ipvs: Improve robustness to the ipvs sysctl

The ipvs module parse the user buffer and save it to sysctl,
then check if the value is valid. invalid value occurs
over a period of time.
Here, I add a variable, struct ctl_table tmp, used to read
the value from the user buffer, and save only when it is valid.
I delete proc_do_sync_mode and use extra1/2 in table for the
proc_dointvec_minmax call.

Fixes: f73181c8 ("ipvs: add support for sync threads")
Signed-off-by: Junwei Hu <hujunwei4@huawei.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/ipvs/ip_vs_ctl.c

@@ -1737,12 +1737,18 @@ proc_do_defense_mode(struct ctl_table *table, int write,
 	int val = *valp;
 	int rc;
 
-	rc = proc_dointvec(table, write, buffer, lenp, ppos);
+	struct ctl_table tmp = {
+		.data = &val,
+		.maxlen = sizeof(int),
+		.mode = table->mode,
+	};
+
+	rc = proc_dointvec(&tmp, write, buffer, lenp, ppos);
 	if (write && (*valp != val)) {
-		if ((*valp < 0) || (*valp > 3)) {
-			/* Restore the correct value */
-			*valp = val;
+		if (val < 0 || val > 3) {
+			rc = -EINVAL;
 		} else {
+			*valp = val;
 			update_defense_level(ipvs);
 		}
 	}
@@ -1756,37 +1762,24 @@ proc_do_sync_threshold(struct ctl_table *table, int write,
 	int *valp = table->data;
 	int val[2];
 	int rc;
+	struct ctl_table tmp = {
+		.data = &val,
+		.maxlen = table->maxlen,
+		.mode = table->mode,
+	};
 
-	/* backup the value first */
 	memcpy(val, valp, sizeof(val));
-
-	rc = proc_dointvec(table, write, buffer, lenp, ppos);
-	if (write && (valp[0] < 0 || valp[1] < 0 ||
-	    (valp[0] >= valp[1] && valp[1]))) {
-		/* Restore the correct value */
+	rc = proc_dointvec(&tmp, write, buffer, lenp, ppos);
+	if (write) {
+		if (val[0] < 0 || val[1] < 0 ||
+		    (val[0] >= val[1] && val[1]))
+			rc = -EINVAL;
+		else
 			memcpy(valp, val, sizeof(val));
 	}
 	return rc;
 }
 
-static int
-proc_do_sync_mode(struct ctl_table *table, int write,
-		     void __user *buffer, size_t *lenp, loff_t *ppos)
-{
-	int *valp = table->data;
-	int val = *valp;
-	int rc;
-
-	rc = proc_dointvec(table, write, buffer, lenp, ppos);
-	if (write && (*valp != val)) {
-		if ((*valp < 0) || (*valp > 1)) {
-			/* Restore the correct value */
-			*valp = val;
-		}
-	}
-	return rc;
-}
-
 static int
 proc_do_sync_ports(struct ctl_table *table, int write,
 		   void __user *buffer, size_t *lenp, loff_t *ppos)
@@ -1795,13 +1788,19 @@ proc_do_sync_ports(struct ctl_table *table, int write,
 	int val = *valp;
 	int rc;
 
-	rc = proc_dointvec(table, write, buffer, lenp, ppos);
+	struct ctl_table tmp = {
+		.data = &val,
+		.maxlen = sizeof(int),
+		.mode = table->mode,
+	};
+
+	rc = proc_dointvec(&tmp, write, buffer, lenp, ppos);
 	if (write && (*valp != val)) {
-		if (*valp < 1 || !is_power_of_2(*valp)) {
-			/* Restore the correct value */
+		if (val < 1 || !is_power_of_2(val))
+			rc = -EINVAL;
+		else
 			*valp = val;
 	}
-	}
 	return rc;
 }
 
@@ -1860,7 +1859,9 @@ static struct ctl_table vs_vars[] = {
 		.procname	= "sync_version",
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_do_sync_mode,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
 	},
 	{
 		.procname	= "sync_ports",