SSSD's AD objectSID to Linux UID mapping algorithm, implemented in Python

sid_to_uid.py

#!/bin/python3

import sys


SSS_IDMAP_DEFAULT_LOWER = 200000
SSS_IDMAP_DEFAULT_UPPER = 2000200000
SSS_IDMAP_DEFAULT_RANGESIZE = 200000

def murmur3_32(data, seed = 0):
    c1 = 0xcc9e2d51
    c2 = 0x1b873593

    length = len(data)
    h1 = seed
    roundedEnd = (length & 0xfffffffc)  # round down to 4 byte block
    for i in range(0, roundedEnd, 4):
      # little endian load order
      k1 = (ord(data[i]) & 0xff) | ((ord(data[i + 1]) & 0xff) << 8) | \
           ((ord(data[i + 2]) & 0xff) << 16) | (ord(data[i + 3]) << 24)
      k1 *= c1
      k1 = (k1 << 15) | ((k1 & 0xffffffff) >> 17) # ROTL32(k1,15)
      k1 *= c2

      h1 ^= k1
      h1 = (h1 << 13) | ((h1 & 0xffffffff) >> 19)  # ROTL32(h1,13)
      h1 = h1 * 5 + 0xe6546b64

    # tail
    k1 = 0

    val = length & 0x03
    if val == 3:
        k1 = (ord(data[roundedEnd + 2]) & 0xff) << 16
    # fallthrough
    if val in [2, 3]:
        k1 |= (ord(data[roundedEnd + 1]) & 0xff) << 8
    # fallthrough
    if val in [1, 2, 3]:
        k1 |= ord(data[roundedEnd]) & 0xff
        k1 *= c1
        k1 = (k1 << 15) | ((k1 & 0xffffffff) >> 17)  # ROTL32(k1,15)
        k1 *= c2
        h1 ^= k1

    # finalization
    h1 ^= length

    # fmix(h1)
    h1 ^= ((h1 & 0xffffffff) >> 16)
    h1 *= 0x85ebca6b
    h1 ^= ((h1 & 0xffffffff) >> 13)
    h1 *= 0xc2b2ae35
    h1 ^= ((h1 & 0xffffffff) >> 16)

    return h1 & 0xffffffff

def main():
    if(len(sys.argv) != 2):
        print('Usage: '+sys.argv[0]+' <SID>')
        print('You can find your user SID by reading the objectSid attribute via LDAP query.')
        sys.exit(1)
    if(len(sys.argv[1].rsplit('-')) != 8):
        print('This is not a valid SID!')
        sys.exit(1)

    domain_sid = sys.argv[1].rsplit('-', 1)[0]
    rid = int(sys.argv[1].rsplit('-', 1)[1])

    # see: https://manpages.ubuntu.com/manpages/bionic/en/man5/sssd-ad.5.html#id%20mapping
    slices = (SSS_IDMAP_DEFAULT_UPPER - SSS_IDMAP_DEFAULT_LOWER) / SSS_IDMAP_DEFAULT_RANGESIZE
    domain_sid_hash = murmur3_32(domain_sid, 0xdeadbeef)
    slice = int( ((domain_sid_hash % slices) * SSS_IDMAP_DEFAULT_RANGESIZE) + SSS_IDMAP_DEFAULT_LOWER )
    uid = slice + rid
    print(uid)

if(__name__ == '__main__'):
    main()