From our testing it appears that slapd's usage of the crypt function, to check

a user's password on a bind request, is single threaded, rather than being distributed across all of slapds thread. We encountered this problem when bumping the number of hashing rounds for our password hashes from 5,000 to 500,000 as was suggested by our security team.

Is it expected that the hashing of a users password would be bound to one thread?

We ran our tests on a default install of of slapd 2.4.44 on Debian Jessie box with 8 cores.

# Running script with butter user and 10,000,000 rounds of hashing:

$ pidstat -t -p $(pgrep slapd) 5 3 <snip> Average: UID TGID TID %usr %system %guest %CPU CPU Command Average: 108 28458 - 100.00 0.00 0.00 100.00 - slapd Average: 108 - 28458 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 28459 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 28460 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 10679 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 10680 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 17988 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 17993 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 17998 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 18007 22.53 0.00 0.00 22.53 - |__slapd Average: 108 - 19109 16.80 0.00 0.00 16.80 - |__slapd Average: 108 - 19110 0.07 0.00 0.00 0.07 - |__slapd Average: 108 - 19111 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 19112 60.73 0.00 0.00 60.73 - |__slapd Average: 108 - 19113 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 27438 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 27439 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 27440 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 27441 0.00 0.00 0.00 0.00 - |__slapd

# Running script with bubbles user and 5,000 rounds of hashing:

$ pidstat -t -p $(pgrep slapd) 5 3 <snip> Average: UID TGID TID %usr %system %guest %CPU CPU Command Average: 108 28458 - 109.59 0.87 0.00 110.46 - slapd Average: 108 - 28458 0.00 0.00 0.00 0.00 - |__slapd Average: 108 - 28459 0.80 2.80 0.00 3.60 - |__slapd Average: 108 - 28460 8.79 0.07 0.00 8.86 - |__slapd Average: 108 - 10679 7.00 0.07 0.00 7.06 - |__slapd Average: 108 - 10680 8.19 0.07 0.00 8.26 - |__slapd Average: 108 - 17988 3.80 0.07 0.00 3.86 - |__slapd Average: 108 - 17993 3.73 0.00 0.00 3.73 - |__slapd Average: 108 - 17998 7.46 0.00 0.00 7.46 - |__slapd Average: 108 - 18007 7.66 0.00 0.00 7.66 - |__slapd Average: 108 - 19109 8.93 0.07 0.00 8.99 - |__slapd Average: 108 - 19110 4.73 0.07 0.00 4.80 - |__slapd Average: 108 - 19111 9.33 0.00 0.00 9.33 - |__slapd Average: 108 - 19112 9.26 0.13 0.00 9.39 - |__slapd Average: 108 - 19113 2.40 0.00 0.00 2.40 - |__slapd Average: 108 - 27438 8.13 0.07 0.00 8.19 - |__slapd Average: 108 - 27439 1.87 0.07 0.00 1.93 - |__slapd Average: 108 - 27440 7.79 0.00 0.00 7.79 - |__slapd Average: 108 - 27441 7.00 0.00 0.00 7.00 - |__slapd

# Test ldif:

$ cat example.ldif dn: o=example o: example objectclass: organization

dn: ou=people, o=example ou: people objectclass: organizationalunit

dn: ou=groups, o=example ou: groups objectclass: organizationalunit

dn: cn=butter, ou=people, o=example objectclass: inetOrgPerson cn: butter sn: butter # {CRYPT}$6$rounds=10000000$ykk4zGD3ODNR$iMP/zYeisoWTYgxLtPv1qzoo/dVrYQLAb9sKlRMBgPTfFrr9lTzEEkJ9NcFdGI/MiRxHSx/1x3rnw3RkNRMer/ # 'everyone loves butter' userPassword:: e0NSWVBUfSQ2JHJvdW5kcz0xMDAwMDAwMCR5a2s0ekdEM09ETlIkaU1QL3pZZWlzb1dUWWd4THRQdjFxem9vL2RWcllRTEFiOXNLbFJNQmdQVGZGcnI5bFR6RUVrSjlOY0ZkR0kvTWlSeEhTeC8xeDNybnczUmtOUk1lci8= uid: butter

dn: cn=bubbles, ou=people, o=example objectclass: inetOrgPerson cn: bubbles sn: bubbles # {CRYPT}$6$rounds=5000$vY9dl4.rTyasVXCH$nlSXEZFnMn31NThCBWmfDy8EhaaZz6amUI8iukO8dpAnxMUaKK/78FqMVSi5iRbMvwkS6RNYhh4WhNzxDe.8r0 # 'everyone loves bubbles' userPassword:: e0NSWVBUfSQ2JHJvdW5kcz01MDAwJHZZOWRsNC5yVHlhc1ZYQ0gkbmxTWEVaRm5NbjMxTlRoQ0JXbWZEeThFaGFhWno2YW1VSThpdWtPOGRwQW54TVVhS0svNzhGcU1WU2k1aVJiTXZ3a1M2Uk5ZaGg0V2hOenhEZS44cjA= uid: bubbles

dn: cn=admin,o=example objectClass: simpleSecurityObject objectClass: organizationalRole cn: admin description: LDAP administrator userPassword:: e1NTSEF9SmFDaTRvZkRqQ2F3RHR2VVJQZWdleFoxZHFWNWRENUo= structuralObjectClass: organizationalRole

# Test script:

$ cat whoamis #!/bin/bash

USER=$1

trap cleanup SIGINT

cleanup() { kill -9 $(jobs -p) exit 1 }

while true; do if [[ $(jobs | wc -l) -lt 8 ]]; then ldapwhoami -x -D cn=${USER},ou=people,o=example -H ldap://localhost -w "everyone loves ${USER}" >/dev/null & else wait -n fi done