As mentioned in the 'Fixes' commit, the port flag is only supported by the 'signal' flag, and not by the 'subflow' one. Then if both the 'signal' and 'subflow' flags are set, the problem is the same: the feature cannot work with the 'subflow' flag.

Technically, if both the 'signal' and 'subflow' flags are set, it will be possible to create the listening socket, but not to establish a subflow using this source port. So better to explicitly deny it, not to create some confusions because the expected behaviour is not possible.

Fixes: 09f12c3ab7a5 ("mptcp: allow to use port and non-signal in set_flags") Cc: stable@vger.kernel.org Reviewed-by: Mat Martineau martineau@kernel.org 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 37954a0b087d..c921d07e5940 100644 --- a/net/mptcp/pm_netlink.c +++ b/net/mptcp/pm_netlink.c @@ -1328,8 +1328,8 @@ int mptcp_pm_nl_add_addr_doit(struct sk_buff *skb, struct genl_info *info) if (ret < 0) return ret;

- if (addr.addr.port && !(addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) { - GENL_SET_ERR_MSG(info, "flags must have signal when using port"); + if (addr.addr.port && !address_use_port(&addr)) { + GENL_SET_ERR_MSG(info, "flags must have signal and not subflow when using port"); return -EINVAL; }

Up to the 'Fixes' commit, having an endpoint with both the 'signal' and 'subflow' flags, resulted in the creation of a subflow and an address announcement using the address linked to this endpoint. After this commit, only the address announcement was done, ignoring the 'subflow' flag.

That's because the same bitmap is used for the two flags. It is OK to keep this single bitmap, the already selected local endpoint simply have to be re-used, but not via select_local_address() not to look at the just modified bitmap.

Note that it is unusual to set the two flags together: creating a new subflow using a new local address will implicitly advertise it to the other peer. So in theory, no need to advertise it explicitly as well. Maybe there are use-cases -- the subflow might not reach the other peer that way, we can ask the other peer to try initiating the new subflow without delay -- or very likely the user is confused, and put both flags "just to be sure at least the right one is set". Still, if it is allowed, the kernel should do what has been asked: using this endpoint to announce the address and to create a new subflow from it.

An alternative is to forbid the use of the two flags together, but that's probably too late, there are maybe use-cases, and it was working before. This patch will avoid people complaining subflows are not created using the endpoint they added with the 'subflow' and 'signal' flag.

Note that with the current patch, the subflow might not be created in some corner cases, e.g. if the 'subflows' limit was reached when sending the ADD_ADDR, but changed later on. It is probably not worth splitting id_avail_bitmap per target ('signal', 'subflow'), which will add another large field to the msk "just" to track (again) endpoints. Anyway, currently when the limits are changed, the kernel doesn't check if new subflows can be created or removed, because we would need to keep track of the received ADD_ADDR, and more. It sounds OK to assume that the limits should be properly configured before establishing new connections.

Fixes: 86e39e04482b ("mptcp: keep track of local endpoint still available for each msk") Cc: stable@vger.kernel.org Suggested-by: Paolo Abeni pabeni@redhat.com Reviewed-by: Mat Martineau martineau@kernel.org Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- net/mptcp/pm_netlink.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c index 2be7af377cda..4cae2aa7be5c 100644 --- a/net/mptcp/pm_netlink.c +++ b/net/mptcp/pm_netlink.c @@ -512,8 +512,8 @@ __lookup_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info)

static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk) { + struct mptcp_pm_addr_entry *local, *signal_and_subflow = NULL; struct sock *sk = (struct sock *)msk; - struct mptcp_pm_addr_entry *local; unsigned int add_addr_signal_max; unsigned int local_addr_max; struct pm_nl_pernet *pernet; @@ -579,6 +579,9 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk) msk->pm.add_addr_signaled++; mptcp_pm_announce_addr(msk, &local->addr, false); mptcp_pm_nl_addr_send_ack(msk); + + if (local->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW) + signal_and_subflow = local; }

subflow: @@ -589,9 +592,14 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk) bool fullmesh; int i, nr;

- local = select_local_address(pernet, msk); - if (!local) - break; + if (signal_and_subflow) { + local = signal_and_subflow; + signal_and_subflow = NULL; + } else { + local = select_local_address(pernet, msk); + if (!local) + break; + }

fullmesh = !!(local->flags & MPTCP_PM_ADDR_FLAG_FULLMESH);