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KCSAN reported a data-race on the `ipvs->enable` flag, which is
written in the control path and read concurrently from many other
contexts.
Following a suggestion by Julian, this patch fixes the race by
converting all accesses to use `WRITE_ONCE()/READ_ONCE()`.
This lightweight approach ensures atomic access and acts as a
compiler barrier, preventing unsafe optimizations where the flag
is checked in loops (e.g., in ip_vs_est.c).
Additionally, the `enable` checks in the fast-path hooks
(`ip_vs_in_hook`, `ip_vs_out_hook`, `ip_vs_forward_icmp`) are
removed. They are considered unnecessary because the `enable=0`
condition they check for can only occur in two rare and non-fatal
scenarios: 1) after hooks are registered but before the flag is set,
and 2) after hooks are unregistered on cleanup_net. In the worst
case, a single packet might be mishandled (e.g., dropped), which
does not lead to a system crash or data corruption. Adding a check
in the performance-critical fast-path to handle this harmless
condition is not a worthwhile trade-off.
Reported-by: syzbot+1651b5234028c294c339@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=1651b5234028c294c339
Suggested-by: Julian Anastasov <ja@xxxxxx>
Link:
https://lore.kernel.org/lvs-devel/2189fc62-e51e-78c9-d1de-d35b8e3657e3@xxxxxx/
Signed-off-by: Zhang Tengfei <zhtfdev@xxxxxxxxx>
---
v2:
- Switched from atomic_t to the suggested READ_ONCE()/WRITE_ONCE().
- Removed obsolete checks from the packet processing hooks.
- Polished commit message based on feedback from maintainers.
---
net/netfilter/ipvs/ip_vs_conn.c | 4 ++--
net/netfilter/ipvs/ip_vs_core.c | 11 ++++-------
net/netfilter/ipvs/ip_vs_ctl.c | 6 +++---
net/netfilter/ipvs/ip_vs_est.c | 16 ++++++++--------
4 files changed, 17 insertions(+), 20 deletions(-)
diff --git a/net/netfilter/ipvs/ip_vs_conn.c b/net/netfilter/ipvs/ip_vs_conn.c
index 965f3c8e5..37ebb0cb6 100644
--- a/net/netfilter/ipvs/ip_vs_conn.c
+++ b/net/netfilter/ipvs/ip_vs_conn.c
@@ -885,7 +885,7 @@ static void ip_vs_conn_expire(struct timer_list *t)
* conntrack cleanup for the net.
*/
smp_rmb();
- if (ipvs->enable)
+ if (READ_ONCE(ipvs->enable))
ip_vs_conn_drop_conntrack(cp);
}
@@ -1439,7 +1439,7 @@ void ip_vs_expire_nodest_conn_flush(struct netns_ipvs
*ipvs)
cond_resched_rcu();
/* netns clean up started, abort delayed work */
- if (!ipvs->enable)
+ if (!READ_ONCE(ipvs->enable))
break;
}
rcu_read_unlock();
diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index c7a8a08b7..5ea7ab8bf 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -1353,9 +1353,6 @@ ip_vs_out_hook(void *priv, struct sk_buff *skb, const
struct nf_hook_state *stat
if (unlikely(!skb_dst(skb)))
return NF_ACCEPT;
- if (!ipvs->enable)
- return NF_ACCEPT;
-
ip_vs_fill_iph_skb(af, skb, false, &iph);
#ifdef CONFIG_IP_VS_IPV6
if (af == AF_INET6) {
@@ -1940,7 +1937,7 @@ ip_vs_in_hook(void *priv, struct sk_buff *skb, const
struct nf_hook_state *state
return NF_ACCEPT;
}
/* ipvs enabled in this netns ? */
- if (unlikely(sysctl_backup_only(ipvs) || !ipvs->enable))
+ if (unlikely(sysctl_backup_only(ipvs)))
return NF_ACCEPT;
ip_vs_fill_iph_skb(af, skb, false, &iph);
@@ -2108,7 +2105,7 @@ ip_vs_forward_icmp(void *priv, struct sk_buff *skb,
int r;
/* ipvs enabled in this netns ? */
- if (unlikely(sysctl_backup_only(ipvs) || !ipvs->enable))
+ if (unlikely(sysctl_backup_only(ipvs)))
return NF_ACCEPT;
if (state->pf == NFPROTO_IPV4) {
@@ -2295,7 +2292,7 @@ static int __net_init __ip_vs_init(struct net *net)
return -ENOMEM;
/* Hold the beast until a service is registered */
- ipvs->enable = 0;
+ WRITE_ONCE(ipvs->enable, 0);
ipvs->net = net;
/* Counters used for creating unique names */
ipvs->gen = atomic_read(&ipvs_netns_cnt);
@@ -2367,7 +2364,7 @@ static void __net_exit __ip_vs_dev_cleanup_batch(struct
list_head *net_list)
ipvs = net_ipvs(net);
ip_vs_unregister_hooks(ipvs, AF_INET);
ip_vs_unregister_hooks(ipvs, AF_INET6);
- ipvs->enable = 0; /* Disable packet reception */
+ WRITE_ONCE(ipvs->enable, 0); /* Disable packet reception */
smp_wmb();
ip_vs_sync_net_cleanup(ipvs);
}
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 6a6fc4478..4c8fa22be 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -256,7 +256,7 @@ static void est_reload_work_handler(struct work_struct
*work)
struct ip_vs_est_kt_data *kd = ipvs->est_kt_arr[id];
/* netns clean up started, abort delayed work */
- if (!ipvs->enable)
+ if (!READ_ONCE(ipvs->enable))
goto unlock;
if (!kd)
continue;
@@ -1483,9 +1483,9 @@ ip_vs_add_service(struct netns_ipvs *ipvs, struct
ip_vs_service_user_kern *u,
*svc_p = svc;
- if (!ipvs->enable) {
+ if (!READ_ONCE(ipvs->enable)) {
/* Now there is a service - full throttle */
- ipvs->enable = 1;
+ WRITE_ONCE(ipvs->enable, 1);
/* Start estimation for first time */
ip_vs_est_reload_start(ipvs);
diff --git a/net/netfilter/ipvs/ip_vs_est.c b/net/netfilter/ipvs/ip_vs_est.c
index 15049b826..93a925f1e 100644
--- a/net/netfilter/ipvs/ip_vs_est.c
+++ b/net/netfilter/ipvs/ip_vs_est.c
@@ -231,7 +231,7 @@ static int ip_vs_estimation_kthread(void *data)
void ip_vs_est_reload_start(struct netns_ipvs *ipvs)
{
/* Ignore reloads before first service is added */
- if (!ipvs->enable)
+ if (!READ_ONCE(ipvs->enable))
return;
ip_vs_est_stopped_recalc(ipvs);
/* Bump the kthread configuration genid */
@@ -306,7 +306,7 @@ static int ip_vs_est_add_kthread(struct netns_ipvs *ipvs)
int i;
if ((unsigned long)ipvs->est_kt_count >= ipvs->est_max_threads &&
- ipvs->enable && ipvs->est_max_threads)
+ READ_ONCE(ipvs->enable) && ipvs->est_max_threads)
return -EINVAL;
mutex_lock(&ipvs->est_mutex);
@@ -343,7 +343,7 @@ static int ip_vs_est_add_kthread(struct netns_ipvs *ipvs)
}
/* Start kthread tasks only when services are present */
- if (ipvs->enable && !ip_vs_est_stopped(ipvs)) {
+ if (READ_ONCE(ipvs->enable) && !ip_vs_est_stopped(ipvs)) {
ret = ip_vs_est_kthread_start(ipvs, kd);
if (ret < 0)
goto out;
@@ -486,7 +486,7 @@ int ip_vs_start_estimator(struct netns_ipvs *ipvs, struct
ip_vs_stats *stats)
struct ip_vs_estimator *est = &stats->est;
int ret;
- if (!ipvs->est_max_threads && ipvs->enable)
+ if (!ipvs->est_max_threads && READ_ONCE(ipvs->enable))
ipvs->est_max_threads = ip_vs_est_max_threads(ipvs);
est->ktid = -1;
@@ -663,7 +663,7 @@ static int ip_vs_est_calc_limits(struct netns_ipvs *ipvs,
int *chain_max)
/* Wait for cpufreq frequency transition */
wait_event_idle_timeout(wq, kthread_should_stop(),
HZ / 50);
- if (!ipvs->enable || kthread_should_stop())
+ if (!READ_ONCE(ipvs->enable) || kthread_should_stop())
goto stop;
}
@@ -681,7 +681,7 @@ static int ip_vs_est_calc_limits(struct netns_ipvs *ipvs,
int *chain_max)
rcu_read_unlock();
local_bh_enable();
- if (!ipvs->enable || kthread_should_stop())
+ if (!READ_ONCE(ipvs->enable) || kthread_should_stop())
goto stop;
cond_resched();
@@ -757,7 +757,7 @@ static void ip_vs_est_calc_phase(struct netns_ipvs *ipvs)
mutex_lock(&ipvs->est_mutex);
for (id = 1; id < ipvs->est_kt_count; id++) {
/* netns clean up started, abort */
- if (!ipvs->enable)
+ if (!READ_ONCE(ipvs->enable))
goto unlock2;
kd = ipvs->est_kt_arr[id];
if (!kd)
@@ -787,7 +787,7 @@ static void ip_vs_est_calc_phase(struct netns_ipvs *ipvs)
id = ipvs->est_kt_count;
next_kt:
- if (!ipvs->enable || kthread_should_stop())
+ if (!READ_ONCE(ipvs->enable) || kthread_should_stop())
goto unlock;
id--;
if (id < 0)
--
2.34.1
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