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f5ethtrailer: Look for trailer after FCS 

Under some conditions the trailer can be added after the FCS has already
been added.  Advance 4 bytes and take a second look for a triler without
needing to resort to walking the trailer.
This commit is contained in:
Jason Cohen 2020-10-06 21:43:21 -05:00 committed by AndersBroman
parent 90cd509d92
commit 888de57c1b
1 changed files with 25 additions and 0 deletions
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25
epan/dissectors/packet-f5ethtrailer.c
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@ -228,6 +228,7 @@ static gint hf_data = -1;
static gint hf_data_str = -1;
static gint hf_dpt_unknown = -1;
static gint hf_trailer_hdr = -1;
static gint hf_orig_fcs = -1;
/* Low */
static gint hf_low_id = -1;
static gint hf_flags = -1;
@ -2853,6 +2854,7 @@ dissect_f5ethtrailer(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *
guint trailer_length;
guint offset = 0;
found_t found = NONE;
gboolean has_fcs = FALSE;
if (tvb_reported_length(tvb) != tvb_captured_length(tvb)) {
/* The trailers are really only helpful if we have the entire trailer. If we
@ -2888,6 +2890,22 @@ dissect_f5ethtrailer(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *
found = NEW_FORMAT;
break;
}
/* It's possible to have the trailer added after the FCS has already been added.
Let's move in 4 bytes and check there. If so, display the Original FCS.
Only add this check for new format trailers. Old format trailers are all but extinct
and likely wouldn't have been added after FCS anyway. The walk trailer prefernce could
find it anyway, and that seems reasonable enough for old format. */
if (tvb_get_ntohl(tvb, offset + 4) == F5_DPT_V1_HDR_MAGIC) {
if (tvb_get_ntohs(tvb, offset + 4 + F5_DPT_V1_HDR_LENGTH_OFF) > trailer_length) {
return 0;
}
found = NEW_FORMAT;
has_fcs = TRUE;
offset += 4;
break;
}
/* Not new format? Are we old format? */
guint tlv_type, tlv_length, tlv_ver;
@ -2924,6 +2942,9 @@ dissect_f5ethtrailer(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *
if (tree) {
trailer_item = proto_tree_add_item(tree, proto_f5ethtrailer, tvb, offset, 0, ENC_NA);
tree = proto_item_add_subtree(trailer_item, ett_f5ethtrailer);
if (has_fcs) {
proto_tree_add_item(tree, hf_orig_fcs, tvb, offset - 4, 4, ENC_NA);
}
}
if (found == NEW_FORMAT) {
@ -3664,6 +3685,10 @@ proto_register_f5ethtrailer(void)
{ "Data", "f5ethtrailer.data.string", FT_STRING, BASE_NONE, NULL,
0x0, NULL, HFILL }
},
{ &hf_orig_fcs,
{ "Original FCS", "f5ethtrailer.orig_fcs", FT_UINT32, BASE_HEX, NULL,
0x0, NULL, HFILL }
},
/* Low parameters */
{ &hf_low_id,