[PATCH 4.19 109/129] ipvs: fix racy memcpy in proc_do_sync_threshold

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sishuai Gong <sishuai.system@xxxxxxxxx>

commit 5310760af1d4fbea1452bfc77db5f9a680f7ae47 upstream.

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 serialize them.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/netdev/B6988E90-0A1E-4B85-BF26-2DAF6D482433@xxxxxxxxx/
Signed-off-by: Sishuai Gong <sishuai.system@xxxxxxxxx>
Acked-by: Simon Horman <horms@xxxxxxxxxx>
Acked-by: Julian Anastasov <ja@xxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/netfilter/ipvs/ip_vs_ctl.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -1690,6 +1690,7 @@ static int
 proc_do_sync_threshold(struct ctl_table *table, int write,
 		       void __user *buffer, size_t *lenp, loff_t *ppos)
 {
+	struct netns_ipvs *ipvs = table->extra2;
 	int *valp = table->data;
 	int val[2];
 	int rc;
@@ -1699,6 +1700,7 @@ proc_do_sync_threshold(struct ctl_table
 		.mode = table->mode,
 	};
 
+	mutex_lock(&ipvs->sync_mutex);
 	memcpy(val, valp, sizeof(val));
 	rc = proc_dointvec(&tmp, write, buffer, lenp, ppos);
 	if (write) {
@@ -1708,6 +1710,7 @@ proc_do_sync_threshold(struct ctl_table
 		else
 			memcpy(valp, val, sizeof(val));
 	}
+	mutex_unlock(&ipvs->sync_mutex);
 	return rc;
 }
 
@@ -3944,6 +3947,7 @@ static int __net_init ip_vs_control_net_
 	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;





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