Re: Someone please help me on this Reassemly fragmentation

[Pascal Quantin <pascal.quantin () gmail com>]

Le 25 févr. 2015 10:07, "Raj sekar" <mrajsekar () gmail com> a écrit :
> i have a off-line capture file..
>
> iam developing dissector for customised protocol
>
> i have a old ethereal tool for the same protocol now iam developing in
wireshark.
> My message pdu got 3 different message types
>
>   1. Beginning of message
>   2. continuation of message
>   3. end of message
>
> in one Frame at a time it can receive any one of this message
>
> when it End of message sequence comes i need to reassemble whole PDU
>
> i have opened in ethereal tool and my output are like this
>
> Frame Number
> Message type
> pollflag
> NS (sequence Number)
> NR (SEquence ID)
>
>
> 283
> Beginning of message
> 0
> 0
> 0
> 343
> End of message
> 0
> 1
> 0
>  -> Reassembly done here
>
>
> 379
> Beginning of message
> 0
> 2
> 1
> 414
> Continuation of message
> 0
> 3
> 1
> 416
> Continuation of message
> 0
> 4
> 1
> 417
> End of Message
> 1
> 5
> 1
>  -> Reassembly done here
>
>
> 536
> Beginning of message
> 0
> 6
> 2
> 541
> End of meassage
> 0
> 7
> 2
>  -> Reassembly done here

Hi,

I'm really happy to see that you did not follow the explanations and
advices I gave you yesterday by private email because you contacted me
directly instead of sending to the mailing list.
As I told you your code cannot work as-is because it assumes that you will
always get a begin - continuation - end sequence (so 3 fragments). If this
is not the case and if you are sure to always receive the fragments in
order, you could use an (evil ;)) global variable to keep track of the
current fragment number. See a suggestion below in your code. If you put
some effort in understanding what I explained you, and ensure that you are
correctly setting the parameters of the reassembly API, it should work
correctly.


> I have used my code structure like this
>
>
> guint32 rem_length;
> guint8 iflag,pf,stype,flag_sel,num_sel,i,sflag;  //
> guint32 pdu_len;
> guint8 save_fragmented;
> gboolean more_frags = FALSE;
> gboolean need_frag = FALSE;
> const *data = NULL;
> //tvbuff_t *try_tvb = NULL;
> //proto_item *frag_tree_item;
> tvbuff_t  *rass_tvb = NULL;
> tvbuff_t  *mns_tvb = NULL;
> guint32 msg_seqid;

replace it by:

static guint32 msg_seqid = 0;

> guint32 mns_seqid = 0;
> guint32 mns_seqnum = 0;
> fragment_head *frag_msg = NULL;
> gboolean reassembled = FALSE;
> //guint32  reassembled_in = 0;
> tvbuff_t * res_tvb = NULL;
> fragment_head * frag_head = NULL;
> proto_tree *ptree = NULL;
> ptree = proto_tree_get_parent(tree);
>
>
>          pf = (tvb_get_guint8(next_tvb, offset_payload) & 0x40) >>6 ; //
Bit 7 pf
>          mns_seqnum = (tvb_get_ntohs(next_tvb, offset_payload) &
0x3ff00000) >>20; // 10 Bits are ns
>          offset_payload +=1;
>          mns_seqid = (tvb_get_ntohs(next_tvb, offset_payload) &
0x0ffc0000) >>18; // 10 bits are nr
>          offset_payload +=1;
>          stype = (tvb_get_guint8(next_tvb, offset_payload) & 0x03) ; // 2
bits LSB are Stype
>          offset_payload -=2;
>
>          FT_BCnPDU_item = proto_tree_add_text(tree, next_tvb,
offset_payload, bctsdu_length, "BCnPDU (Formatted) : Information, I flag =
0x%02x, Pf = 0x%02x, Ns = 0x%02x, Nr = 0x%02x ",
iflag,pf,mns_seqnum,mns_seqid );
>          FT_BCnPDU_tree = proto_item_add_subtree(FT_BCnPDU_item,
ett_FT_BCnPDU);
>          proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, 1,
" bctsdu_length: %d", bctsdu_length);
>          proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, 1,
"I flag : 0x%02x (%s)", iflag,val_to_str(iflag,true_false_vals,"%s"));
>          proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, 1,
"Pf : 0x%02x (%d)", pf,pf);
>          proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, 2,
"Ns : 0x%02x (%d)", mns_seqnum,mns_seqnum);
>          offset_payload +=1;
>          bctsdu_length-=1;
>          proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, 2,
"Nr : 0x%02x (%d)", mns_seqid,mns_seqid);
>          offset_payload +=1;
>          bctsdu_length-=1;
>          proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, 1,
"BCnSegType : 0x%02x (%s)", stype,val_to_str(stype,BCn_Seg_Type_vals,"%s"));
>          offset_payload +=1;
>          bctsdu_length-=1;
>
>
>          switch (stype){
>
>          case 0x00: // Continuation of Message
>
>            msg_seqid=1;

replace it by:

msg_seqid++;

>            bctsdu_length+=1;
>
>            rem_length = bctsdu_length;
>            proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload,
rem_length , "PDU data : %d", rem_length);
>          break;
>
>          case 0x01: // Beginning of Message
>
>             msg_seqid=0;
>
>
>             BCnPDU_stype_item = proto_tree_add_text(FT_BCnPDU_tree,
next_tvb, offset_payload, 1, "%s",val_to_str(stype,BCn_Seg_Type_vals,"%s"));
>             BCnPDU_stype_tree = proto_item_add_subtree(BCnPDU_stype_item,
ett_BCnPDU_stype);
>             BCnPDU_bom_item = proto_tree_add_text(BCnPDU_stype_tree,
next_tvb, offset_payload, 1, "MACSAPFLAGS");
>             BCnPDU_bom_tree = proto_item_add_subtree(BCnPDU_bom_item,
ett_BCnPDU_bom);
>             temp_val = (tvb_get_guint8(next_tvb, offset_payload) & 0x80)
> > 7 ; // Bit 8 - Flow Control
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, 1, "Flow Control : 0x%02x (%s)",
temp_val,val_to_str(temp_val, true_false_vals,"%s"));
>             temp_val = (tvb_get_guint8(next_tvb, offset_payload) & 0x40)
> > 6 ; // Bit 7 - Reserved l
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, 1, "Reserved l : 0x%02x (%d)", temp_val,temp_val);
>             temp_val = (tvb_get_guint8(next_tvb, offset_payload) & 0x20)
> > 5 ; // Bit 6 - Expedited
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, 1, "Expedited : 0x%02x (%s)", temp_val,val_to_str(temp_val,
true_false_vals,"%s"));
>             temp_val = (tvb_get_guint8(next_tvb, offset_payload) & 0x10)
> > 4 ; // Bit 5 - OAM PDU Flag
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, 1, "OAM PDU Flag : 0x%02x (%s)",
temp_val,val_to_str(temp_val, true_false_vals,"%s"));
>             temp_val = (tvb_get_guint8(next_tvb, offset_payload) & 0x08)
> > 3 ; // Bit 4 - Reserved 2
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, 1, "Reserved 2 : 0x%02x (%d)", temp_val,temp_val);
>             pdu_len = (tvb_get_ntohl(next_tvb, offset_payload) &
0x07ff0000) >>16; // PDU Length - 11 Bits
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, 2, "PDU Length : 0x%02x (%d)", pdu_len,pdu_len);
>             offset_payload+=2;
>             bctsdu_length-=2;
>
>
>             if (rem_length >= pdu_len){
>
>             rem_length-=2;
>
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, rem_length, "PDU data (if) : %d ", rem_length);
>             } else {
>
>             proto_tree_add_text(BCnPDU_bom_tree, next_tvb,
offset_payload, rem_length, "PDU data (else) : %d ", rem_length);
>             }
>
>
>          break;
>
>          case 0x02: // End of Message
>
>            msg_seqid=2;

replace it by:

msg_seqid++;

>            bctsdu_length+=2;
>
>            more_frags=TRUE;
>
>
>            rem_length =  bctsdu_length;
>            rem_length-=2;
>
>            proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload,
rem_length , "PDU data : %d", rem_length);
>            disable_CRC=1;
>
>
>          break;
>
>          case 0x03: // Single Segment Message
>             // No need of fragmentation and reassembly
>             offset_payload+=1;
>             bctsdu_length-=1;
>             if (bctsdu_length>0){
>
>              ALSIGPDU(next_tvb, pinfo, tree);
>                }
>
>
>            break;
>
>            }
>
>             if ( stype==0x01 || stype==0x02 || stype==0x00  ){
>
>
>                        pinfo->fragmented = TRUE;
>                        save_fragmented = pinfo->fragmented;
>
>                        frag_head =
fragment_add_check(&mns_reassembly_table,
>                           next_tvb,
>                           offset_payload,
>                           pinfo,
>                           msg_seqid,

this should be mns_seqid

>                           NULL,
>                           mns_seqid,

this should be msg_seqid

>                           pdu_length,
>                           ((msg_seqid == 2)?0:1));

this should be:

(stype == 0x02) ? FALSE : TRUE)

>                         if (frag_head != NULL) {
>
>                            col_append_str(pinfo->cinfo, COL_INFO, "
[Fragment Successful]");
>                           } else {
>
>                           col_append_str(pinfo->cinfo, COL_INFO, "
[Fragment Not Successful]");
>                           }
>
>                           save_fragmented = pinfo->fragmented;
>                        pinfo->fragmented = FALSE;
>
>
>
>                        res_tvb = process_reassembled_data( next_tvb,
offset_payload, pinfo, "Reassembled PDU", frag_head, &mns_frag_items, NULL,
FT_BCnPDU_tree );
>                        save_fragmented = pinfo->fragmented;
>                        pinfo->fragmented = FALSE;
>
>                        if (res_tvb) {
>
>                           col_append_str(pinfo->cinfo, COL_INFO, " [mns
reassembled]");
>                           } else {
>                             col_append_str(pinfo->cinfo, COL_INFO, "[mns
not reassembled ]");
>                             }
>                          offset_payload+=rem_length;
>                          bctsdu_length-=rem_length;
>
>                    }
>
>
>
>     I dont have any clue my fragmentation always not succesful. please
help.
> Thanks
>
> Best Regards
> Raj
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