[PATCH 2/2] ipvs: Guard access of HK_TYPE_KTHREAD cpumask with RCU

[Waiman Long <longman@redhat.com>]

The ip_vs_ctl.c file and the associated ip_vs.h file are the only places
in the kernel where HK_TYPE_KTHREAD cpumask is being retrieved and used.
Now that HK_TYPE_KTHREAD/HK_TYPE_DOMAIN cpumask can be changed at run
time. We need to use RCU to guard access to this cpumask to avoid a
potential UAF problem as the returned cpumask may be freed before it
is being used.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/net/ip_vs.h            | 20 ++++++++++++++++----
 net/netfilter/ipvs/ip_vs_ctl.c | 13 ++++++++-----
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 29a36709e7f3..17c85a575ef4 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -1155,7 +1155,7 @@ static inline int sysctl_run_estimation(struct netns_ipvs *ipvs)
 	return ipvs->sysctl_run_estimation;
 }
 
-static inline const struct cpumask *sysctl_est_cpulist(struct netns_ipvs *ipvs)
+static inline const struct cpumask *__sysctl_est_cpulist(struct netns_ipvs *ipvs)
 {
 	if (ipvs->est_cpulist_valid)
 		return ipvs->sysctl_est_cpulist;
@@ -1273,7 +1273,7 @@ static inline int sysctl_run_estimation(struct netns_ipvs *ipvs)
 	return 1;
 }
 
-static inline const struct cpumask *sysctl_est_cpulist(struct netns_ipvs *ipvs)
+static inline const struct cpumask *__sysctl_est_cpulist(struct netns_ipvs *ipvs)
 {
 	return housekeeping_cpumask(HK_TYPE_KTHREAD);
 }
@@ -1290,6 +1290,18 @@ static inline int sysctl_est_nice(struct netns_ipvs *ipvs)
 
 #endif
 
+static inline bool sysctl_est_cpulist_empty(struct netns_ipvs *ipvs)
+{
+	guard(rcu)();
+	return cpumask_empty(__sysctl_est_cpulist(ipvs));
+}
+
+static inline unsigned int sysctl_est_cpulist_weight(struct netns_ipvs *ipvs)
+{
+	guard(rcu)();
+	return cpumask_weight(__sysctl_est_cpulist(ipvs));
+}
+
 /* IPVS core functions
  * (from ip_vs_core.c)
  */
@@ -1604,7 +1616,7 @@ static inline void ip_vs_est_stopped_recalc(struct netns_ipvs *ipvs)
 	/* Stop tasks while cpulist is empty or if disabled with flag */
 	ipvs->est_stopped = !sysctl_run_estimation(ipvs) ||
 			    (ipvs->est_cpulist_valid &&
-			     cpumask_empty(sysctl_est_cpulist(ipvs)));
+			     sysctl_est_cpulist_empty(ipvs));
 #endif
 }
 
@@ -1620,7 +1632,7 @@ static inline bool ip_vs_est_stopped(struct netns_ipvs *ipvs)
 static inline int ip_vs_est_max_threads(struct netns_ipvs *ipvs)
 {
 	unsigned int limit = IPVS_EST_CPU_KTHREADS *
-			     cpumask_weight(sysctl_est_cpulist(ipvs));
+			     sysctl_est_cpulist_weight(ipvs);
 
 	return max(1U, limit);
 }
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 35642de2a0fe..f38a2e2a9dc5 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -1973,11 +1973,14 @@ static int ipvs_proc_est_cpumask_get(const struct ctl_table *table,
 
 	mutex_lock(&ipvs->est_mutex);
 
-	if (ipvs->est_cpulist_valid)
-		mask = *valp;
-	else
-		mask = (struct cpumask *)housekeeping_cpumask(HK_TYPE_KTHREAD);
-	ret = scnprintf(buffer, size, "%*pbl\n", cpumask_pr_args(mask));
+	/* HK_TYPE_KTHREAD cpumask needs RCU protection */
+	scoped_guard(rcu) {
+		if (ipvs->est_cpulist_valid)
+			mask = *valp;
+		else
+			mask = (struct cpumask *)housekeeping_cpumask(HK_TYPE_KTHREAD);
+		ret = scnprintf(buffer, size, "%*pbl\n", cpumask_pr_args(mask));
+	}
 
 	mutex_unlock(&ipvs->est_mutex);
 
-- 
2.53.0