[PATCH] ipvs: fix racy memcpy in proc_do_sync_threshold

When two threads run proc_do_sync_threshold() in parallel,
data races could happen between the two memcpy():

Thread-1			Thread-2
memcpy(val, valp, sizeof(val));
				memcpy(valp, val, sizeof(val));

This race might mess up the (struct ctl_table *) table->data,
so we add a mutex lock to serilize them, as discussed in [1].

[1] https://archive.linuxvirtualserver.org/html/lvs-devel/2023-08/msg00031.html

Signed-off-by: Sishuai Gong <[email protected]>
---
 net/netfilter/ipvs/ip_vs_ctl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 62606fb44d02..4bb0d90eca1c 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -1876,6 +1876,7 @@ static int
 proc_do_sync_threshold(struct ctl_table *table, int write,
 		       void *buffer, size_t *lenp, loff_t *ppos)
 {
+	struct netns_ipvs *ipvs = table->extra2;
 	int *valp = table->data;
 	int val[2];
 	int rc;
@@ -1885,6 +1886,7 @@ proc_do_sync_threshold(struct ctl_table *table, int write,
 		.mode = table->mode,
 	};
 
+	mutex_lock(&ipvs->sync_mutex);
 	memcpy(val, valp, sizeof(val));
 	rc = proc_dointvec(&tmp, write, buffer, lenp, ppos);
 	if (write) {
@@ -1894,6 +1896,7 @@ proc_do_sync_threshold(struct ctl_table *table, int write,
 		else
 			memcpy(valp, val, sizeof(val));
 	}
+	mutex_unlock(&ipvs->sync_mutex);
 	return rc;
 }
 
@@ -4321,6 +4324,7 @@ static int __net_init ip_vs_control_net_init_sysctl(struct netns_ipvs *ipvs)
 	ipvs->sysctl_sync_threshold[0] = DEFAULT_SYNC_THRESHOLD;
 	ipvs->sysctl_sync_threshold[1] = DEFAULT_SYNC_PERIOD;
 	tbl[idx].data = &ipvs->sysctl_sync_threshold;
+	tbl[idx].extra2 = ipvs;
 	tbl[idx++].maxlen = sizeof(ipvs->sysctl_sync_threshold);
 	ipvs->sysctl_sync_refresh_period = DEFAULT_SYNC_REFRESH_PERIOD;
 	tbl[idx++].data = &ipvs->sysctl_sync_refresh_period;
-- 
2.39.2 (Apple Git-143)