Lua dissector crashes on "string.format("%s", tree.text)"

This issue was migrated from bug 13017 in our old bug tracker.

Original bug information:

Reporter: Redford
Status: RESOLVED FIXED
Product: Wireshark
Component: Dissection engine (libwireshark)
OS: Windows 7
Platform: x86-64
Version: 2.2.1

Redford said:

Build Information: Version 2.2.1 (v2.2.1-0-ga6fbd278 from master-2.2)

Copyright 1998-2016 Gerald Combs <gerald@‍wireshark.org> and contributors. License GPLv2+: GNU GPL version 2 or later <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html> This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled (64-bit) with Qt 5.6.1, with WinPcap (4_1_3), with GLib 2.42.0, with zlib 1.2.8, with SMI 0.4.8, with c-ares 1.12.0, with Lua 5.2.4, with GnuTLS 3.2.15, with Gcrypt 1.6.2, with MIT Kerberos, with GeoIP, with QtMultimedia, with AirPcap.

Running on 64-bit Windows 7 Service Pack 1, build 7601, with locale Polish_Poland.1250, with WinPcap version 4.1.3 (packet.dll version 4.1.0.2980), based on libpcap version 1.0 branch 1_0_rel0b (20091008), with GnuTLS 3.2.15, with Gcrypt 1.6.2, without AirPcap. Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz (with SSE4.2), with 8169MB of physical memory.

Built using Microsoft Visual C++ 12.0 build 40629

It seems that using string.format with contents of TreeItem.text causes a memory access violation.

HOW TO REPRODUCE

1. Add this Lua dissector to Wireshark:
    local proto = Proto("proto", "Protocol")
    function proto.dissector(buffer, pinfo, tree)
        string.format("%s", tree.text)
    end
    local udp_table = DissectorTable.get("udp.port")
    udp_table:add(12345, proto)

2. Start listening on arbitrary interface and send an UDP packet through it, with destination port = 12345.

3. Wireshark will print following message on the console:
01:51:03          Warn Dissector bug, protocol PROTO, in packet 16: STATUS_ACCESS_VIOLATION: dissector accessed an invalid memory address

ADDITIONAL INFO
The crash happens only when "string.format("%s", tree.text)" is present in the code. Additionally, changing "tree.text" to anything else fixes the crash.

added crash libwireshark oswindows version2.2 labels

Jaap Keuter said:

See the very last section (2.11) of README.dissector[1], which states that tree may be NULL and your code has to work either way.

[1] https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob_plain;f=doc/README.dissector

Redford said:

(In reply to Jaap Keuter from comment #1)  
> See the very last section (2.11) of README.dissector[1], which states that  
> tree may be NULL and your code has to work either way.  
>  
> [1]  
> https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob_plain;f=doc/  
> README.dissector  

This README is for writing dissectors in C, not Lua. Even if you would pass `nil` to string.format that doesn't cause a crash in standard Lua interpreter. The bug here seems to break Lua safety - you can't dereference invalid pointer in Lua, this is only possible when there's a bug in its engine or in Wireshark's extensions.

Gerrit Code Review said:

Change 18247 had a related patch set uploaded by Peter Wu: wslua: Do not crash on the root tree item

https://code.wireshark.org/review/18247

Gerrit Code Review said:

Change 18247 merged by Anders Broman: wslua: Do not crash on the root tree item

https://code.wireshark.org/review/18247

closed