Bug 15040 - dwTimestamp not set when updating via dns update
Summary: dwTimestamp not set when updating via dns update
Status: NEW
Alias: None
Product: Samba 4.1 and newer
Classification: Unclassified
Component: DNS plugin (BIND DLZ) (show other bugs)
Version: 4.15.6
Hardware: All All
: P5 normal (vote)
Target Milestone: ---
Assignee: Amitay Isaacs
QA Contact: Samba QA Contact
URL: https://gitlab.com/samba-team/samba/-...
Keywords:
Depends on:
Blocks:
 
Reported: 2022-04-04 11:04 UTC by Michael Saxl
Modified: 2022-06-17 02:19 UTC (History)
0 users

See Also:


Attachments
patch (1.63 KB, patch)
2022-04-04 13:42 UTC, Michael Saxl
no flags Details

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Description Michael Saxl 2022-04-04 11:04:36 UTC
when using nsupdate to add records the new record is added as static record.

as far as I understand this is because in source4/dns_server/dlz_bind9.c b9_parse does not set rec->dwTimeStamp. This results in rec->dwTimeStamp being 0. 0 means "static"

somewhere later there is a call to dns_name_is_static that would suggest that dwTimestamp is set if it is not a static record, but since dns_name_is_static only checks if ONE record has a dwTimeStamp that is 0 (there will always be one if it is a new record, the b9_parse'd one) or it is a SOA record, this will always return true

I think this can be fixed by replacing

if (dns_name_is_static(recs, num_recs)) {
        rec->dwTimeStamp = 0;
} else {
        rec->dwTimeStamp = unix_to_dns_timestamp(time(NULL));
}

with

rec->dwTimeStamp = unix_to_dns_timestamp(time(NULL));
if (dns_name_is_static(recs, num_recs)) {
        rec->dwTimeStamp = 0;
}

if recs is really static there will be a rec that has dwTimeStamp==0 and the new rec->dwTimeStamp will be also set to 0 (=static).
Comment 1 Michael Saxl 2022-04-04 11:51:02 UTC
sorry, the bug report is not precise and I was fooled a bit

the issue can be triggered by:
update add rec.domain.test 300 IN A 1.2.3.4
-> now a dynamic record is added
update delete rec.domain.test
-> now the record is deleted
update add rec.domain.test 300 IN A 1.2.3.4
-> now the record is static

the proposed changes would fix this issue. I am currently not sure why this happens
I think there is a tombstoned entry, but this should be ignored explicitly by dns_name_is_static
Comment 2 Michael Saxl 2022-04-04 13:07:21 UTC
I think I found the issue.

dns_name_is_static(recs, num_recs) is called with the incremented num_recs but the new record is not appended yet. This means the memory is probably not initiallized (talloc_realloc does not zero the memory, else it would probably work since wType would be 0 =DNS_TYPE_TOMBSTONE)
Comment 3 Michael Saxl 2022-04-04 13:42:40 UTC
Created attachment 17262 [details]
patch
Comment 4 Douglas Bagnall 2022-04-21 01:04:58 UTC
The current meege request is https://gitlab.com/samba-team/samba/-/merge_requests/2491 which includes Michael Saxl's patch attached here, along with tests, a related fix for the case where a record is being replaced.
Comment 5 Samba QA Contact 2022-06-17 02:19:11 UTC
This bug was referenced in samba master:

247a39bba046da0a507303a3b58db71ddd10fe0e
9b47d818d04811afac9e4d34b0050c427112fb70
5d89c90ab45bdf0cc2236f71c02b05208fd715f3
937c2cd38a6365924e0eaaa34b60815eced6126c
d0d18934fa0660f85225f6a9387a4583f77bb780
aae689945369cc47574a7cf90faa0e2f20b5b504
590d2e169c4538a41ed1cd99f5cf72f4b6e6e424
f1017c6f2dd136d1654a8ed3734721fc8f3c5b82