[PATCHv4 net] ipvs: fix races around est_mutex and est_cpulist

[Julian Anastasov <ja@xxxxxx>]

Sashiko reports for races and possible crash around
the usage of est_cpulist_valid and sysctl_est_cpulist.
The problem is that we do not lock est_mutex in some
places which can lead to wrong write ordering and
as result problems when calling cpumask_weight()
and cpumask_empty().

Fix them by moving the est_max_threads read/write under
locked est_mutex. Do the same for one ip_vs_est_reload_start()
call to protect the cpumask_empty() usage of sysctl_est_cpulist.

To remove the chance of deadlock while stopping the
estimation kthreads, keep the data structure for kthread 0
even after last estimator is removed and do not hold mutexes
while stopping this task. Now we will use a new flag 'needed'
to know when kthread 0 should run. The kthreads above 0
do not use mutexes, so stop them under est_mutex because
their kthread data still can be destroyed if they do not
serve estimators. Now all kthreads will be started by
the est_reload_work to properly serialize the stop/start
for kthread 0.

Reduce the use of service_mutex in ip_vs_est_calc_phase()
because under est_mutex we can safely walk est_kt_arr to
stop the kthreads above slot 0.

Finally, fix use-after-free for kd->est_row in
ip_vs_est_calc_phase(). est->ktrow should simply switch to
a delay value while estimator is linked to est_temp_list.

Link: 
https://sashiko.dev/#/patchset/20260331165015.2777765-1-longman%40redhat.com
Link: https://sashiko.dev/#/patchset/20260420171308.87192-1-ja%40ssi.bg
Link: https://sashiko.dev/#/patchset/20260422125123.40658-1-ja%40ssi.bg
Link: https://sashiko.dev/#/patchset/20260424175858.54752-1-ja%40ssi.bg
Fixes: f0be83d54217 ("ipvs: add est_cpulist and est_nice sysctl vars")
Signed-off-by: Julian Anastasov <ja@xxxxxx>
---
 include/net/ip_vs.h            |  3 +-
 net/netfilter/ipvs/ip_vs_ctl.c | 37 +++++++++++----
 net/netfilter/ipvs/ip_vs_est.c | 83 ++++++++++++++++++++--------------
 3 files changed, 79 insertions(+), 44 deletions(-)

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 72d325c81313..da375e372bee 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -491,6 +491,7 @@ struct ip_vs_est_kt_data {
        DECLARE_BITMAP(avail, IPVS_EST_NTICKS); /* tick has space for ests */
        unsigned long           est_timer;      /* estimation timer (jiffies) */
        struct ip_vs_stats      *calc_stats;    /* Used for calculation */
+       int                     needed;         /* task is needed */
        int                     tick_len[IPVS_EST_NTICKS];      /* est count */
        int                     id;             /* ktid per netns */
        int                     chain_max;      /* max ests per tick chain */
@@ -1884,7 +1885,7 @@ int ip_vs_start_estimator(struct netns_ipvs *ipvs, struct 
ip_vs_stats *stats);
 void ip_vs_stop_estimator(struct netns_ipvs *ipvs, struct ip_vs_stats *stats);
 void ip_vs_zero_estimator(struct ip_vs_stats *stats);
 void ip_vs_read_estimator(struct ip_vs_kstats *dst, struct ip_vs_stats *stats);
-void ip_vs_est_reload_start(struct netns_ipvs *ipvs);
+void ip_vs_est_reload_start(struct netns_ipvs *ipvs, bool restart);
 int ip_vs_est_kthread_start(struct netns_ipvs *ipvs,
                            struct ip_vs_est_kt_data *kd);
 void ip_vs_est_kthread_stop(struct ip_vs_est_kt_data *kd);
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index caec516856e9..d50ba6ce5743 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -261,12 +261,28 @@ static void est_reload_work_handler(struct work_struct 
*work)
                if (!kd)
                        continue;
                /* New config ? Stop kthread tasks */
-               if (genid != genid_done)
-                       ip_vs_est_kthread_stop(kd);
+               if (genid != genid_done) {
+                       if (!id) {
+                               /* Only we can stop kt 0 but not under mutex */
+                               mutex_unlock(&ipvs->est_mutex);
+                               ip_vs_est_kthread_stop(kd);
+                               mutex_lock(&ipvs->est_mutex);
+                               if (!READ_ONCE(ipvs->enable))
+                                       goto unlock;
+                               /* kd for kt 0 is never destroyed */
+                       } else {
+                               ip_vs_est_kthread_stop(kd);
+                       }
+               }
                if (!kd->task && !ip_vs_est_stopped(ipvs)) {
+                       bool start;
+
                        /* Do not start kthreads above 0 in calc phase */
-                       if ((!id || !ipvs->est_calc_phase) &&
-                           ip_vs_est_kthread_start(ipvs, kd) < 0)
+                       if (id)
+                               start = !ipvs->est_calc_phase;
+                       else
+                               start = kd->needed;
+                       if (start && ip_vs_est_kthread_start(ipvs, kd) < 0)
                                repeat = true;
                }
        }
@@ -1812,11 +1828,16 @@ ip_vs_add_service(struct netns_ipvs *ipvs, struct 
ip_vs_service_user_kern *u,
        *svc_p = svc;
 
        if (!READ_ONCE(ipvs->enable)) {
+               mutex_lock(&ipvs->est_mutex);
+
                /* Now there is a service - full throttle */
                WRITE_ONCE(ipvs->enable, 1);
 
+               ipvs->est_max_threads = ip_vs_est_max_threads(ipvs);
+
                /* Start estimation for first time */
-               ip_vs_est_reload_start(ipvs);
+               ip_vs_est_reload_start(ipvs, true);
+               mutex_unlock(&ipvs->est_mutex);
        }
 
        return 0;
@@ -2337,7 +2358,7 @@ static int ipvs_proc_est_cpumask_set(const struct 
ctl_table *table,
        /* est_max_threads may depend on cpulist size */
        ipvs->est_max_threads = ip_vs_est_max_threads(ipvs);
        ipvs->est_calc_phase = 1;
-       ip_vs_est_reload_start(ipvs);
+       ip_vs_est_reload_start(ipvs, true);
 
 unlock:
        mutex_unlock(&ipvs->est_mutex);
@@ -2417,7 +2438,7 @@ static int ipvs_proc_est_nice(const struct ctl_table 
*table, int write,
                        mutex_lock(&ipvs->est_mutex);
                        if (*valp != val) {
                                *valp = val;
-                               ip_vs_est_reload_start(ipvs);
+                               ip_vs_est_reload_start(ipvs, true);
                        }
                        mutex_unlock(&ipvs->est_mutex);
                }
@@ -2444,7 +2465,7 @@ static int ipvs_proc_run_estimation(const struct 
ctl_table *table, int write,
                mutex_lock(&ipvs->est_mutex);
                if (*valp != val) {
                        *valp = val;
-                       ip_vs_est_reload_start(ipvs);
+                       ip_vs_est_reload_start(ipvs, true);
                }
                mutex_unlock(&ipvs->est_mutex);
        }
diff --git a/net/netfilter/ipvs/ip_vs_est.c b/net/netfilter/ipvs/ip_vs_est.c
index 433ba3cab58c..ab09f5182951 100644
--- a/net/netfilter/ipvs/ip_vs_est.c
+++ b/net/netfilter/ipvs/ip_vs_est.c
@@ -68,6 +68,11 @@
     and the limit of estimators per kthread
   - est_add_ktid: ktid where to add new ests, can point to empty slot where
     we should add kt data
+  - data protected by service_mutex: est_temp_list, est_add_ktid,
+    est_kt_count(R/W), est_kt_arr(R/W), est_genid_done, kd->needed(R/W)
+  - data protected by est_mutex: est_genid, est_max_threads, 
sysctl_est_cpulist,
+    est_cpulist_valid, sysctl_est_nice, est_stopped, sysctl_run_estimation,
+    est_kt_count(R), est_kt_arr(R), kd->needed(R), kd->task (id > 0)
  */
 
 static struct lock_class_key __ipvs_est_key;
@@ -227,14 +232,17 @@ static int ip_vs_estimation_kthread(void *data)
 }
 
 /* Schedule stop/start for kthread tasks */
-void ip_vs_est_reload_start(struct netns_ipvs *ipvs)
+void ip_vs_est_reload_start(struct netns_ipvs *ipvs, bool restart)
 {
+       lockdep_assert_held(&ipvs->est_mutex);
+
        /* Ignore reloads before first service is added */
        if (!READ_ONCE(ipvs->enable))
                return;
        ip_vs_est_stopped_recalc(ipvs);
-       /* Bump the kthread configuration genid */
-       atomic_inc(&ipvs->est_genid);
+       /* Bump the kthread configuration genid if stopping is requested */
+       if (restart)
+               atomic_inc(&ipvs->est_genid);
        queue_delayed_work(system_long_wq, &ipvs->est_reload_work, 0);
 }
 
@@ -304,12 +312,17 @@ static int ip_vs_est_add_kthread(struct netns_ipvs *ipvs)
        void *arr = NULL;
        int i;
 
-       if ((unsigned long)ipvs->est_kt_count >= ipvs->est_max_threads &&
-           READ_ONCE(ipvs->enable) && ipvs->est_max_threads)
-               return -EINVAL;
-
        mutex_lock(&ipvs->est_mutex);
 
+       /* Allow kt 0 data to be created before the services are added
+        * and limit the kthreads when services are present.
+        */
+       if ((unsigned long)ipvs->est_kt_count >= ipvs->est_max_threads &&
+           READ_ONCE(ipvs->enable) && ipvs->est_max_threads) {
+               ret = -EINVAL;
+               goto out;
+       }
+
        for (i = 0; i < id; i++) {
                if (!ipvs->est_kt_arr[i])
                        break;
@@ -333,6 +346,7 @@ static int ip_vs_est_add_kthread(struct netns_ipvs *ipvs)
        kd->est_timer = jiffies;
        kd->id = id;
        ip_vs_est_set_params(ipvs, kd);
+       kd->needed = 1;
 
        /* Pre-allocate stats used in calc phase */
        if (!id && !kd->calc_stats) {
@@ -341,12 +355,8 @@ static int ip_vs_est_add_kthread(struct netns_ipvs *ipvs)
                        goto out;
        }
 
-       /* Start kthread tasks only when services are present */
-       if (READ_ONCE(ipvs->enable) && !ip_vs_est_stopped(ipvs)) {
-               ret = ip_vs_est_kthread_start(ipvs, kd);
-               if (ret < 0)
-                       goto out;
-       }
+       /* Request kthread to be started */
+       ip_vs_est_reload_start(ipvs, false);
 
        if (arr)
                ipvs->est_kt_count++;
@@ -482,12 +492,11 @@ static int ip_vs_enqueue_estimator(struct netns_ipvs 
*ipvs,
 /* Start estimation for stats */
 int ip_vs_start_estimator(struct netns_ipvs *ipvs, struct ip_vs_stats *stats)
 {
+       struct ip_vs_est_kt_data *kd = ipvs->est_kt_count > 0 ?
+                                      ipvs->est_kt_arr[0] : NULL;
        struct ip_vs_estimator *est = &stats->est;
        int ret;
 
-       if (!ipvs->est_max_threads && READ_ONCE(ipvs->enable))
-               ipvs->est_max_threads = ip_vs_est_max_threads(ipvs);
-
        est->ktid = -1;
        est->ktrow = IPVS_EST_NTICKS - 1;       /* Initial delay */
 
@@ -496,8 +505,15 @@ int ip_vs_start_estimator(struct netns_ipvs *ipvs, struct 
ip_vs_stats *stats)
         * will not allocate much memory, just for kt 0.
         */
        ret = 0;
-       if (!ipvs->est_kt_count || !ipvs->est_kt_arr[0])
+       if (!kd) {
                ret = ip_vs_est_add_kthread(ipvs);
+       } else if (!kd->needed) {
+               mutex_lock(&ipvs->est_mutex);
+               /* We have job for the kt 0 task */
+               kd->needed = 1;
+               ip_vs_est_reload_start(ipvs, true);
+               mutex_unlock(&ipvs->est_mutex);
+       }
        if (ret >= 0)
                hlist_add_head(&est->list, &ipvs->est_temp_list);
        else
@@ -578,16 +594,14 @@ void ip_vs_stop_estimator(struct netns_ipvs *ipvs, struct 
ip_vs_stats *stats)
        }
 
 end_kt0:
-       /* kt 0 is freed after all other kthreads and chains are empty */
+       /* kt 0 task is stopped after all other kt slots and chains are empty */
        if (ipvs->est_kt_count == 1 && hlist_empty(&ipvs->est_temp_list)) {
                kd = ipvs->est_kt_arr[0];
-               if (!kd || !kd->est_count) {
+               if (kd && !kd->est_count) {
                        mutex_lock(&ipvs->est_mutex);
-                       if (kd) {
-                               ip_vs_est_kthread_destroy(kd);
-                               ipvs->est_kt_arr[0] = NULL;
-                       }
-                       ipvs->est_kt_count--;
+                       /* Keep the kt0 data but request kthread_stop */
+                       kd->needed = 0;
+                       ip_vs_est_reload_start(ipvs, true);
                        mutex_unlock(&ipvs->est_mutex);
                        ipvs->est_add_ktid = 0;
                }
@@ -647,9 +661,9 @@ static int ip_vs_est_calc_limits(struct netns_ipvs *ipvs, 
int *chain_max)
        u64 val;
 
        INIT_HLIST_HEAD(&chain);
-       mutex_lock(&ipvs->service_mutex);
+       mutex_lock(&ipvs->est_mutex);
        kd = ipvs->est_kt_arr[0];
-       mutex_unlock(&ipvs->service_mutex);
+       mutex_unlock(&ipvs->est_mutex);
        s = kd ? kd->calc_stats : NULL;
        if (!s)
                goto out;
@@ -748,16 +762,16 @@ static void ip_vs_est_calc_phase(struct netns_ipvs *ipvs)
        if (!ip_vs_est_calc_limits(ipvs, &chain_max))
                return;
 
-       mutex_lock(&ipvs->service_mutex);
-
        /* Stop all other tasks, so that we can immediately move the
         * estimators to est_temp_list without RCU grace period
         */
        mutex_lock(&ipvs->est_mutex);
        for (id = 1; id < ipvs->est_kt_count; id++) {
                /* netns clean up started, abort */
-               if (!READ_ONCE(ipvs->enable))
-                       goto unlock2;
+               if (kthread_should_stop() || !READ_ONCE(ipvs->enable)) {
+                       mutex_unlock(&ipvs->est_mutex);
+                       return;
+               }
                kd = ipvs->est_kt_arr[id];
                if (!kd)
                        continue;
@@ -765,9 +779,11 @@ static void ip_vs_est_calc_phase(struct netns_ipvs *ipvs)
        }
        mutex_unlock(&ipvs->est_mutex);
 
+       mutex_lock(&ipvs->service_mutex);
+
        /* Move all estimators to est_temp_list but carefully,
         * all estimators and kthread data can be released while
-        * we reschedule. Even for kthread 0.
+        * we reschedule.
         */
        step = 0;
 
@@ -849,9 +865,7 @@ static void ip_vs_est_calc_phase(struct netns_ipvs *ipvs)
        ip_vs_stop_estimator(ipvs, stats);
        /* Tasks are stopped, move without RCU grace period */
        est->ktid = -1;
-       est->ktrow = row - kd->est_row;
-       if (est->ktrow < 0)
-               est->ktrow += IPVS_EST_NTICKS;
+       est->ktrow = delay;
        hlist_add_head(&est->list, &ipvs->est_temp_list);
        /* kd freed ? */
        if (last)
@@ -889,7 +903,6 @@ static void ip_vs_est_calc_phase(struct netns_ipvs *ipvs)
        if (genid == atomic_read(&ipvs->est_genid))
                ipvs->est_calc_phase = 0;
 
-unlock2:
        mutex_unlock(&ipvs->est_mutex);
 
 unlock:
-- 
2.53.0