[PATCH net 7/8] ipvs: Guard access of HK_TYPE_KTHREAD cpumask with RCU

Pablo Neira Ayuso
2026-05-05T00:17:09Z

From: 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.

We can replace HK_TYPE_KTHREAD by HK_TYPE_DOMAIN as they are aliases
of each other, but keeping the HK_TYPE_KTHREAD name can highlight the
fact that it is the kthread initiated by ipvs that is being controlled.

Fixes: 03ff73510169 ("cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
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 d28ad8a0541f..02762ce73a0c 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -1412,7 +1412,7 @@ 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;
@@ -1530,7 +1530,7 @@ 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);
}
@@ -1565,6 +1565,18 @@ static inline int sysctl_svc_lfactor(struct netns_ipvs *ipvs)
return READ_ONCE(ipvs->sysctl_svc_lfactor);
}

+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)
*/
@@ -1904,7 +1916,7 @@ 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
}

@@ -1920,7 +1932,7 @@ 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 5c9f8e0e238f..c7c7f6a7a9f6 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -2394,11 +2394,14 @@ 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);

--
2.47.3