Wireshark · Wireshark-dev: Re: [Wireshark-dev] 1.12.0rc2 : tshark crash when message is on 3 packets

[Graham Bloice <graham.bloice@xxxxxxxxxxxxx>]

On 18 June 2014 13:12, wsgd <wsgd@xxxxxxx> wrote:

Le 18/06/2014 00:41, Pascal Quantin a écrit :

2014-06-18 0:11 GMT+02:00 Pascal Quantin <pascal.quantin@xxxxxxxxx>:

2014-06-16 22:44 GMT+02:00 wsgd <wsgd@xxxxxxx>:

Hello,

My protocol (only to test this problem) specifications :
tcp port 20640
message is 5 bytes long



command line : tshark -r pb.cap  -T text -V
--> crash (see pb.1.12.0.txt)
**
ERROR:print.c:838:get_field_data: code should not be reached

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.



wireshark does not crash and display is ok
tshark 1.10.6 does not crash and display is ok (see pb.1.10.6.txt)


Plugin dissector code is into packet-tcp-5-bytes.c



Regards,
Olivier

Hi Olivier,

thanks for the report.
This is a regression introduced by g21e0a63b2 commit for bug 9169. I proposed a fix (not calling the data dissector when a subdissector claims that the current TCP fragment needs more desegmentation) here: https://code.wireshark.org/review/2350

Regards,
Pascal.

Hi Olivier,

as Evan noted in the review of my patch, the data dissector should not even be called as your dissector accepted the packet. It appears that there is a small bug in your current code. In function dissect_tcp_5_bytes(), replacing the line 30:
            return  offset;

by
            return  offset + available;

does not trigger the crash.

With the previous code, your dissector was returning the value 0 for frame 4, like if the packet was rejected. But at the same time you were considering the packet as acceptable and changing the pinfo->desegment_len, leading to an inconsistent state that should have been caught by a missing check in packet-tcp.c

Regards,
Pascal.

Hi Pascal,


Ok, my fault.
Sorry for the inconvenience.



Question : the dissect function must return void or int ?
I know both versions exist.
Is there one deprecated or one better ?



Only void dissect function into http://www.wireshark.org/docs/wsdg_html_chunked/ChDissectAdd.html.

void dissect function into https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob_plain;f=doc/README.dissector :

static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)

I can't see it in the docs anywhere (which is an omission that should be corrected), but epan\packet.h holds a little information about the types of dissector functions.  New code should be using the new dissector type.

Graham