dcb25bb057
Channel masquerading had a conflict with autochannel locking. When locking autochannel->channel, the channel is fetched from the autochannel and then locked. During the fetch, the autochannel -- which has no locks itself -- can be modified by someone who owns the channel lock. That means that the value of autochan->channel cannot be trusted until you hold the lock. In practice, this caused problems with Local channels getting masqueraded away while the ChanSpy attempted to get info from that channel. The old channel which was about to get removed got locked, but the new (replaced) channel got unlocked (no-op). Because the replaced channel was now locked (and would never get unlocked), it couldn't get removed from the channel list in a timely manner, and would now cause deadlocks when iterating over the channel list. This change checks the autochannel after locking the channel for changes to the autochannel. If the channel had been changed, the lock is reobtained on the new channel. In theory it seems possible that after this fix, the lock attempt on the old (wrong) channel can be on an already destroyed lock, maybe causing a crash. But that hasn't been observed in the wild and is harder induce than the current deadlock. Thanks go to Filip Frank for suggesting a fix similar to this and especially to IRC user hexanol for pointing out why this deadlock was possible and testing this fix. And to Richard for catching my rookie while loop mistake ;) ASTERISK-25321 #close Change-Id: I293ae0014e531cd0e675c3f02d1d118a98683def
99 lines
2.6 KiB
C
99 lines
2.6 KiB
C
/*
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* Asterisk -- An open source telephony toolkit.
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*
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* Copyright (C) 2009, Digium, Inc.
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*
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* Mark Michelson <mmichelson@digium.com>
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*
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* See http://www.asterisk.org for more information about
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* the Asterisk project. Please do not directly contact
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* any of the maintainers of this project for assistance;
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* the project provides a web site, mailing lists and IRC
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* channels for your use.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License Version 2. See the LICENSE file
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* at the top of the source tree.
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*/
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/*!
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* \file
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* \brief "smart" channels
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*
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* \author Mark Michelson <mmichelson@digium.com>
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*/
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/*** MODULEINFO
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<support_level>core</support_level>
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***/
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#include "asterisk.h"
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ASTERISK_REGISTER_FILE()
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#include "asterisk/autochan.h"
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#include "asterisk/utils.h"
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#include "asterisk/linkedlists.h"
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#include "asterisk/options.h"
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#include "asterisk/channel.h"
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struct ast_autochan *ast_autochan_setup(struct ast_channel *chan)
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{
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struct ast_autochan *autochan;
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if (!chan) {
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return NULL;
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}
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if (!(autochan = ast_calloc(1, sizeof(*autochan)))) {
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return NULL;
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}
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autochan->chan = ast_channel_ref(chan);
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ast_channel_lock(autochan->chan); /* autochan is still private, no need for ast_autochan_channel_lock() */
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AST_LIST_INSERT_TAIL(ast_channel_autochans(autochan->chan), autochan, list);
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ast_channel_unlock(autochan->chan);
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ast_debug(1, "Created autochan %p to hold channel %s (%p)\n", autochan, ast_channel_name(chan), chan);
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return autochan;
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}
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void ast_autochan_destroy(struct ast_autochan *autochan)
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{
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struct ast_autochan *autochan_iter;
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ast_autochan_channel_lock(autochan);
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AST_LIST_TRAVERSE_SAFE_BEGIN(ast_channel_autochans(autochan->chan), autochan_iter, list) {
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if (autochan_iter == autochan) {
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AST_LIST_REMOVE_CURRENT(list);
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ast_debug(1, "Removed autochan %p from the list, about to free it\n", autochan);
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break;
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}
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}
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AST_LIST_TRAVERSE_SAFE_END;
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ast_autochan_channel_unlock(autochan);
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autochan->chan = ast_channel_unref(autochan->chan);
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ast_free(autochan);
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}
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void ast_autochan_new_channel(struct ast_channel *old_chan, struct ast_channel *new_chan)
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{
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struct ast_autochan *autochan;
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AST_LIST_APPEND_LIST(ast_channel_autochans(new_chan), ast_channel_autochans(old_chan), list);
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AST_LIST_TRAVERSE(ast_channel_autochans(new_chan), autochan, list) {
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if (autochan->chan == old_chan) {
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autochan->chan = ast_channel_unref(old_chan);
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autochan->chan = ast_channel_ref(new_chan);
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ast_debug(1, "Autochan %p used to hold channel %s (%p) but now holds channel %s (%p)\n",
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autochan, ast_channel_name(old_chan), old_chan, ast_channel_name(new_chan), new_chan);
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}
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}
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}
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