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



2014/1/16 Michal Privoznik <mprivozn redhat com>:
> 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
>

Thanks for review Michal.
Fix patch for this bug is following.
Regoards.

diff --git a/tools/wireshark/src/packet-libvirt.c
b/tools/wireshark/src/packet-libvirt.c
index 2d0350c..d64ecce 100644
--- a/tools/wireshark/src/packet-libvirt.c
+++ b/tools/wireshark/src/packet-libvirt.c
@@ -39,6 +39,7 @@ static int proto_libvirt = -1;
 static int hf_libvirt_length = -1;
 static int hf_libvirt_program = -1;
 static int hf_libvirt_version = -1;
+static int hf_libvirt_procedure = -1;
 static int hf_libvirt_type = -1;
 static int hf_libvirt_serial = -1;
 static int hf_libvirt_status = -1;
@@ -381,7 +382,7 @@ 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 +394,12 @@ 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) {
-            proto_tree_add_none_format(libvirt_tree, -1, tvb, offset,
4, "Unknown proc: %u", proc);
+        hf_proc = (int *)get_program_data(prog, VIR_PROGRAM_PROCHFVAR);
+        if (hf_proc != NULL && *hf_proc != -1) {
+            proto_tree_add_item(libvirt_tree, *hf_proc, tvb, offset,
4, ENC_NA);
         } else {
-            proto_tree_add_item(libvirt_tree, hf_proc, tvb, offset, 4, ENC_NA);
+            /* No string representation, but still useful displaying
proc number */
+            proto_tree_add_item(libvirt_tree, hf_libvirt_procedure,
tvb, offset, 4, ENC_NA);
         }
         offset += 4;

@@ -446,6 +448,12 @@ proto_register_libvirt(void)
             NULL, 0x0,
             NULL, HFILL}
         },
+        { &hf_libvirt_procedure,
+          { "procedure", "libvirt.procedure",
+            FT_INT32, BASE_DEC,
+            NULL, 0x0,
+            NULL, HFILL}
+        },
         { &hf_libvirt_type,
           { "type", "libvirt.type",
             FT_INT32, BASE_DEC,

kawamuray


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