Jason

On Wed, Apr 11, 2012 at 2:22 PM, Daniel-Constantin Mierla <miconda@gmail.com> wrote:

Hello,

the internal dialog id - the pair h_entry,h_id - seems exposed to some issues. They:
- h_entry is the slot index (in the internal hash table) where the dialog structure will be stored
- h_id is an incremented counter for each slot

h_entry is computed as a hash function over Call-Id value, then made modulo nr. of slots.

The problems can appear upon restart when changing the hash_size module parameter:

http://kamailio.org/docs/modules/stable/modules_k/dialog.html#id2534423

If it is decremented, then some dialogs might be left outside since their h_entry might not be valid anymore. Also, when hash_size is changed, for matching on SIP dialog attributes of ongoing calls, the hash function over callid made modulo over the new nr. of slots may get a different hash table slot index, resulting in dialog structure not being found.

A very unlikely issue is caused by the h_id, which being incremented can overflow and start from 0 again. But will overlap if an dialog is still going on after 2^32 new dialogs on that hash table slot were initiated.

I wanted to brought all in the discussion to make a decision. I see few options for the moment:
1) document this issue, so a restart with change of hash_size parameter must have 0 active dialogs
2) replace h_entry with the value of the hash function over call id, doing modulo operation each time to find the slot. The unlikely issue with overflow of h_id is still there
3) switch over another kind of unique id (sriud.{c,h} added recently in lib/srutils/ can be an option). This will imply changing the database structure

Besides these, might be better to drop using the Record-Route header parameter to carry dialog id and just do SIP based dialog matching. Completely trusting those tokens in RR parameter might add some security risks and if there is a fallback to SIP-based dialog matching, using the shortcut with RR does not impact anymore that much.

Opinions and other suggestions?

Cheers,
Daniel

--
Daniel-Constantin Mierla
Kamailio Advanced Training, April 23-26, 2012, Berlin, Germany
http://www.asipto.com/index.php/kamailio-advanced-training/

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