[asterisk-bugs] [JIRA] (ASTERISK-20638) SIP dialog matching is incorrect when multiple provisional responses are received with pedantic SIP checking

[Eelco Brolman (JIRA)]

Eelco Brolman created ASTERISK-20638:
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             Summary: SIP dialog matching is incorrect when multiple provisional responses are received with pedantic SIP checking
                 Key: ASTERISK-20638
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-20638
             Project: Asterisk
          Issue Type: Bug
      Security Level: None
          Components: Channels/chan_sip/Interoperability
    Affects Versions: 1.8.17.0
            Reporter: Eelco Brolman


When an external call pickup (INVITE with Replaces: header) is sent to asterisk, asterisk tries to find the call ({{get_sip_pvt_byid_locked}}) based on the {{callid}}, {{fromtag}} and {{totag}} in pedantic mode.

The match will fail in certain situations since the fromtag is not definite (final) as long as only Provisional responses have been received.
When asterisk dials a SIP proxy which does ring group dialing for instance, multiple {{180 Ringing}} responses will be received, and the dialog within asterisk cannot be matched against a single fromtag.

So as long as only provisional responses are received (i.e. when flag {{SIP_PAGE2_DIALOG_ESTABLISHED}} is not set), asterisk should not reject the match based on the fromtag.

The patch for this specific situation is easy of course, you need to test if the dialog is established when checking the fromtag:
{code}
if ((frommismatch && ast_test_flag(&sip_pvt_ptr->flags[1], SIP_PAGE2_DIALOG_ESTABLISHED)) || tomismatch) {
{code}
but I don't know if this breaks other checks.


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