FAILED: patch "[PATCH] sctp: do not update transport pathmtu if SPP_PMTUD_ENABLE is" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 02dc2ee7c7476dd831df63d2b10cc0a162a531f1 Mon Sep 17 00:00:00 2001
From: Xin Long <lucien.xin@gmail.com>
Date: Wed, 21 Jul 2021 14:45:54 -0400
Subject: [PATCH] sctp: do not update transport pathmtu if SPP_PMTUD_ENABLE is
 not set

Currently, in sctp_packet_config(), sctp_transport_pmtu_check() is
called to update transport pathmtu with dst's mtu when dst's mtu
has been changed by non sctp stack like xfrm.

However, this should only happen when SPP_PMTUD_ENABLE is set, no
matter where dst's mtu changed. This patch is to fix by checking
SPP_PMTUD_ENABLE flag before calling sctp_transport_pmtu_check().

Thanks Jacek for reporting and looking into this issue.

v1->v2:
  - add the missing "{" to fix the build error.

Fixes: 69fec325a643 ('Revert "sctp: remove sctp_transport_pmtu_check"')
Reported-by: Jacek Szafraniec <jacek.szafraniec@nokia.com>
Tested-by: Jacek Szafraniec <jacek.szafraniec@nokia.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sctp/output.c b/net/sctp/output.c
index 9032ce60d50e..4dfb5ea82b05 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -104,8 +104,8 @@ void sctp_packet_config(struct sctp_packet *packet, __u32 vtag,
 		if (asoc->param_flags & SPP_PMTUD_ENABLE)
 			sctp_assoc_sync_pmtu(asoc);
 	} else if (!sctp_transport_pl_enabled(tp) &&
-		   !sctp_transport_pmtu_check(tp)) {
-		if (asoc->param_flags & SPP_PMTUD_ENABLE)
+		   asoc->param_flags & SPP_PMTUD_ENABLE) {
+		if (!sctp_transport_pmtu_check(tp))
 			sctp_assoc_sync_pmtu(asoc);
 	}