Patch "tcp: Adjust clamping window for applications specifying SO_RCVBUF" has been added to the 6.10-stable tree

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

    tcp: Adjust clamping window for applications specifying SO_RCVBUF

to the 6.10-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-adjust-clamping-window-for-applications-specifyi.patch
and it can be found in the queue-6.10 subdirectory.

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



commit 5eb845ea86956a3c670dd86e0a30f79e90dd6b56
Author: Subash Abhinov Kasiviswanathan <quic_subashab@xxxxxxxxxxx>
Date:   Fri Jul 26 13:41:05 2024 -0700

    tcp: Adjust clamping window for applications specifying SO_RCVBUF
    
    [ Upstream commit 05f76b2d634e65ab34472802d9b142ea9e03f74e ]
    
    tp->scaling_ratio is not updated based on skb->len/skb->truesize once
    SO_RCVBUF is set leading to the maximum window scaling to be 25% of
    rcvbuf after
    commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale")
    and 50% of rcvbuf after
    commit 697a6c8cec03 ("tcp: increase the default TCP scaling ratio").
    50% tries to emulate the behavior of older kernels using
    sysctl_tcp_adv_win_scale with default value.
    
    Systems which were using a different values of sysctl_tcp_adv_win_scale
    in older kernels ended up seeing reduced download speeds in certain
    cases as covered in https://lists.openwall.net/netdev/2024/05/15/13
    While the sysctl scheme is no longer acceptable, the value of 50% is
    a bit conservative when the skb->len/skb->truesize ratio is later
    determined to be ~0.66.
    
    Applications not specifying SO_RCVBUF update the window scaling and
    the receiver buffer every time data is copied to userspace. This
    computation is now used for applications setting SO_RCVBUF to update
    the maximum window scaling while ensuring that the receive buffer
    is within the application specified limit.
    
    Fixes: dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale")
    Signed-off-by: Sean Tranchetti <quic_stranche@xxxxxxxxxxx>
    Signed-off-by: Subash Abhinov Kasiviswanathan <quic_subashab@xxxxxxxxxxx>
    Reviewed-by: Eric Dumazet <edumazet@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 570e87ad9a56e..ecd521108559f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -754,8 +754,7 @@ 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) &&
-	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)) {
 		u64 rcvwin, grow;
 		int rcvbuf;
 
@@ -771,12 +770,22 @@ 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 (rcvbuf > sk->sk_rcvbuf) {
-			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
+		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));
+				/* 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 (clamp > tp->window_clamp)
+				WRITE_ONCE(tp->window_clamp, clamp);
 		}
 	}
 	tp->rcvq_space.space = copied;




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