FAILED: patch "[PATCH] mptcp: use MPJoinSynAckHMacFailure for SynAck HMAC failure" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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 <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x c4a99a921949cddc590b22bb14eeb23dffcc3ba6
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026051218-paging-duct-8343@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From c4a99a921949cddc590b22bb14eeb23dffcc3ba6 Mon Sep 17 00:00:00 2001
From: Shardul Bankar <[email protected]>
Date: Fri, 1 May 2026 21:35:34 +0200
Subject: [PATCH] mptcp: use MPJoinSynAckHMacFailure for SynAck HMAC failure

In subflow_finish_connect(), HMAC validation of the server's HMAC in SYN/ACK + MP_JOIN increments MPTCP_MIB_JOINACKMAC ("HMAC was wrong on ACK + MP_JOIN") on failure. The function processes the SYN/ACK, not the ACK; the matching MPTCP_MIB_JOINSYNACKMAC counter ("HMAC was wrong on SYN/ACK + MP_JOIN") exists but is not incremented anywhere in the tree.

The mirror site on the server, subflow_syn_recv_sock(), already uses JOINACKMAC correctly for ACK HMAC failure. Use JOINSYNACKMAC at the SYN/ACK validation site so each counter reflects the packet whose HMAC actually failed.

index e2cb9d23e4a0..bda6862264ca 100644
@@ -581,7 +581,7 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 			 subflow->backup);
 
 		if (!subflow_thmac_valid(subflow)) {
-			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINACKMAC);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKMAC);
 			subflow->reset_reason = MPTCP_RST_EMPTCP;
 			goto do_reset;
 		}