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res_fax: Fix deadlock setting FAXMODE channel variable.

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ASTERISK-25980 added the FAXMODE channel variable to res_fax.c.
Unfortunately, it also introduced a deadlock potential because
set_channel_variables() which sets FAXMODE can be called during a
masquerade.  The ast_channel_get_t38_state() which gets the value used to
set FAXMODE cannot be called with the channel locked.  As a result, local
channels can deadlock because of how they must acquire the locks necessary
to operate.

The intent of FAXMODE is for dialplan to know how a fax was transferred
after the fax completes.  However, the previous patch sets FAXMODE to the
channel's current T.38 state AFTER the fax has completed and where T.38
may have already disconnected.

* Set FAXMODE based upon T.38 negotiations exchanged either with the fax
applications or the fax framehooks.

ASTERISK-26203
Reported by: Etienne Lessard

ASTERISK-24822
Reported by: David Brillert

ASTERISK-22732
Reported by: Richard Mudgett

Change-Id: Id525747254b64c1efe8b1b5973d52ff9719c2ae1
This commit is contained in:
Richard Mudgett
2016-08-23 10:39:01 -05:00
parent 35cf6c7702
commit e8d4f40022
2 changed files with 43 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
include/asterisk/res_fax.h
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@@ -20,16 +20,16 @@
#ifndef _ASTERISK_RES_FAX_H
#define _ASTERISK_RES_FAX_H
#include <asterisk.h>
#include <asterisk/lock.h>
#include <asterisk/linkedlists.h>
#include <asterisk/module.h>
#include <asterisk/utils.h>
#include <asterisk/options.h>
#include <asterisk/frame.h>
#include <asterisk/cli.h>
#include <asterisk/stringfields.h>
#include <asterisk/manager.h>
#include "asterisk.h"
#include "asterisk/lock.h"
#include "asterisk/linkedlists.h"
#include "asterisk/module.h"
#include "asterisk/utils.h"
#include "asterisk/options.h"
#include "asterisk/frame.h"
#include "asterisk/cli.h"
#include "asterisk/stringfields.h"
#include "asterisk/manager.h"
/*! \brief capabilities for res_fax to locate a fax technology module */
enum ast_fax_capabilities {
@@ -187,6 +187,8 @@ struct ast_fax_session_details {
int faxdetect_timeout;
/*! flags used for fax detection */
int faxdetect_flags;
/*! Non-zero if T.38 is negotiated */
int is_t38_negotiated;
};
struct ast_fax_tech;