mptcp: pm: ADD_ADDR 0 is not a new address

The ADD_ADDR 0 with the address from the initial subflow should not be
considered as a new address: this is not something new. If the host
receives it, it simply means that the address is available again.

When receiving an ADD_ADDR for the ID 0, the PM already doesn't consider
it as new by not incrementing the 'add_addr_accepted' counter. But the
'accept_addr' might not be set if the limit has already been reached:
this can be bypassed in this case. But before, it is important to check
that this ADD_ADDR for the ID 0 is for the same address as the initial
subflow. If not, it is not something that should happen, and the
ADD_ADDR can be ignored.

Note that if an ADD_ADDR is received while there is already a subflow
opened using the same address, this ADD_ADDR is ignored as well. It
means that if multiple ADD_ADDR for ID 0 are received, there will not be
any duplicated subflows created by the client.

Fixes: d0876b2284cf ("mptcp: add the incoming RM_ADDR support")
Cc: [email protected]
Reviewed-by: Mat Martineau <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 3f8dbde243f1..37f6dbcd8434 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -226,7 +226,9 @@ void mptcp_pm_add_addr_received(const struct sock *ssk,
 		} else {
 			__MPTCP_INC_STATS(sock_net((struct sock *)msk), MPTCP_MIB_ADDADDRDROP);
 		}
-	} else if (!READ_ONCE(pm->accept_addr)) {
+	/* id0 should not have a different address */
+	} else if ((addr->id == 0 && !mptcp_pm_nl_is_init_remote_addr(msk, addr)) ||
+		   (addr->id > 0 && !READ_ONCE(pm->accept_addr))) {
 		mptcp_pm_announce_addr(msk, addr, true);
 		mptcp_pm_add_addr_send_ack(msk);
 	} else if (mptcp_pm_schedule_work(msk, MPTCP_PM_ADD_ADDR_RECEIVED)) {