[PATCH] ipvs: fix racy memcpy in proc_do_sync_threshold

[Sishuai Gong <sishuai.system@xxxxxxxxx>]

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 <sishuai.system@xxxxxxxxx>
---
 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)