[PATCH 5.15.y] mptcp: pm: check add_addr_accept_max before accepting new ADD_ADDR

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

commit 0137a3c7c2ea3f9df8ebfc65d78b4ba712a187bb upstream.

The limits might have changed in between, it is best to check them
before accepting new ADD_ADDR.

Fixes: d0876b2284cf ("mptcp: add the incoming RM_ADDR support")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-10-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in pm_netlink.c, because the context is different, but the
  same lines can still be modified to fix the issue. This is due to
  commit 322ea3778965 ("mptcp: pm: only mark 'subflow' endp as
  available") not being backported to this version. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index eeda20ec161c..ceeb5fbe8d35 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -772,8 +772,8 @@ static void mptcp_pm_nl_rm_addr_or_subflow(struct mptcp_sock *msk,
 			/* Note: if the subflow has been closed before, this
 			 * add_addr_accepted counter will not be decremented.
 			 */
-			msk->pm.add_addr_accepted--;
-			WRITE_ONCE(msk->pm.accept_addr, true);
+			if (--msk->pm.add_addr_accepted < mptcp_pm_get_add_addr_accept_max(msk))
+				WRITE_ONCE(msk->pm.accept_addr, true);
 		} else if (rm_type == MPTCP_MIB_RMSUBFLOW) {
 			msk->pm.local_addr_used--;
 		}
-- 
2.45.2