From: Paolo Abeni <pabeni@redhat.com>

Fullmesh endpoints could end-up unexpectedly generating duplicate
subflows - same local and remote addresses - when multiple incoming
ADD_ADDR are processed before the PM creates the subflow for the local
endpoints.

Address the issue explicitly checking for duplicates at subflow
creation time.

To avoid a quadratic computational complexity, track the unavailable
remote address ids in a temporary bitmap and initialize such bitmap
with the remote ids of all the existing subflows matching the local
address currently processed.

The above allows additionally replacing the existing code checking
for duplicate entry in the current set with a simple bit test
operation.

Fixes: 2843ff6f36db ("mptcp: remote addresses fullmesh")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/435
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 045e9d812868a2d80b7a57b224ce8009444b7bbc)
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Notes:
 - conflicts in pm_netlink.c because b9d69db87fb7 ("mptcp: let the
   in-kernel PM use mixed IPv4 and IPv6 addresses") is not in v6.1, and
   it introduced an extra check (mptcp_pm_addr_families_match()) in the
   modified context we don't need here.
 - we need the new 'local' parameter from b9d69db87fb7 ("mptcp: let the
   in-kernel PM use mixed IPv4 and IPv6 addresses").
---
 net/mptcp/pm_netlink.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 582d0c641ed1..3328870b0c1f 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -407,23 +407,12 @@ void mptcp_pm_free_anno_list(struct mptcp_sock *msk)
 	}
 }
 
-static bool lookup_address_in_vec(const struct mptcp_addr_info *addrs, unsigned int nr,
-				  const struct mptcp_addr_info *addr)
-{
-	int i;
-
-	for (i = 0; i < nr; i++) {
-		if (addrs[i].id == addr->id)
-			return true;
-	}
-
-	return false;
-}
-
 /* Fill all the remote addresses into the array addrs[],
  * and return the array size.
  */
-static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk, bool fullmesh,
+static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk,
+					      struct mptcp_addr_info *local,
+					      bool fullmesh,
 					      struct mptcp_addr_info *addrs)
 {
 	bool deny_id0 = READ_ONCE(msk->pm.remote_deny_join_id0);
@@ -446,6 +435,16 @@ static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk, bool fullm
 		msk->pm.subflows++;
 		addrs[i++] = remote;
 	} else {
+		DECLARE_BITMAP(unavail_id, MPTCP_PM_MAX_ADDR_ID + 1);
+
+		/* Forbid creation of new subflows matching existing
+		 * ones, possibly already created by incoming ADD_ADDR
+		 */
+		bitmap_zero(unavail_id, MPTCP_PM_MAX_ADDR_ID + 1);
+		mptcp_for_each_subflow(msk, subflow)
+			if (READ_ONCE(subflow->local_id) == local->id)
+				__set_bit(subflow->remote_id, unavail_id);
+
 		mptcp_for_each_subflow(msk, subflow) {
 			ssk = mptcp_subflow_tcp_sock(subflow);
 			remote_address((struct sock_common *)ssk, &addrs[i]);
@@ -453,8 +452,11 @@ static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk, bool fullm
 			if (deny_id0 && !addrs[i].id)
 				continue;
 
-			if (!lookup_address_in_vec(addrs, i, &addrs[i]) &&
-			    msk->pm.subflows < subflows_max) {
+			if (msk->pm.subflows < subflows_max) {
+				/* forbid creating multiple address towards
+				 * this id
+				 */
+				__set_bit(addrs[i].id, unavail_id);
 				msk->pm.subflows++;
 				i++;
 			}
@@ -603,7 +605,7 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 		fullmesh = !!(local->flags & MPTCP_PM_ADDR_FLAG_FULLMESH);
 
 		msk->pm.local_addr_used++;
-		nr = fill_remote_addresses_vec(msk, fullmesh, addrs);
+		nr = fill_remote_addresses_vec(msk, &local->addr, fullmesh, addrs);
 		if (nr)
 			__clear_bit(local->addr.id, msk->pm.id_avail_bitmap);
 		spin_unlock_bh(&msk->pm.lock);
-- 
2.43.0