git: 3651c4f42285 - stable/12 - tcp: fix cwnd restricted SACK retransmission loop

The branch stable/12 has been updated by rscheff:

URL: https://cgit.FreeBSD.org/src/commit/?id=3651c4f42285644938e2f5bc924ab8c7ed857f83

commit 3651c4f42285644938e2f5bc924ab8c7ed857f83
Author:     Richard Scheffenegger <rscheff@FreeBSD.org>
AuthorDate: 2022-09-22 10:55:25 +0000
Commit:     Richard Scheffenegger <rscheff@FreeBSD.org>
CommitDate: 2022-09-25 08:52:56 +0000

    tcp: fix cwnd restricted SACK retransmission loop
    
    While doing the initial SACK retransmission segment while heavily cwnd
    constrained, tcp_ouput can erroneously send out the entire sendbuffer
    again. This may happen after an retransmission timeout, which resets
    snd_nxt to snd_una while the SACK scoreboard is still populated.
    
    Reviewed By:            tuexen, #transport
    PR:                     264257
    PR:                     263445
    PR:                     260393
    MFC after:              3 days
    Sponsored by:           NetApp, Inc.
    Differential Revision:  https://reviews.freebsd.org/D36637
    
    (cherry picked from commit a743fc8826fa348b09d219632594c537f8e5690e)
---
 sys/netinet/tcp_output.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index e8d585a15d1c..125227991a51 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -394,7 +394,7 @@ after_sack_rexmit:
 		else {
 			int32_t cwin;
 
-                        /*
+			/*
 			 * We are inside of a SACK recovery episode and are
 			 * sending new data, having retransmitted all the
 			 * data possible in the scoreboard.
@@ -410,8 +410,8 @@ after_sack_rexmit:
 			 * of len is bungled by the optimizer.
 			 */
 			if (len > 0) {
-				cwin = tp->snd_cwnd - 
-					(tp->snd_nxt - tp->sack_newdata) -
+				cwin = tp->snd_cwnd - imax(0, (int32_t)
+					(tp->snd_nxt - tp->sack_newdata)) -
 					sack_bytes_rxmt;
 				if (cwin < 0)
 					cwin = 0;