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Re: [libvirt] [PATCH RESEND v4 1/2] Introduce Libvirt Wireshark dissector



On 15.01.2014 18:06, Yuto KAWAMURA(kawamuray) wrote:
> From: "Yuto KAWAMURA(kawamuray)" <kawamuray dadada gmail com>
> 
> Introduce Wireshark dissector plugin which adds support to Wireshark
> for dissecting libvirt RPC protocol.
> Added following files to build Wireshark dissector from libvirt source
> tree.
> * tools/wireshark/*: Source tree of Wireshark dissector plugin.
> 
> Added followings to configure.ac or Makefile.am.
> configure.ac
> * --with-wireshark-dissector: Enable support for building Wireshark
>   dissector.
> * --with-ws-plugindir: Specify wireshark plugin directory that dissector
>   will installed.
> * Added tools/wireshark/{Makefile,src/Makefile} to  AC_CONFIG_FILES.
> Makefile.am
> * Added tools/wireshark/ to SUBDIR.
> ---
>  .gitignore                              |    2 +
>  Makefile.am                             |    3 +-
>  cfg.mk                                  |    8 +-
>  configure.ac                            |   72 ++-
>  tools/wireshark/Makefile.am             |   22 +
>  tools/wireshark/README.md               |   31 +
>  tools/wireshark/src/Makefile.am         |   42 ++
>  tools/wireshark/src/packet-libvirt.c    |  512 ++++++++++++++++
>  tools/wireshark/src/packet-libvirt.h    |  128 ++++
>  tools/wireshark/util/genxdrstub.pl      | 1011 +++++++++++++++++++++++++++++++
>  tools/wireshark/util/make-dissector-reg |  198 ++++++
>  11 files changed, 2023 insertions(+), 6 deletions(-)
>  create mode 100644 tools/wireshark/Makefile.am
>  create mode 100644 tools/wireshark/README.md
>  create mode 100644 tools/wireshark/src/Makefile.am
>  create mode 100644 tools/wireshark/src/packet-libvirt.c
>  create mode 100644 tools/wireshark/src/packet-libvirt.h
>  create mode 100755 tools/wireshark/util/genxdrstub.pl
>  create mode 100755 tools/wireshark/util/make-dissector-reg
> 

> diff --git a/tools/wireshark/src/packet-libvirt.c b/tools/wireshark/src/packet-libvirt.c
> new file mode 100644
> index 0000000..2d0350c
> --- /dev/null
> +++ b/tools/wireshark/src/packet-libvirt.c

> +static void
> +dissect_libvirt_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
> +{
> +    goffset offset;
> +    guint32 prog, proc, type, serial, status;
> +    const value_string *vs;
> +
> +    col_set_str(pinfo->cinfo, COL_PROTOCOL, "Libvirt");
> +    col_clear(pinfo->cinfo, COL_INFO);
> +
> +    offset = 4; /* End of length field */
> +    prog   = tvb_get_ntohl(tvb, offset); offset += 4;
> +    offset += 4; /* Ignore version header field */
> +    proc   = tvb_get_ntohl(tvb, offset); offset += 4;
> +    type   = tvb_get_ntohl(tvb, offset); offset += 4;
> +    serial = tvb_get_ntohl(tvb, offset); offset += 4;
> +    status = tvb_get_ntohl(tvb, offset); offset += 4;
> +
> +    col_add_fstr(pinfo->cinfo, COL_INFO, "Prog=%s",
> +                 val_to_str(prog, program_strings, "%x"));
> +
> +    vs = get_program_data(prog, VIR_PROGRAM_PROCSTRINGS);
> +    if (vs == NULL) {
> +        col_append_fstr(pinfo->cinfo, COL_INFO, " Proc=%u", proc);
> +    } else {
> +        col_append_fstr(pinfo->cinfo, COL_INFO, " Proc=%s", val_to_str(proc, vs, "%d"));
> +    }
> +
> +    col_append_fstr(pinfo->cinfo, COL_INFO, " Type=%s Serial=%u Status=%s",
> +                    val_to_str(type, type_strings, "%d"), serial,
> +                    val_to_str(status, status_strings, "%d"));
> +
> +    if (tree) {
> +        gint hf_proc;
> +        proto_item *ti;
> +        proto_tree *libvirt_tree;
> +
> +        ti = proto_tree_add_item(tree, proto_libvirt, tvb, 0, tvb_length(tvb), ENC_NA);
> +        libvirt_tree = proto_item_add_subtree(ti, ett_libvirt);
> +
> +        offset = 0;
> +        proto_tree_add_item(libvirt_tree, hf_libvirt_length,  tvb, offset, 4, ENC_NA); offset += 4;
> +        proto_tree_add_item(libvirt_tree, hf_libvirt_program, tvb, offset, 4, ENC_NA); offset += 4;
> +        proto_tree_add_item(libvirt_tree, hf_libvirt_version, tvb, offset, 4, ENC_NA); offset += 4;
> +
> +        hf_proc = *(int *)get_program_data(prog, VIR_PROGRAM_PROCHFVAR);

There's a possible NULL dereference here. get_program might return NULL in case @prog is not one of REMOTE, QEMU, LXC, KEEPALIVE. This can possibly happen and it did for me indeed:

Program terminated with signal 11, Segmentation fault.
#0  0x00007fac1cc60a86 in dissect_libvirt_message (tvb=0x387acc0, pinfo=0x7fffb9a03100, tree=0x3883090) at packet-libvirt.c:396
396             hf_proc = *(int *)get_program_data(prog, VIR_PROGRAM_PROCHFVAR);
(gdb) bt
#0  0x00007fac1cc60a86 in dissect_libvirt_message (tvb=0x387acc0, pinfo=0x7fffb9a03100, tree=0x3883090) at packet-libvirt.c:396
#1  0x00000034469198fe in tcp_dissect_pdus () from /usr/lib64/libwireshark.so.3
#2  0x00007fac1cc60c0c in dissect_libvirt (tvb=0x3879aa0, pinfo=0x7fffb9a03100, tree=0x3883090) at packet-libvirt.c:424
#3  0x00000034462dff54 in ?? () from /usr/lib64/libwireshark.so.3
#4  0x00000034462e0608 in ?? () from /usr/lib64/libwireshark.so.3
#5  0x00000034462e0e0c in ?? () from /usr/lib64/libwireshark.so.3
#6  0x00000034462e0e67 in dissector_try_uint () from /usr/lib64/libwireshark.so.3
...

(gdb) p /x VIR_PROGRAM_PROCHFVAR
$1 = 0x0
(gdb) p /x prog
$2 = 0xd21c44f9

This happened if I used sasl for authentication (auth_tcp="sasl" listen_tcp=1 listen_tls=0)

> +        if (hf_proc == -1) {
> +            proto_tree_add_none_format(libvirt_tree, -1, tvb, offset, 4, "Unknown proc: %u", proc);
> +        } else {
> +            proto_tree_add_item(libvirt_tree, hf_proc, tvb, offset, 4, ENC_NA);
> +        }
> +        offset += 4;

I've tried to fixed this by applying:
@@ -381,7 +381,7 @@ dissect_libvirt_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
                     val_to_str(status, status_strings, "%d"));
 
     if (tree) {
-        gint hf_proc;
+        gint *hf_proc;
         proto_item *ti;
         proto_tree *libvirt_tree;
 
@@ -393,11 +393,11 @@ dissect_libvirt_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
         proto_tree_add_item(libvirt_tree, hf_libvirt_program, tvb, offset, 4, ENC_NA); offset += 4;
         proto_tree_add_item(libvirt_tree, hf_libvirt_version, tvb, offset, 4, ENC_NA); offset += 4;
 
-        hf_proc = *(int *)get_program_data(prog, VIR_PROGRAM_PROCHFVAR);
-        if (hf_proc == -1) {
+        hf_proc = (int *)get_program_data(prog, VIR_PROGRAM_PROCHFVAR);
+        if (!hf_proc || *hf_proc == -1) {
             proto_tree_add_none_format(libvirt_tree, -1, tvb, offset, 4, "Unknown proc: %u", proc);
         } else {
-            proto_tree_add_item(libvirt_tree, hf_proc, tvb, offset, 4, ENC_NA);
+            proto_tree_add_item(libvirt_tree, *hf_proc, tvb, offset, 4, ENC_NA);
         }
         offset += 4;


but it worked only partially as then I was seeing this error messages (but no segfault :) ):

12:29:09          Warn Dissector bug, protocol libvirt, in packet 32: proto.c:1854: failed assertion "(guint)hfindex < gpa_hfinfo.len" (Unregistered hf!)

The error message kept repeating over and over again. The rest of the patch looks okay. Once you fix this (sending a follow-up patch is just fine) I'll push this. Thanks for taking care of the dissector!

Michal


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