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(223.70.159.239) by smtp.migadu.com with ESMTPS id e13d26de5bcb86be; Tue, 18 Aug 2026 09:48:38 +0000 X-Migadu-Flow: FLOW_OUT From: Gang Yan To: mptcp@lists.linux.dev Subject: [PATCH mptcp-next v2 2/5] mptcp: pm: change path_manager sysctl atomically Date: Tue, 18 Aug 2026 17:48:22 +0800 Message-ID: <20260818094825.48446-3-gang.yan@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260818094825.48446-1-gang.yan@linux.dev> References: <20260818094825.48446-1-gang.yan@linux.dev> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Gang Yan The per-netns path manager name is stored as an inline char[] buffer and updated via strscpy() from the sysctl handler; a concurrent reader can observe a half-written name (and KCSAN flags the race), which READ_ONCE() cannot fix for a multi-byte string. Following the tcp_congestion_control() model (and the scheduler change in the previous patch), store a pointer to the immutable struct mptcp_pm_ops instead of the name string: - mptcp_set_path_manager() looks the ops up and atomically swaps the pernet pointer with xchg(); - mptcp_get_path_manager() copies the ops name out under rcu_read_lock(); - the default ops is assigned in mptcp_pernet_set_defaults(). Assisted-by: Claude:GLM5.2 Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/626 Co-developed-by: Tao Cui Signed-off-by: Tao Cui Signed-off-by: Gang Yan --- net/mptcp/ctrl.c | 28 ++++++++++++++++++---------- net/mptcp/pm.c | 3 ++- net/mptcp/protocol.h | 3 +-- 3 files changed, 21 insertions(+), 13 deletions(-) diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c index 479b31eb3007..c0481b09c1a1 100644 --- a/net/mptcp/ctrl.c +++ b/net/mptcp/ctrl.c @@ -40,7 +40,7 @@ struct mptcp_pernet { u8 pm_type; u8 add_addr_v6_port_drop_ts; struct mptcp_sched_ops __rcu *scheduler; - char path_manager[MPTCP_PM_NAME_MAX]; + struct mptcp_pm_ops __rcu *path_manager; }; static struct mptcp_pernet *mptcp_get_pernet(const struct net *net) @@ -85,9 +85,14 @@ int mptcp_get_pm_type(const struct net *net) return mptcp_get_pernet(net)->pm_type; } -const char *mptcp_get_path_manager(const struct net *net) +void mptcp_get_path_manager(const struct net *net, char *name) { - return mptcp_get_pernet(net)->path_manager; + struct mptcp_pm_ops *pm_ops; + + rcu_read_lock(); + pm_ops = rcu_dereference(mptcp_get_pernet(net)->path_manager); + strscpy(name, pm_ops ? pm_ops->name : "kernel", MPTCP_PM_NAME_MAX); + rcu_read_unlock(); } void mptcp_get_scheduler(const struct net *net, char *name) @@ -119,8 +124,8 @@ static void mptcp_pernet_set_defaults(struct mptcp_pernet *pernet) pernet->pm_type = MPTCP_PM_TYPE_KERNEL; RCU_INIT_POINTER(pernet->scheduler, &mptcp_sched_default); + RCU_INIT_POINTER(pernet->path_manager, &mptcp_pm_kernel); - strscpy(pernet->path_manager, "kernel", sizeof(pernet->path_manager)); pernet->add_addr_v6_port_drop_ts = 1; } @@ -201,7 +206,7 @@ static int proc_blackhole_detect_timeout(const struct ctl_table *table, return ret; } -static int mptcp_set_path_manager(char *path_manager, const char *name) +static int mptcp_set_path_manager(struct mptcp_pernet *pernet, const char *name) { struct mptcp_pm_ops *pm_ops; int ret = 0; @@ -209,7 +214,7 @@ static int mptcp_set_path_manager(char *path_manager, const char *name) rcu_read_lock(); pm_ops = mptcp_pm_find(name); if (pm_ops) - strscpy(path_manager, name, MPTCP_PM_NAME_MAX); + xchg(&pernet->path_manager, pm_ops); else ret = -ENOENT; rcu_read_unlock(); @@ -223,7 +228,7 @@ static int proc_path_manager(const struct ctl_table *ctl, int write, struct mptcp_pernet *pernet = container_of(ctl->data, struct mptcp_pernet, path_manager); - char (*path_manager)[MPTCP_PM_NAME_MAX] = ctl->data; + struct mptcp_pm_ops *pm_ops; char pm_name[MPTCP_PM_NAME_MAX]; const struct ctl_table tbl = { .data = pm_name, @@ -231,11 +236,14 @@ static int proc_path_manager(const struct ctl_table *ctl, int write, }; int ret; - strscpy(pm_name, *path_manager, MPTCP_PM_NAME_MAX); + rcu_read_lock(); + pm_ops = rcu_dereference(pernet->path_manager); + strscpy(pm_name, pm_ops ? pm_ops->name : "kernel", MPTCP_PM_NAME_MAX); + rcu_read_unlock(); ret = proc_dostring(&tbl, write, buffer, lenp, ppos); if (write && ret == 0) { - ret = mptcp_set_path_manager(*path_manager, pm_name); + ret = mptcp_set_path_manager(pernet, pm_name); if (ret == 0) { u8 pm_type = __MPTCP_PM_TYPE_NR; @@ -267,7 +275,7 @@ static int proc_pm_type(const struct ctl_table *ctl, int write, pm_name = "kernel"; else if (pm_type == MPTCP_PM_TYPE_USERSPACE) pm_name = "userspace"; - mptcp_set_path_manager(pernet->path_manager, pm_name); + mptcp_set_path_manager(pernet, pm_name); } return ret; diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c index ba7c6f80a183..09f99bcd827c 100644 --- a/net/mptcp/pm.c +++ b/net/mptcp/pm.c @@ -1204,7 +1204,7 @@ void mptcp_pm_destroy(struct mptcp_sock *msk) void mptcp_pm_data_reset(struct mptcp_sock *msk) { const struct net *net = sock_net((struct sock *)msk); - const char *pm_name = mptcp_get_path_manager(net); + char pm_name[MPTCP_PM_NAME_MAX]; u8 pm_type = mptcp_get_pm_type(net); struct mptcp_pm_data *pm = &msk->pm; @@ -1213,6 +1213,7 @@ void mptcp_pm_data_reset(struct mptcp_sock *msk) pm->rm_list_rx.nr = 0; WRITE_ONCE(pm->pm_type, pm_type); + mptcp_get_path_manager(net, pm_name); rcu_read_lock(); mptcp_pm_ops_init(msk, pm_name); rcu_read_unlock(); diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index af79b3450ab7..99f447f2808f 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -802,7 +802,7 @@ int mptcp_allow_join_id0(const struct net *net); unsigned int mptcp_stale_loss_cnt(const struct net *net); unsigned int mptcp_close_timeout(const struct sock *sk); int mptcp_get_pm_type(const struct net *net); -const char *mptcp_get_path_manager(const struct net *net); +void mptcp_get_path_manager(const struct net *net, char *name); void mptcp_get_scheduler(const struct net *net, char *name); unsigned int mptcp_add_addr_v6_port_drop_ts(const struct net *net); @@ -1153,7 +1153,6 @@ int mptcp_pm_announce_addr(struct mptcp_sock *msk, bool echo); int mptcp_pm_remove_addr(struct mptcp_sock *msk, const struct mptcp_rm_list *rm_list); -/* the default path manager, used in mptcp_pm_unregister */ extern struct mptcp_pm_ops mptcp_pm_kernel; extern struct mptcp_sched_ops mptcp_sched_default; -- 2.43.0