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")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/435
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
Note that there is no problem for the opposite event sequence.
---
 net/mptcp/pm_netlink.c | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 066bc855365c..617aad83eb87 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -396,19 +396,6 @@ 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.
  */
@@ -440,6 +427,16 @@ static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk,
 		msk->pm.subflows++;
 		addrs[i++] = remote;
 	} else {
+		DECLARE_BITMAP(unavail_id, MPTCP_PM_MAX_ADDR_ID + 1);
+
+		/* Forbit 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]);
@@ -447,11 +444,17 @@ static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk,
 			if (deny_id0 && !addrs[i].id)
 				continue;
 
+			if (test_bit(addrs[i].id, unavail_id))
+				continue;
+
 			if (!mptcp_pm_addr_families_match(sk, local, &addrs[i]))
 				continue;
 
-			if (!lookup_address_in_vec(addrs, i, &addrs[i]) &&
-			    msk->pm.subflows < subflows_max) {
+			if (msk->pm.subflows < subflows_max) {
+				/* forbit creating multiple address towards
+				 * this id
+				 */
+				__set_bit(addrs[i].id, unavail_id);
 				msk->pm.subflows++;
 				i++;
 			}
-- 
2.43.0

On Mon, 5 Feb 2024, Paolo Abeni wrote:

> 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")
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/435
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> Note that there is no problem for the opposite event sequence.
> ---
> net/mptcp/pm_netlink.c | 33 ++++++++++++++++++---------------
> 1 file changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
> index 066bc855365c..617aad83eb87 100644
> --- a/net/mptcp/pm_netlink.c
> +++ b/net/mptcp/pm_netlink.c
> @@ -396,19 +396,6 @@ 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.
>  */
> @@ -440,6 +427,16 @@ static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk,
> 		msk->pm.subflows++;
> 		addrs[i++] = remote;
> 	} else {
> +		DECLARE_BITMAP(unavail_id, MPTCP_PM_MAX_ADDR_ID + 1);
> +
> +		/* Forbit creation of new subflows matching existing

Looks ok code-wise, but s/forbit/forbid/ here and...

> +		 * 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]);
> @@ -447,11 +444,17 @@ static unsigned int fill_remote_addresses_vec(struct mptcp_sock *msk,
> 			if (deny_id0 && !addrs[i].id)
> 				continue;
>
> +			if (test_bit(addrs[i].id, unavail_id))
> +				continue;
> +
> 			if (!mptcp_pm_addr_families_match(sk, local, &addrs[i]))
> 				continue;
>
> -			if (!lookup_address_in_vec(addrs, i, &addrs[i]) &&
> -			    msk->pm.subflows < subflows_max) {
> +			if (msk->pm.subflows < subflows_max) {
> +				/* forbit creating multiple address towards

...here too. Or "Prevent" works too :)

- Mat

> +				 * this id
> +				 */
> +				__set_bit(addrs[i].id, unavail_id);
> 				msk->pm.subflows++;
> 				i++;
> 			}
> -- 
> 2.43.0
>
>
>