[Samba] Samba Wiki: fix to "Configure DHCP to update DNS records" page

[Ing. Claudio Nicora]

I've found another issue that causes the following error (at least with 
my samba-tool 4.7.6):

ERROR(runtime): uncaught exception - (-1073741811, 'An invalid parameter 
was passed to a service or function.')
Jan 27 12:17:11 srv sh[1346]:   File 
"/usr/lib/python2.7/dist-packages/samba/netcmd/__init__.py", line 176, 
in _run
Jan 27 12:17:11 srv sh[1346]:     return self.run(*args, **kwargs)
Jan 27 12:17:11 srv sh[1346]:   File 
"/usr/lib/python2.7/dist-packages/samba/netcmd/dns.py", line 1062, in run
Jan 27 12:17:11 srv sh[1346]:     del_rec_buf)

The error is caused by the script trying to delete an empty IP, and it 
happens when adding a DNS record for a client for the first time.
To reproduce it, delete an (eventually) existing record by running 
dhcpd-dyndns.sh script with "delete" parameter, then reexecute the same 
script with "add".

The line causing the error is this:

------------------------
## update ##
case "${action}" in
     add)
         _KERBEROS
         count=0
         # does host have an existing 'A' record ?
         A_REC=$($SAMBATOOL dns query "${Server}" "${domain}" "${name}" 
A "$KTYPE" 2>/dev/null | grep 'A:' | awk '{print $2}')

         # turn A_REC into an array
         A_REC=("$A_REC")        <---------- ERROR CAUSED BY THIS ASSIGNMENT
------------------------

When "$SAMBATOOL dns query" command returns no record, it returns an 
empty string, so the array conversion becomes like this:
A_REC=("")
which creates an array with 1 element (the empty string) and not an 
empty array ;)

My suggestion is to change array conversion like this:

------------------------
## update ##
case "${action}" in
   add)
     _KERBEROS
     count=0
     # does host have an existing 'A' record ?
     A_REC=$($SAMBATOOL dns query "${Server}" "${domain}" "${name}" A 
"$KTYPE" 2>/dev/null | grep 'A:' | awk '{print $2}')

     # turn A_REC into an array
     if [[ -z "$A_REC" ]]
     then
       A_REC=()
     else
       A_REC=("$A_REC")
     fi
------------------------

Thanks for your work
Claudio


Il 23/01/2023 14:54, Rowland Penny via samba ha scritto:
>
>
> On 23/01/2023 13:47, Ing. Claudio Nicora via samba wrote:
>> @Rowland Penny: thanks for the BASH script to let DHCP update DNS 
>> records 
>> (https://wiki.samba.org/index.php/Configure_DHCP_to_update_DNS_records).
>>
>> I'm suggesting this change:
>> the "if" condition at line 171 does not use the filename assigned to 
>> $keytab variable (at line 41), but a fixed filename (equal to default 
>> $keytab filename).
>> If someone (like me) need to set a different filename, then the 
>> Kerberos keytab test fails.
>>
>> So my suggestion is to replace the "if" condition (around line 171) from
>>
>> ------------------------------
>> # Check for Kerberos keytab
>> if [ ! -f /etc/dhcpduser.keytab ]
>> then
>>    logger "Required keytab $keytab not found, it needs to be created."
>>    ...
>> ------------------------------
>>
>> to
>>
>> ------------------------------
>> # Check for Kerberos keytab
>> if [ ! -f "$keytab" ]
>> then
>>    logger "Required keytab $keytab not found, it needs to be created."
>>    ...
>> ------------------------------
>>
>> Thanks for your work
>
> Thanks for pointing that out, thought I had changed them all, I have 
> now (hopefully)
>
> Rowland
>