Patch "tcp: Update window clamping condition" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tcp: Update window clamping condition

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-update-window-clamping-condition.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 87ed2007bb3e2e4f71ef2f27713d1b2bad8bc521
Author: Subash Abhinov Kasiviswanathan <quic_subashab@xxxxxxxxxxx>
Date:   Thu Aug 8 16:06:40 2024 -0700

    tcp: Update window clamping condition
    
    [ Upstream commit a2cbb1603943281a604f5adc48079a148db5cb0d ]
    
    This patch is based on the discussions between Neal Cardwell and
    Eric Dumazet in the link
    https://lore.kernel.org/netdev/20240726204105.1466841-1-quic_subashab@xxxxxxxxxxx/
    
    It was correctly pointed out that tp->window_clamp would not be
    updated in cases where net.ipv4.tcp_moderate_rcvbuf=0 or if
    (copied <= tp->rcvq_space.space). While it is expected for most
    setups to leave the sysctl enabled, the latter condition may
    not end up hitting depending on the TCP receive queue size and
    the pattern of arriving data.
    
    The updated check should be hit only on initial MSS update from
    TCP_MIN_MSS to measured MSS value and subsequently if there was
    an update to a larger value.
    
    Fixes: 05f76b2d634e ("tcp: Adjust clamping window for applications specifying SO_RCVBUF")
    Signed-off-by: Sean Tranchetti <quic_stranche@xxxxxxxxxxx>
    Signed-off-by: Subash Abhinov Kasiviswanathan <quic_subashab@xxxxxxxxxxx>
    Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d0364cff65c9f..24c7c955dc955 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -243,9 +243,14 @@ static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 		 */
 		if (unlikely(len != icsk->icsk_ack.rcv_mss)) {
 			u64 val = (u64)skb->len << TCP_RMEM_TO_WIN_SCALE;
+			u8 old_ratio = tcp_sk(sk)->scaling_ratio;
 
 			do_div(val, skb->truesize);
 			tcp_sk(sk)->scaling_ratio = val ? val : 1;
+
+			if (old_ratio != tcp_sk(sk)->scaling_ratio)
+				WRITE_ONCE(tcp_sk(sk)->window_clamp,
+					   tcp_win_from_space(sk, sk->sk_rcvbuf));
 		}
 		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
 					       tcp_sk(sk)->advmss);
@@ -748,7 +753,8 @@ void tcp_rcv_space_adjust(struct sock *sk)
 	 * <prev RTT . ><current RTT .. ><next RTT .... >
 	 */
 
-	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)) {
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
+	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 		u64 rcvwin, grow;
 		int rcvbuf;
 
@@ -764,22 +770,12 @@ void tcp_rcv_space_adjust(struct sock *sk)
 
 		rcvbuf = min_t(u64, tcp_space_from_win(sk, rcvwin),
 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
-		if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
-			if (rcvbuf > sk->sk_rcvbuf) {
-				WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
-
-				/* Make the window clamp follow along.  */
-				WRITE_ONCE(tp->window_clamp,
-					   tcp_win_from_space(sk, rcvbuf));
-			}
-		} else {
-			/* Make the window clamp follow along while being bounded
-			 * by SO_RCVBUF.
-			 */
-			int clamp = tcp_win_from_space(sk, min(rcvbuf, sk->sk_rcvbuf));
+		if (rcvbuf > sk->sk_rcvbuf) {
+			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
 
-			if (clamp > tp->window_clamp)
-				WRITE_ONCE(tp->window_clamp, clamp);
+			/* Make the window clamp follow along.  */
+			WRITE_ONCE(tp->window_clamp,
+				   tcp_win_from_space(sk, rcvbuf));
 		}
 	}
 	tp->rcvq_space.space = copied;