[Asterisk-code-review] chan sip: Prevent deadlock when performing BYE with Also tra... (asterisk[11])

[Joshua Colp]

Joshua Colp has uploaded a new patch set (#2).

Change subject: chan_sip: Prevent deadlock when performing BYE with Also transfer.
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chan_sip: Prevent deadlock when performing BYE with Also transfer.

When a BYE with an Also header is successfully processed, and the sender
of the BYE is bridged with another channel, chan_sip will unlock the
owner of the dialog on which the BYE was received, call ast_async_goto()
on the bridged channel, and then re-lock the owner. The reason for this
locking behavior is that ast_async_goto() can result in a masquerade,
which requires that the involved channels are unlocked.

The problem here is that this causes a locking inversion since the
dialog's lock is held when re-locking the owner channel after the async
goto. The lock order is supposed to be channel and then sip_pvt.

The fix proposed is simple. In addition to unlocking the owner channel
before the ast_async_goto() call, also unlock the sip_pvt. Then relock
both after ast_async_goto() returns, being sure to lock the channel and
then the sip_pvt.

ASTERISK-25139 #close
Reported by Gregory Massel

Change-Id: I72c4fc295ec8573bee599e8e9213c5350a3cd224
---
M channels/chan_sip.c
1 file changed, 4 insertions(+), 1 deletion(-)


  git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/44/644/2
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I72c4fc295ec8573bee599e8e9213c5350a3cd224
Gerrit-PatchSet: 2
Gerrit-Project: asterisk
Gerrit-Branch: 11
Gerrit-Owner: Mark Michelson <mmichelson at digium.com>