Re: [PATCH-next v2 2/2] ipvs: Guard access of HK_TYPE_KTHREAD cpumask with RCU

Waiman Long
2026-04-01T15:13:25Z

On 4/1/26 8:54 AM, Frederic Weisbecker wrote:
> Le Tue, Mar 31, 2026 at 12:50:15PM -0400, Waiman Long a écrit :
>> 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.
>>
>> Signed-off-by: Waiman Long <longman@redhat.com>
> Oh I see you're handling a few concerns here. But it's too late, the previous
> patch broke bisection.
Good point. So I have to either reverse the patch order, or just change
HK_TYPE_KTHREAD to HK_TYPE_DOMAIN & drop the first one.
>
>> ---
>> 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 72d325c81313..7bda92fd3fe6 100644
>> --- a/include/net/ip_vs.h
>> +++ b/include/net/ip_vs.h
>> @@ -1411,7 +1411,7 @@ 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;
>> @@ -1529,7 +1529,7 @@ 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);
>> }
>> @@ -1564,6 +1564,18 @@ 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)
>> */
>> @@ -1895,7 +1907,7 @@ 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));
> It's not needed, if ipvs->est_cpulist_valid, sysctl_est_cpulist() doesn't
> refer to housekeeping.
Right.
>> #endif
>> }
>>
>> @@ -1911,7 +1923,7 @@ 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);
> That probably works for callers ip_vs_start_estimator().
>
> But this is not handling the core issue that related kthreads should be updated,
> as is done in ipvs_proc_est_cpumask_set(), when HK_TYPE_DOMAIN mask changes.

If ipvs_proc_est_cpumask_set() has been called, the real affinity should
be the intersection of the given cpumask and HK_TYPE_DOMAIN cpumask. Is
that what you are referring to?

Cheers,
Longman

>
>>
>> return max(1U, limit);
>> }
>> diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
>> index 032425025d88..e253a1ceef48 100644
>> --- a/net/netfilter/ipvs/ip_vs_ctl.c
>> +++ b/net/netfilter/ipvs/ip_vs_ctl.c
>> @@ -2338,11 +2338,14 @@ 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));
>> + }
> And that works.
>
> Thanks.
>
>>
>> mutex_unlock(&ipvs->est_mutex);
>>
>> --
>> 2.53.0
>>