-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Evan Huus
Sent: den 11 oktober 2012 22:54
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] RFD: Limiting scope of ep_ memory
On Thu, Oct 11, 2012 at 4:41 PM, Jakub Zawadzki <darkjames-ws@xxxxxxxxxxxx> wrote:
>> Hi,
>>
>> Right now ep_ memory is freed at the begining of epan_dissect_run(),
>> which means that pointers allocated by ep_ can be safety accessed only
>> before dissecting next packet.
>>
>> When using GUI epan_dissect_run() can be run when refreshing interface (think: packet list).
>> Which can happen at *any* time. Originally it caused bug #5284.
>>
>> Right now we (I and Evan) can't reproduce this bug, but there's still the problem.
>>
>>
>> To make it reproductable (and clear) I want to make ep_ memory
>> available
>> *only* when dissecting packet, i.e.
>>
>> epan_dissect_run():
>> ep_free_all();
>> dissect_packet(edt, pseudo_header, data, fd, cinfo);
>> ep_free_all();
>>
>> Taps also use ep_ memory, so I propose new function:
>>
>> epan_dissect_run_tap():
>> ep_free_all();
>> tap_queue_init(edt);
>> dissect_packet(edt, pseudo_header, data, fd, cinfo);
>> tap_push_tapped_queue(edt);
>> ep_free_all();
>>
>> (For now I want to have ep_free_all() before and after dissecting,
>> before release we can remove the one before).
>>
>> Thanks to it, and memory scrubbing, any ep_ allocated pointer used
>> after dissecting should be catched fast.
>>
>> It'll be no longer possible to save ep_ pointers in taps [1], or
>> communicate with UI by storing ep_ memory in packet_info.
>>
>>
>> I hope this proposal is understable and sane.
>> If we want to allow using ep_ memory between epan_dissect_init() and
>> epan_dissect_cleanup() we need more complicated allocator, which we currently don't have.
>> It's doable, but I'm not sure if really needed.
>>
>> Regards,
>> Jakub.
>>
>> [1] http://www.wireshark.org/lists/wireshark-dev/201210/msg00094.html
+1
>I also think we should limit it so it's not possible to use ep_ memory while there isn't a packet being
>dissected. During my original attempt to create a safer allocator I was forced to add a dummy memory pool to>
>work around the numerous locations that use ep_ memory when there isn't a packet in scope. If there isn't a
>packet currently in scope we have no guarantees when ep_ memory will next be freed, and so it isn't safe to be >used.
>
>Perhaps the
>> ep_free_all();
>> dissect_packet(edt, pseudo_header, data, fd, cinfo);
>> ep_free_all();
in Jakub's patch could be
>> ep_start_packet();
>> dissect_packet(edt, pseudo_header, data, fd, cinfo);
>> ep_end_packet();
>where the two new functions just call ep_free_all() and flip a boolean. If ep_alloc() is called when the
>boolean is false (there is no packet in scope) then it should g_warning (or assert, but I figure trunk would be >unusable for days if we do that).
>
>Other thoughts?
>Evan
Why not make a patch that developers can try out and start debugging?
Regards
Anders
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