Description of problem:

When /etc/security/limits.conf or /etc/security/limits.d/*.conf contain many entries, sudo is very slow, "sudo -i" even slower:

# time sudo -i true

real	0m4.645s
user	0m4.594s
sys	0m0.046s


# time sudo true

real	0m1.350s
user	0m1.276s
sys	0m0.075s


Version-Release number of selected component (if applicable):

sudo-1.8.23-3.el7.x86_64


How reproducible:

Always


Steps to Reproduce:
1. Create 40 "groups" entries containing 13 lines (hence 520 lines in total)

# cat > ~/template.per_group << EOF
ENTRY        -       fsize           unlimited
ENTRY        -       core            unlimited
ENTRY        -       data            unlimited
ENTRY        -       memlock         unlimited
ENTRY        -       nofile          100000
ENTRY        -       rss             unlimited
ENTRY        -       stack           unlimited
ENTRY        -       cpu             unlimited
ENTRY        -       nproc           unlimited
ENTRY        -       as              unlimited
ENTRY        -       maxlogins       unlimited
ENTRY        -       locks           unlimited
ENTRY        -       sigpending      unlimited
EOF

# for i in $(seq 1 40); do group="@mygroup$i"; sed "s/ENTRY/$group/g" ~/template.per_group > /etc/security/limits.d/group$i.conf; done

2. Run "sudo -i" or "sudo"

# time sudo -i true


Actual results:

real	0m4.826s
user	0m4.780s
sys	0m0.041s


Expected results:

real	0m0.340s
user	0m0.292s
sys	0m0.042s


Additional info:

This is due to sudo executing multiple times "pam_limits.so" (3 times for "sudo -i", 2 times for "sudo") due to having "pam_limits.so" defined in multiple places:
- /etc/pam.d/sudo-i

  session    required     pam_limits.so
  session    include      sudo

- /etc/pam.d/sudo

  session    required     pam_limits.so
  session    include      system-auth

- /etc/pam.d/system-auth

  session     required      pam_limits.so

Removing the "session    required     pam_limits.so" from /etc/pam.d/sudo-i and /etc/pam.d/sudo fixes the issue.