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I encountered a very weird issue, and need expertise on Wireshark internals. First, a few context informations :

  • we use a home compiled version of Wireshark 2.0 where we disable a lot of features such as Qt and GTK3 interface or Lua. Main point is being able to run a recent version of Wireshark (because we developed a plugin infrastructure on top of Wireshark 2 API) on an old distribution based on CentOS 6.5, as well as a more recent one, based on CentOS 7. This "home" version is properly compiled on systems with the right distribution (ie the version we run on CentOS 6.5 is compiled on CentOS 6.5, same with CentOS 7)
  • this "home version" features a patch of the TTE protocol dissector, since we need to use dissectors on top of it, and bundled version doesn't support this feature. So we added a dissector table allowing to add dissectors based on "tte.ctid" field

The problem we observe is a crash when we use a dissector based on this tte.ctid field, but only in CentOS 6.5 context. On CentOS 7, no problem. To exactly pinpoint the problem we used Valgrind, and we don't observe the valgrind error on the CentOS 7 version.

So I guess we did something wrong with the patch, since going through subdissectors overwrites freed memory originally belonging to GDK. My guess is that the problem might be that call_dissector_with_data is called (original TTE dissector code), and then we call dissector_try_uint to call the subdissectors. Is that the way to do it?

Now for the data that will help detect the problem. First, our patch of the TTE dissector :

--- wireshark-2.0.3/epan/dissectors/packet-tte.c    2016-07-19 18:53:17.721839071 +0200
+++ wireshark-2.0.3-patch/epan/dissectors/packet-tte.c  2016-07-20 10:43:25.441521228 +0200
@@ -57,6 +57,8 @@
 static gint ett_tte = -1;
 static gint ett_tte_macdest = -1;

+/* ASL Patch for sub-dissectors */
+static dissector_table_t tte_dissector_table;

 /* Code to actually dissect the packets */
 static int
@@ -68,6 +70,9 @@
     /* Set up structures needed to add the protocol subtree and manage it */
     proto_item *tte_root_item, *tte_macdest_item;
     proto_tree *tte_tree, *tte_macdest_tree;
+    /* ASL Patch for sub-dissectors */
+    guint16 ctid = -1;
+    int ret;

     /* Check that there's enough data */
     if (tvb_reported_length(tvb) < TTE_HEADER_LENGTH)
@@ -96,6 +100,8 @@
         col_set_str(pinfo->cinfo, COL_INFO, "Bogus TTEthernet Frame");
     }

+    
+
     if (tree) {

         /* create display subtree for the protocol */
@@ -120,9 +126,9 @@
         proto_tree_add_item(tte_macdest_tree,
             hf_tte_dst_cf, tvb, 0, TTE_MACDEST_CF_LENGTH, ENC_BIG_ENDIAN);

-        proto_tree_add_item(tte_macdest_tree,
+        proto_tree_add_item_ret_uint(tte_macdest_tree,
             hf_tte_ctid, tvb, TTE_MACDEST_CF_LENGTH,
-            TTE_MACDEST_CTID_LENGTH, ENC_BIG_ENDIAN);
+            TTE_MACDEST_CTID_LENGTH, ENC_BIG_ENDIAN, (guint32*)&ctid);
     }

     /* prevent clearing the Columns...appending cannot be prevented */
@@ -137,7 +143,19 @@
     ethertype_data.fcs_len = 0;

     call_dissector_with_data(ethertype_handle, tvb, pinfo, tree, &ethertype_data);
-    return tvb_reported_length(tvb);
+
+    /* ASL Patch for sub-dissectors */
+    /*    return tvb_reported_length(tvb);*/
+    ret = TTE_HEADER_LENGTH;
+    if (ctid > 0) {
+        int bytes = dissector_try_uint(tte_dissector_table, ctid, tvb, pinfo, tree);
+
+        if (bytes > ret) {
+            ret = bytes;
+        }
+    }
+
+    return ret;
 }

@@ -172,6 +185,9 @@
     proto_register_field_array(proto_tte, hf, array_length(hf));
     proto_register_subtree_array(ett, array_length(ett));

+    /* ASL Patch for sub-dissectors */
+    tte_dissector_table = register_dissector_table("tte.ctid", "CT ID", FT_UINT16, BASE_DEC);
+
     /* Register preferences module */
     tte_module = prefs_register_protocol(proto_tte, NULL);

The valgrind crash trace (only occurring on CentOS 6.5) :

==11024== Invalid write of size 8
==11024==    at 0x65FCA88: dissector_try_heuristic (packet.c:2194)
==11024==    by 0x68BE54A: dissect_eth_common (packet-eth.c:337)
==11024==    by 0x68BF0B8: dissect_eth (packet-eth.c:841)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FE0A5: dissector_try_uint_new (packet.c:1163)
==11024==    by 0x68F03B4: dissect_frame (packet-frame.c:499)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FD400: call_dissector_with_data (packet.c:2563)
==11024==    by 0x65FF495: dissect_record (packet.c:498)
==11024==    by 0x65F20C9: epan_dissect_run (epan.c:332)
==11024==  Address 0x18240000 is 64 bytes inside a block of size 192 free'd
==11024==    at 0x4A063F0: free (vg_replace_malloc.c:446)
==11024==    by 0x3598A10D22: ??? (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598A1580A: ??? (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598A1589A: ??? (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598A0FB0F: cairo_restore (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3597E26F3F: ??? (in /usr/lib64/libgdk-x11-2.0.so.0.2000.1)
==11024==    by 0x3597E2C88F: ??? (in /usr/lib64/libgdk-x11-2.0.so.0.2000.1)
==11024==    by 0x3597E2CF63: ??? (in /usr/lib64/libgdk-x11-2.0.so.0.2000.1)
==11024==    by 0x3597A2887C: pango_renderer_draw_glyphs (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==    by 0x3597A29064: pango_renderer_draw_layout_line (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==    by 0x3597A29364: pango_renderer_draw_layout (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==    by 0x3597E2BB66: gdk_draw_layout_with_colors (in /usr/lib64/libgdk-x11-2.0.so.0.2000.1)
==11024==
==11024== Invalid write of size 8
==11024==    at 0x65FCA90: dissector_try_heuristic (packet.c:2195)
==11024==    by 0x68BE54A: dissect_eth_common (packet-eth.c:337)
==11024==    by 0x68BF0B8: dissect_eth (packet-eth.c:841)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FE0A5: dissector_try_uint_new (packet.c:1163)
==11024==    by 0x68F03B4: dissect_frame (packet-frame.c:499)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FD400: call_dissector_with_data (packet.c:2563)
==11024==    by 0x65FF495: dissect_record (packet.c:498)
==11024==    by 0x65F20C9: epan_dissect_run (epan.c:332)
==11024==  Address 0x18240158 is not stack'd, malloc'd or (recently) free'd
==11024==
==11024== Invalid write of size 2
==11024==    at 0x65FCA9C: dissector_try_heuristic (packet.c:2196)
==11024==    by 0x68BE54A: dissect_eth_common (packet-eth.c:337)
==11024==    by 0x68BF0B8: dissect_eth (packet-eth.c:841)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FE0A5: dissector_try_uint_new (packet.c:1163)
==11024==    by 0x68F03B4: dissect_frame (packet-frame.c:499)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FD400: call_dissector_with_data (packet.c:2563)
==11024==    by 0x65FF495: dissect_record (packet.c:498)
==11024==    by 0x65F20C9: epan_dissect_run (epan.c:332)
==11024==  Address 0x182400c0 is 0 bytes inside a block of size 16 free'd
==11024==    at 0x4A063F0: free (vg_replace_malloc.c:446)
==11024==    by 0x3598A4393A: ??? (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598A2AA5D: ??? (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598A13982: ??? (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598A0E146: cairo_show_glyphs (in /usr/lib64/libcairo.so.2.10800.8)
==11024==    by 0x3598E086D5: ??? (in /usr/lib64/libpangocairo-1.0.so.0.2800.1)
==11024==    by 0x3598E0899A: ??? (in /usr/lib64/libpangocairo-1.0.so.0.2800.1)
==11024==    by 0x3597A2887C: pango_renderer_draw_glyphs (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==    by 0x3598E074DB: ??? (in /usr/lib64/libpangocairo-1.0.so.0.2800.1)
==11024==    by 0x3597A2887C: pango_renderer_draw_glyphs (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==    by 0x3597A29064: pango_renderer_draw_layout_line (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==    by 0x3597A29364: pango_renderer_draw_layout (in /usr/lib64/libpango-1.0.so.0.2800.1)
==11024==
==11024==
==11024== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==11024==  Access not within mapped region at address 0x7FEFF0000
==11024==    at 0x65FCA88: dissector_try_heuristic (packet.c:2194)
==11024==    by 0x68BE54A: dissect_eth_common (packet-eth.c:337)
==11024==    by 0x68BF0B8: dissect_eth (packet-eth.c:841)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FE0A5: dissector_try_uint_new (packet.c:1163)
==11024==    by 0x68F03B4: dissect_frame (packet-frame.c:499)
==11024==    by 0x65FCB6E: call_dissector_through_handle (packet.c:618)
==11024==    by 0x65FD073: call_dissector_work (packet.c:706)
==11024==    by 0x65FD400: call_dissector_with_data (packet.c:2563)
==11024==    by 0x65FF495: dissect_record (packet.c:498)
==11024==    by 0x65F20C9: epan_dissect_run (epan.c:332)
==11024==  If you believe this happened as a result of a stack
==11024==  overflow in your program's main thread (unlikely but
==11024==  possible), you can try to increase the size of the
==11024==  main thread stack using the --main-stacksize= flag.
==11024==  The main thread stack size used in this run was 8388608.

About box information of our CentOS 6.5 Wireshark version :

Version 2.0.7 (Git Rev Unknown from unknown)

Copyright 1998-2016 Gerald Combs <[email protected]> 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 GTK+ 2.20.1, with Cairo 1.8.8, with Pango 1.28.1, with
libpcap, without POSIX capabilities, without libnl, with libz 1.2.3, with GLib
2.26.1, without SMI, without c-ares, without ADNS, without Lua, without GnuTLS,
with Gcrypt 1.4.5, with MIT Kerberos, without GeoIP, without PortAudio, without
AirPcap.

Running on Linux 3.10.47-rt50-RedHawk-6.5.2-trace, with locale en_US.UTF-8, with
libpcap version 1.7.4, with libz 1.2.3, with Gcrypt 1.4.5.
       Intel(R) Xeon(R) CPU E5-2407 0 @ 2.20GHz (with SSE4.2)

Built using gcc 4.4.7 20120313 (Red Hat 4.4.7-4).

About box of our CentOS 7 version, where the problem does not occur :

Version 2.0.7 (Git Rev Unknown from unknown)

Copyright 1998-2016 Gerald Combs <[email protected]> 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 GTK+ 2.24.22, with Cairo 1.12.14, with Pango 1.34.1, with
libpcap, without POSIX capabilities, without libnl, with libz 1.2.7, with GLib
2.36.3, without SMI, without c-ares, without ADNS, without Lua, without GnuTLS,
without Gcrypt, with MIT Kerberos, without GeoIP, without PortAudio, without
AirPcap.

Running on Linux 3.16.7-RedHawk-7.0.2-trace, with locale en_US.UTF-8, with
libpcap version 1.7.4, with libz 1.2.7.
Intel(R) Xeon(R) CPU E5-2637 v3 @ 3.50GHz (with SSE4.2)

Built using gcc 4.8.2 20140120 (Red Hat 4.8.2-16).

Thanks in advance for any help you can provide, because I'm a bit lost here :)

asked 04 Nov '16, 10:04

Florian%20Haradji's gravatar image

Florian Haradji
11115
accept rate: 0%


First of all ctid should be a guint32, not a guint16 (you cannot make assumption on the alignment rules done by the compiler/processor and cast a pointer on guint 16 variable as guint32).

Calling dissector_try_uint after call_dissector_with_data is not an issue by its own, it just means that you give the same payload to 2 different dissectors (so the same data might be dissected twice with different protocols, which is weird).

There are changces your issue is in the dissectors registered to the newly created tte.ctid table. But as you did not share the code, it's up to you to find what's wrong ;)

permanent link

answered 04 Nov '16, 10:29

Pascal%20Quantin's gravatar image

Pascal Quantin
5.5k1060
accept rate: 30%

Well ctid fits on two bytes in the message, but yes, I'll try to use a guint32 instead, and see how it goes.

Yes I need the same data twice, which is weird...I have reasons for that but it will be too long and uninteresting to explain them here :)

I don't think the problem is in the dissectors on top of it, since their exact same code is used on top of the more classic "udp.port" dissector table, and no problem then.

Also, the fact that the problem appears only in CentOS 6.5 where GTK2 and associated libs are in a different version than in CentOS 7, and the valgrind trace explicitly showing gdk/cairo code is quite weird, don't you think?

(04 Nov '16, 10:37) Florian Haradji
1

Well ctid fits on two bytes in the message,

That's completely irrelevant. proto_tree_add_item_ret_uint() is passed a pointer to a guint32, and assumes that the pointer does, in fact, point to a guint32, and thus stores into four bytes starting at the location in the pointer. If you cast a pointer to a guint16 to guint32 *, and pass that to proto_tree_add_item_ret_uint(), proto_tree_add_item_ret_uint() will store into that variable and the two bytes after that variable.

(We didn't complicate the API by having multiple proto_tree_add_item_ret_ routines for different data types, taking return-value arguments of different sizes, so the return value will be bigger than the field for types narrower than FT_UINT32.)

So don't do that. It will cause two random bytes to be overwritten, and where those two bytes happen to be could depend on...

Also, the fact that the problem appears only in CentOS 6.5 where GTK2 and associated libs are in a different version than in CentOS 7

...the version of the compiler used to compile the program, so the behavior could differ between a Wireshark compiled with gcc 4.4.7 20120313 (Red Hat 4.4.7-4) and one compiled with gcc 4.8.2 20140120 (Red Hat 4.8.2-16). That difference could even include one version crashing and another version not crashing.

Valgrind will also complain about the store into the two bytes after the variable; that's what the "Invalid write of size 2" error probably is (unfortunately, Valgrind apparently doesn't handle the way the stack is handled by the call to the dissector, so it's probably not including the dissector itself in the stack trace).

and the valgrind trace explicitly showing gdk/cairo code

It's explicitly showing that one of the invalid writes is to memory that was freed (and presumably allocated) by gdk/cairo code. That's an 8-byte write, so it's probably a completely separate problem from the 2-byte invalid write. It's not immediately obvious what's causing that problem.

(04 Nov '16, 18:00) Guy Harris ♦♦

And...that was it! It was a pretty obvious mistake, but I guess the valgrind stack trace was a little misleading. Plus the fact it didn't crash in another compiler/OS environment...I did not look in the right place.

So thank you all :)

(07 Nov '16, 03:47) Florian Haradji
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question asked: 04 Nov '16, 10:04

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last updated: 07 Nov '16, 03:47

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