From: Gregory Detal <gregory.detal@gmail.com>

The current behavior is to accept any strings as inputs, this results in
an inconsistent result where an unexisting scheduler can be set:

  # sysctl -w net.mptcp.scheduler=notdefault
  net.mptcp.scheduler = notdefault

This patch changes this behavior by checking for existing scheduler
before accepting the input.

Fixes: e3b2870b6d22 ("mptcp: add a new sysctl scheduler")
Cc: stable@vger.kernel.org
Signed-off-by: Gregory Detal <gregory.detal@gmail.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Tested-by: Geliang Tang <geliang@kernel.org>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/ctrl.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 13fe0748dde8..2963ba84e2ee 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -96,6 +96,43 @@ static void mptcp_pernet_set_defaults(struct mptcp_pernet *pernet)
 }
 
 #ifdef CONFIG_SYSCTL
+static int mptcp_set_scheduler(const struct net *net, const char *name)
+{
+	struct mptcp_pernet *pernet = mptcp_get_pernet(net);
+	struct mptcp_sched_ops *sched;
+	int ret = 0;
+
+	rcu_read_lock();
+	sched = mptcp_sched_find(name);
+	if (sched)
+		strscpy(pernet->scheduler, name, MPTCP_SCHED_NAME_MAX);
+	else
+		ret = -ENOENT;
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static int proc_scheduler(struct ctl_table *ctl, int write,
+			  void *buffer, size_t *lenp, loff_t *ppos)
+{
+	const struct net *net = current->nsproxy->net_ns;
+	char val[MPTCP_SCHED_NAME_MAX];
+	struct ctl_table tbl = {
+		.data = val,
+		.maxlen = MPTCP_SCHED_NAME_MAX,
+	};
+	int ret;
+
+	strscpy(val, mptcp_get_scheduler(net), MPTCP_SCHED_NAME_MAX);
+
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+	if (write && ret == 0)
+		ret = mptcp_set_scheduler(net, val);
+
+	return ret;
+}
+
 static struct ctl_table mptcp_sysctl_table[] = {
 	{
 		.procname = "enabled",
@@ -148,7 +185,7 @@ static struct ctl_table mptcp_sysctl_table[] = {
 		.procname = "scheduler",
 		.maxlen	= MPTCP_SCHED_NAME_MAX,
 		.mode = 0644,
-		.proc_handler = proc_dostring,
+		.proc_handler = proc_scheduler,
 	},
 	{
 		.procname = "close_timeout",

---
base-commit: a26ff37e624d12e28077e5b24d2b264f62764ad6
change-id: 20240506-upstream-net-20240506-mptcp-sched-exist-6a1b91872a32

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>