: 357 k
Installed size: 852 k
Downloading packages:
ppp-2.4.5-33.el7.x86_64.rpm                                | 357 kB   00:00     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : ppp-2.4.5-33.el7.x86_64                                      1/1 
  Verifying  : ppp-2.4.5-33.el7.x86_64                                      1/1 

Installed:
  ppp.x86_64 0:2.4.5-33.el7                                                     

Complete!
# ls -dZ /var/lock/ppp
drwxr-xr-x. root root unconfined_u:object_r:pppd_lock_t:s0 /var/lock/ppp
# 

Following policy module brings such a rule:

# cat mypolicy.te 
policy_module(mypolicy,1.0)

require {
  type rpm_t;
  type rpm_script_t;
  type unconfined_t;
  type var_lock_t;
  type pppd_lock_t;
}

type_transition rpm_t var_lock_t : dir pppd_lock_t "ppp"; 
type_transition rpm_script_t var_lock_t : dir pppd_lock_t "ppp"; 
type_transition unconfined_t var_lock_t : dir pppd_lock_t "ppp"; 
#

Reassigning to selinux-policy per comment 3.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:0763