5.15-stable review patch. If anyone has any objections, please let me know.
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From: "Matthieu Baerts (NGI0)" matttbe@kernel.org
commit 4b1ff850e0c1aacc23e923ed22989b827b9808f9 upstream.
When servers set the C-flag in their MP_CAPABLE to tell clients not to create subflows to the initial address and port, clients will likely not use their other endpoints. That's because the in-kernel path-manager uses the 'subflow' endpoints to create subflows only to the initial address and port.
If the limits have not been modified to accept ADD_ADDR, the client doesn't try to establish new subflows. If the limits accept ADD_ADDR, the routing routes will be used to select the source IP.
The C-flag is typically set when the server is operating behind a legacy Layer 4 load balancer, or using anycast IP address. Clients having their different 'subflow' endpoints setup, don't end up creating multiple subflows as expected, and causing some deployment issues.
A special case is then added here: when servers set the C-flag in the MPC and directly sends an ADD_ADDR, this single ADD_ADDR is accepted. The 'subflows' endpoints will then be used with this new remote IP and port. This exception is only allowed when the ADD_ADDR is sent immediately after the 3WHS, and makes the client switching to the 'fully established' mode. After that, 'select_local_address()' will not be able to find any subflows, because 'id_avail_bitmap' will be filled in mptcp_pm_create_subflow_or_signal_addr(), when switching to 'fully established' mode.
Fixes: df377be38725 ("mptcp: add deny_join_id0 in mptcp_options_received") Cc: stable@vger.kernel.org Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/536 Reviewed-by: Geliang Tang geliang@kernel.org Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-1-ad126cc... Signed-off-by: Jakub Kicinski kuba@kernel.org [ Conflict in pm.c, because commit 498d7d8b75f1 ("mptcp: pm: remove '_nl' from mptcp_pm_nl_is_init_remote_addr") renamed an helper in the context, and it is not in this version. The same new code can be applied at the same place. Another conflict in pm.c, because commit 4d25247d3ae4 ("mptcp: bypass in-kernel PM restrictions for non-kernel PMs") switched the modified 'if' statement to an 'else if', and is not in this version. The same modification can still be applied. Conflict in pm_kernel.c, because the modified code has been moved from pm_netlink.c to pm_kernel.c in commit 8617e85e04bd ("mptcp: pm: split in-kernel PM specific code"), which is not in this version. The resolution is easy: simply by applying the patch where 'pm_kernel.c' has been replaced 'pm_netlink.c'. Conflict in pm_netlink.c, because commit b83fbca1b4c9 ("mptcp: pm: reduce entries iterations on connect") is not in this version. Instead of using the 'locals' variable (struct mptcp_pm_local *) from the new version and embedding a "struct mptcp_addr_info", we can simply continue to use the 'addrs' variable (struct mptcp_addr_info *). Because commit b9d69db87fb7 ("mptcp: let the in-kernel PM use mixed IPv4 and IPv6 addresses") is not in this version, it is also required to pass an extra parameter to fill_local_addresses_vec(): struct mptcp_addr_info *remote, which is available from the caller side. Same with commit 4638de5aefe5 ("mptcp: handle local addrs announced by userspace PMs") adding the 'mptcp_' prefix to addresses_equal(). Conflict in protocol.h, because commit af3dc0ad3167 ("mptcp: Remove unused declaration mptcp_sockopt_sync()") is not in this version and it removed one line in the context. The resolution is easy because the new function can still be added at the same place. A similar conflict has been resolved due to commit 95d686517884 ("mptcp: fix subflow accounting on close"). ] Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org
Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/mptcp/pm.c | 7 +++++-- net/mptcp/pm_netlink.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++- net/mptcp/protocol.h | 8 ++++++++ 3 files changed, 61 insertions(+), 3 deletions(-)
--- a/net/mptcp/pm.c +++ b/net/mptcp/pm.c @@ -189,9 +189,12 @@ void mptcp_pm_add_addr_received(struct m
spin_lock_bh(&pm->lock);
- /* id0 should not have a different address */ + /* - id0 should not have a different address + * - special case for C-flag: linked to fill_local_addresses_vec() + */ if ((addr->id == 0 && !mptcp_pm_nl_is_init_remote_addr(msk, addr)) || - (addr->id > 0 && !READ_ONCE(pm->accept_addr))) { + (addr->id > 0 && !READ_ONCE(pm->accept_addr) && + !mptcp_pm_add_addr_c_flag_case(msk))) { 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)) { --- a/net/mptcp/pm_netlink.c +++ b/net/mptcp/pm_netlink.c @@ -571,6 +571,7 @@ static void mptcp_pm_nl_subflow_establis * and return the array size. */ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk, + struct mptcp_addr_info *remote, struct mptcp_addr_info *addrs) { struct sock *sk = (struct sock *)msk; @@ -578,10 +579,12 @@ static unsigned int fill_local_addresses struct mptcp_addr_info mpc_addr; struct pm_nl_pernet *pernet; unsigned int subflows_max; + bool c_flag_case; int i = 0;
pernet = net_generic(sock_net(sk), pm_nl_pernet_id); subflows_max = mptcp_pm_get_subflows_max(msk); + c_flag_case = remote->id && mptcp_pm_add_addr_c_flag_case(msk);
mptcp_local_address((struct sock_common *)msk, &mpc_addr);
@@ -605,6 +608,10 @@ static unsigned int fill_local_addresses msk->pm.subflows++; addrs[i] = entry->addr;
+ if (c_flag_case && + (entry->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW)) + msk->pm.local_addr_used++; + /* Special case for ID0: set the correct ID */ if (addresses_equal(&entry->addr, &mpc_addr, entry->addr.port)) addrs[i].id = 0; @@ -614,6 +621,46 @@ static unsigned int fill_local_addresses } rcu_read_unlock();
+ /* Special case: peer sets the C flag, accept one ADD_ADDR if default + * limits are used -- accepting no ADD_ADDR -- and use subflow endpoints + */ + if (!i && c_flag_case) { + unsigned int local_addr_max = mptcp_pm_get_local_addr_max(msk); + + rcu_read_lock(); + __mptcp_flush_join_list(msk); + list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) { + if (!(entry->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW)) + continue; + + if (entry->addr.family != sk->sk_family) { +#if IS_ENABLED(CONFIG_MPTCP_IPV6) + if ((entry->addr.family == AF_INET && + !ipv6_addr_v4mapped(&sk->sk_v6_daddr)) || + (sk->sk_family == AF_INET && + !ipv6_addr_v4mapped(&entry->addr.addr6))) +#endif + continue; + } + + /* avoid any address already in use by subflows and + * pending join + */ + if (!lookup_subflow_by_saddr(&msk->conn_list, &entry->addr) && + msk->pm.local_addr_used < local_addr_max && + msk->pm.subflows < subflows_max) { + addrs[i] = entry->addr; + + msk->pm.local_addr_used++; + msk->pm.subflows++; + i++; + } + } + rcu_read_unlock(); + + return i; + } + /* If the array is empty, fill in the single * 'IPADDRANY' local address */ @@ -661,7 +708,7 @@ static void mptcp_pm_nl_add_addr_receive /* connect to the specified remote address, using whatever * local address the routing configuration will pick. */ - nr = fill_local_addresses_vec(msk, addrs); + nr = fill_local_addresses_vec(msk, &remote, addrs);
spin_unlock_bh(&msk->pm.lock); for (i = 0; i < nr; i++) --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -846,6 +846,14 @@ unsigned int mptcp_pm_get_add_addr_accep unsigned int mptcp_pm_get_subflows_max(const struct mptcp_sock *msk); unsigned int mptcp_pm_get_local_addr_max(const struct mptcp_sock *msk);
+static inline bool mptcp_pm_add_addr_c_flag_case(struct mptcp_sock *msk) +{ + return READ_ONCE(msk->pm.remote_deny_join_id0) && + msk->pm.local_addr_used == 0 && + mptcp_pm_get_add_addr_accept_max(msk) == 0 && + msk->pm.subflows < mptcp_pm_get_subflows_max(msk); +} + void mptcp_sockopt_sync(struct mptcp_sock *msk, struct sock *ssk); void mptcp_sockopt_sync_all(struct mptcp_sock *msk);