[asterisk-dev] [Code Review] Delay the destruction of an ast_filestream structure until the frame embedded within is freed.

[Mark Michelson]

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Review request for Asterisk Developers.


Summary
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This patch is to alleviate a memory corruption problem observed on a production system. Valgrind showed that there were invalid accesses to frames in the function ast_frame_free. It appears that the problem had to do with the fact that the frames were allocated as part of an ast_filestream structure. After the ast_filestream is freed, we still attempt to operate on the frame that was part of it.

This patch solves the problem by marking frames which are part of an ast_filestream structure with a flag, AST_FRFLAG_FROM_FILESTREAM. If ast_filestream_close is called on a filestream whose frame is still flagged, then we will delay the destruction of the ast_filestream until ast_frfree is called on the frame.

I'm confident that this patch is correct, especially since similar measures have been taken with frames embedded in ast_dsp structures and ast_trans_pvt structures. The main concern I have is that I needed to repurpose a field in the ast_filestream structure to be used as a means of indicating that the ast_filestream had been requested to be destroyed. I chose the 'lastwriteformat' field for this and set it to -1 in the case that ast_filestream_close is called prior to the AST_FRFLAG_FROM_FILESTREAM being cleared from the embedded frame. It is important that we are sure that the lastwriteformat variable has no other legitimate reason to be set to -1. Grepping the source shows that the only time this variable is used is in the function ast_writestream. It gets set to the subclass of a voice frame if the frame's format is not one for which we have set up a translator. All voice frame subclasses are non-negative to the best of my knowledge.


Diffs
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  branches/1.4/channels/chan_sip.c 152927 
  branches/1.4/include/asterisk/file.h 152927 
  branches/1.4/include/asterisk/frame.h 152927 
  branches/1.4/main/file.c 152927 
  branches/1.4/main/frame.c 152927 

Diff: http://reviewboard.digium.com/r/46/diff


Testing
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I have done some simple file playbacks just to be sure that there is no horrible breakage.


Thanks,

Mark