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Reassembly: make streaming reassembly support DESEGMENT_ONE_MORE_SEGMENT 

Make reassemble_streaming_data_and_call_subdissector() allow subdissector
to set pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT.
This commit is contained in:
Huang Qiangxiong 2023-06-07 00:32:03 +08:00 committed by Pascal Quantin
parent 7839a96040
commit aa54f33700
2 changed files with 50 additions and 20 deletions
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63
epan/reassemble.c
View File

@ -3274,6 +3274,7 @@ reassemble_streaming_data_and_call_subdissector(
guint32 reassembly_id = 0, frag_offset = 0;
fragment_head* head = NULL;
gboolean need_more = FALSE;
gboolean found_BoMSP = FALSE;
multisegment_pdu_t* cur_msp = NULL, * prev_msp = NULL;
guint16 save_can_desegment;
int save_desegment_offset;
@ -3287,7 +3288,11 @@ reassemble_streaming_data_and_call_subdissector(
/* calculate how many bytes of this payload belongs to previous MSP (EoMSP) */
if (!PINFO_FD_VISITED(pinfo)) {
/* this is first scan */
if (reassembly_info->prev_deseg_len > 0) {
if (reassembly_info->prev_deseg_len == DESEGMENT_ONE_MORE_SEGMENT) {
/* assuming the entire tvb belongs to the previous MSP */
bytes_belong_to_prev_msp = length;
reassembly_info->prev_deseg_len = length;
} else if (reassembly_info->prev_deseg_len > 0) {
/* part or all of current payload belong to previous MSP */
bytes_belong_to_prev_msp = MIN(reassembly_info->prev_deseg_len, length);
reassembly_info->prev_deseg_len -= bytes_belong_to_prev_msp;
@ -3382,25 +3387,43 @@ reassemble_streaming_data_and_call_subdissector(
/* that must only happen during first scan the reassembly_info->prev_deseg_len might be only the
* head length of entire message. */
DISSECTOR_ASSERT(!PINFO_FD_VISITED(pinfo));
DISSECTOR_ASSERT_HINT(pinfo->desegment_len != DESEGMENT_ONE_MORE_SEGMENT
&& pinfo->desegment_len != DESEGMENT_UNTIL_FIN, "Subdissector MUST NOT "
"set pinfo->desegment_len to DESEGMENT_ONE_MORE_SEGMENT or DESEGMENT_UNTIL_FIN. "
"Instead, it can set pinfo->desegment_len to the length of head if the length of "
"entire message is not able to be determined.");
DISSECTOR_ASSERT_HINT(pinfo->desegment_offset == 0, "Subdissector MUST NOT set pinfo->desegment_len greater than "
"the length of one message if the length message is undetermined.");
DISSECTOR_ASSERT_HINT(pinfo->desegment_len != DESEGMENT_UNTIL_FIN, "Subdissector MUST NOT "
"set pinfo->desegment_len to DESEGMENT_UNTIL_FIN. Instead, it can set pinfo->desegment_len to "
" DESEGMENT_ONE_MORE_SEGMENT or the length of head if the length of entire message is not able to be determined.");
/* Remove the data added by previous fragment_add(), and reopen fragments for adding more bytes. */
fragment_truncate(&streaming_reassembly_table, pinfo, reassembly_id, NULL, reassembly_info->last_msp->length);
fragment_set_partial_reassembly(&streaming_reassembly_table, pinfo, reassembly_id, NULL);
if (pinfo->desegment_offset > 0) {
DISSECTOR_ASSERT_HINT(pinfo->desegment_offset > reassembly_info->last_msp->length
&& pinfo->desegment_offset < reassembly_info->last_msp->length + bytes_belong_to_prev_msp,
wmem_strdup_printf(pinfo->pool,
"Subdissector MUST NOT set pinfo->desegment_offset(%d) in previous or next part of MSP, must between (%d, %d).",
pinfo->desegment_offset, reassembly_info->last_msp->length, reassembly_info->last_msp->length + bytes_belong_to_prev_msp));
reassembly_info->prev_deseg_len = bytes_belong_to_prev_msp + pinfo->desegment_len;
bytes_belong_to_prev_msp = MIN(reassembly_info->prev_deseg_len, length);
reassembly_info->prev_deseg_len -= bytes_belong_to_prev_msp;
need_more = (reassembly_info->prev_deseg_len > 0);
} else {
/* shorten the bytes_belong_to_prev_msp and just truncate the ressembled tvb */
bytes_belong_to_prev_msp = pinfo->desegment_offset - reassembly_info->last_msp->length;
fragment_truncate(&streaming_reassembly_table, pinfo, reassembly_id, NULL, pinfo->desegment_offset);
found_BoMSP = TRUE;
} else {
if (pinfo->desegment_len == DESEGMENT_ONE_MORE_SEGMENT) {
/* just need more bytes, all remaining bytes belongs to previous MSP (to run fragment_add again) */
bytes_belong_to_prev_msp = length;
}
/* Remove the data added by previous fragment_add(), and reopen fragments for adding more bytes. */
fragment_truncate(&streaming_reassembly_table, pinfo, reassembly_id, NULL, reassembly_info->last_msp->length);
fragment_set_partial_reassembly(&streaming_reassembly_table, pinfo, reassembly_id, NULL);
reassembly_info->prev_deseg_len = bytes_belong_to_prev_msp + pinfo->desegment_len;
bytes_belong_to_prev_msp = MIN(reassembly_info->prev_deseg_len, length);
reassembly_info->prev_deseg_len -= bytes_belong_to_prev_msp;
need_more = (reassembly_info->prev_deseg_len > 0);
continue;
}
}
if (pinfo->desegment_len == 0 || found_BoMSP) {
/* We will arrive here, only when the MSP is defragmented and dissected or this
* payload all belongs to previous MSP (only fragment_add() with need_more=TRUE called)
* or BoMSP is parsed while pinfo->desegment_offset > 0 and pinfo->desegment_len != 0
*/
offset += bytes_belong_to_prev_msp;
length -= bytes_belong_to_prev_msp;
@ -3413,14 +3436,14 @@ reassemble_streaming_data_and_call_subdissector(
/* completed current msp */
reassembly_info->last_msp->last_frame = cur_frame_num;
reassembly_info->last_msp->end_offset_at_last_frame = offset;
reassembly_info->prev_deseg_len = 0;
reassembly_info->prev_deseg_len = pinfo->desegment_len;
}
bytes_belong_to_prev_msp = 0; /* break */
}
}
/* to find and handle OmNFP, and find BoMSP at first scan. */
if (length > 0) {
if (length > 0 && !found_BoMSP) {
if (!PINFO_FD_VISITED(pinfo)) {
/* It is first scan, to dissect remaining bytes to find whether it is OmNFP only, or BoMSP only or OmNFP + BoMSP. */
datalen = length;
@ -3448,6 +3471,9 @@ reassemble_streaming_data_and_call_subdissector(
pinfo, subdissector_tree, subdissector_data);
if (pinfo->desegment_len) {
DISSECTOR_ASSERT_HINT(pinfo->desegment_len != DESEGMENT_UNTIL_FIN, "Subdissector MUST NOT "
"set pinfo->desegment_len to DESEGMENT_UNTIL_FIN. Instead, it can set pinfo->desegment_len to "
" DESEGMENT_ONE_MORE_SEGMENT or the length of head if the length of entire message is not able to be determined.");
/* only happen during first scan */
DISSECTOR_ASSERT(!PINFO_FD_VISITED(pinfo) && datalen == length);
offset += pinfo->desegment_offset;
@ -3471,6 +3497,7 @@ reassemble_streaming_data_and_call_subdissector(
/* create a msp for current frame during first scan */
cur_msp = wmem_new0(wmem_file_scope(), multisegment_pdu_t);
cur_msp->first_frame = cur_frame_num;
cur_msp->last_frame = G_MAXUINT64;
cur_msp->start_offset_at_first_frame = offset;
cur_msp->length = length;
cur_msp->streaming_reassembly_id = reassembly_id = create_streaming_reassembly_id();

7
epan/reassemble.h
View File

@ -809,13 +809,15 @@ streaming_reassembly_info_new(void);
*
* The subdissector (ProtoB dissector) needs to set the pinfo->desegment_len to cooperate with the function
* reassemble_streaming_data_and_call_subdissector() to complete the reassembly task.
* The pinfo->desegment_len should contain the estimated number of additional bytes required for completing
* The pinfo->desegment_len should be DESEGMENT_ONE_MORE_SEGMENT or contain the estimated number of additional bytes required for completing
* the current PDU (MSP), and set pinfo->desegment_offset to the offset in the tvbuff at which the dissector will
* continue processing when next called. Next time the subdissector is called, it will be passed a tvbuff composed
* of the end of the data from the previous tvbuff together with desegment_len more bytes. If the dissector cannot
* tell how many more bytes it will need, it should set pinfo->desegment_len to additional bytes required for parsing
* message head. It will then be called again as soon as more data becomes available. Subdissector MUST NOT set the
* pinfo->desegment_len to DESEGMENT_ONE_MORE_SEGMENT or DESEGMENT_UNTIL_FIN, we don't support these two values yet.
* pinfo->desegment_len to DESEGMENT_UNTIL_FIN, we don't support it yet. Note that the subdissector MUST return the
* length of the tvb handled by itself (return 0 length if nothing is parsed in MoMSP), otherwise it may cause
* unexpected dissecting errors.
*
* Following is sample code of ProtoB which on top of ProtoA mentioned above:
* <code>
@ -832,6 +834,7 @@ streaming_reassembly_info_new(void);
* if (pinfo->can_desegment) {
* pinfo->desegment_offset = offset;
* // calculate how many additional bytes needed to parse head of a ProtoB message
* // or just return DESEGMENT_ONE_MORE_SEGMENT
* pinfo->desegment_len = PROTO_B_MESSAGE_HEAD_LEN - (tvb_len - offset);
* return offset; // return the length handled by ProtoB
* }