Description of problem:
SELinux is preventing master from using the 'dac_read_search' capabilities.

*****  Plugin dac_override (91.4 confidence) suggests   **********************

If you want to help identify if domain needs this access or you have a file with the wrong permissions on your system
Then turn on full auditing to get path information about the offending file and generate the error again.
Do

Turn on full auditing
# auditctl -w /etc/shadow -p w
Try to recreate AVC. Then execute
# ausearch -m avc -ts recent
If you see PATH record check ownership/permissions on file, and fix it,
otherwise report as a bugzilla.

*****  Plugin catchall (9.59 confidence) suggests   **************************

If you believe that master should have the dac_read_search capability 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 'master' --raw | audit2allow -M my-master
# semodule -X 300 -i my-master.pp

Additional Information:
Source Context                system_u:system_r:postfix_master_t:s0
Target Context                system_u:system_r:postfix_master_t:s0
Target Objects                Unknown [ capability ]
Source                        master
Source Path                   master
Port                          <Unknown>
Host                          (removed)
Source RPM Packages           
Target RPM Packages           
Policy RPM                    <Unknown>
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     (removed)
Platform                      Linux (removed) 4.12.4-300.fc26.x86_64 #1 SMP Thu
                              Jul 27 23:09:13 UTC 2017 x86_64 x86_64
Alert Count                   9
First Seen                    2017-07-28 17:35:50 BST
Last Seen                     2017-07-28 17:41:50 BST
Local ID                      1cb37858-5b8e-47c2-a99e-27897826b553

Raw Audit Messages
type=AVC msg=audit(1501260110.205:1660): avc:  denied  { dac_read_search } for  pid=1018 comm="master" capability=2  scontext=system_u:system_r:postfix_master_t:s0 tcontext=system_u:system_r:postfix_master_t:s0 tclass=capability permissive=0


Hash: master,postfix_master_t,postfix_master_t,capability,dac_read_search


Additional info:
component:      selinux-policy
reporter:       libreport-2.9.1
hashmarkername: setroubleshoot
kernel:         4.12.4-300.fc26.x86_64
type:           libreport