git: 17cc6689eb16 - stable/13 - MFC 9febbc454190: Fix for natd(8) sending wrong sequence number after TCP retransmission, terminating a TCP connection.
Hans Petter Selasky
hselasky at FreeBSD.org
Wed Mar 3 09:49:05 UTC 2021
The branch stable/13 has been updated by hselasky:
URL: https://cgit.FreeBSD.org/src/commit/?id=17cc6689eb16302f897023c1b227c30de1e373a4
commit 17cc6689eb16302f897023c1b227c30de1e373a4
Author: Hans Petter Selasky <hselasky at FreeBSD.org>
AuthorDate: 2021-02-22 10:58:46 +0000
Commit: Hans Petter Selasky <hselasky at FreeBSD.org>
CommitDate: 2021-03-03 09:47:44 +0000
MFC 9febbc454190:
Fix for natd(8) sending wrong sequence number after TCP retransmission,
terminating a TCP connection.
If a TCP packet must be retransmitted and the data length has changed in the
retransmitted packet, due to the internal workings of TCP, typically when ACK
packets are lost, then there is a 30% chance that the logic in GetDeltaSeqOut()
will find the correct length, which is the last length received.
This can be explained as follows:
If a "227 Entering Passive Mode" packet must be retransmittet and the length
changes from 51 to 50 bytes, for example, then we have three cases for the
list scan in GetDeltaSeqOut(), depending on how many prior packets were
received modulus N_LINK_TCP_DATA=3:
case 1: index 0: original packet 51
index 1: retransmitted packet 50
index 2: not relevant
case 2: index 0: not relevant
index 1: original packet 51
index 2: retransmitted packet 50
case 3: index 0: retransmitted packet 50
index 1: not relevant
index 2: original packet 51
This patch simply changes the searching order for TCP packets, always starting
at the last received packet instead of any received packet, in
GetDeltaAckIn() and GetDeltaSeqOut().
Else no functional changes.
Discussed with: rscheff@
Submitted by: Andreas Longwitz <longwitz at incore.de>
PR: 230755
Sponsored by: Mellanox Technologies // NVIDIA Networking
(cherry picked from commit 9febbc4541903bb8e6b0f1c84988c98b2f7c96ef)
---
sys/netinet/libalias/alias_db.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/sys/netinet/libalias/alias_db.c b/sys/netinet/libalias/alias_db.c
index 1f85a606b2d5..c87273c863ca 100644
--- a/sys/netinet/libalias/alias_db.c
+++ b/sys/netinet/libalias/alias_db.c
@@ -1937,14 +1937,18 @@ TCP packet. To do this, a circular list of ACK numbers where the TCP
packet size was altered is searched.
*/
- int i;
+ int i, j;
int delta, ack_diff_min;
delta = 0;
ack_diff_min = -1;
- for (i = 0; i < N_LINK_TCP_DATA; i++) {
+ i = lnk->data.tcp->state.index;
+ for (j = 0; j < N_LINK_TCP_DATA; j++) {
struct ack_data_record x;
+ if (i == 0)
+ i = N_LINK_TCP_DATA;
+ i--;
x = lnk->data.tcp->ack[i];
if (x.active == 1) {
int ack_diff;
@@ -1976,14 +1980,18 @@ TCP packet. To do this, a circular list of ACK numbers where the TCP
packet size was altered is searched.
*/
- int i;
+ int i, j;
int delta, seq_diff_min;
delta = 0;
seq_diff_min = -1;
- for (i = 0; i < N_LINK_TCP_DATA; i++) {
+ i = lnk->data.tcp->state.index;
+ for (j = 0; j < N_LINK_TCP_DATA; j++) {
struct ack_data_record x;
+ if (i == 0)
+ i = N_LINK_TCP_DATA;
+ i--;
x = lnk->data.tcp->ack[i];
if (x.active == 1) {
int seq_diff;
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