netdev - [PATCH v2 net-next 6/6] arp: Convert ioctl(SIOCGARP) to RCU.

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Message-ID: <20240425170002.68160-7-kuniyu@amazon.com>
Date: Thu, 25 Apr 2024 10:00:02 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>
CC: Kuniyuki Iwashima <kuniyu@...zon.com>, Kuniyuki Iwashima
	<kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v2 net-next 6/6] arp: Convert ioctl(SIOCGARP) to RCU.

ioctl(SIOCGARP) holds rtnl_lock() for __dev_get_by_name() and
later calls neigh_lookup(), which calls rcu_read_lock().

Let's replace __dev_get_by_name() with dev_get_by_name_rcu() to
avoid locking rtnl_lock().

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv4/arp.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 5034920be85a..9430b64558cd 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1003,11 +1003,15 @@ static int arp_rcv(struct sk_buff *skb, struct net_device *dev,
  *	User level interface (ioctl)
  */
 
-static struct net_device *arp_req_dev_by_name(struct net *net, struct arpreq *r)
+static struct net_device *arp_req_dev_by_name(struct net *net, struct arpreq *r,
+					      bool getarp)
 {
 	struct net_device *dev;
 
-	dev = __dev_get_by_name(net, r->arp_dev);
+	if (getarp)
+		dev = dev_get_by_name_rcu(net, r->arp_dev);
+	else
+		dev = __dev_get_by_name(net, r->arp_dev);
 	if (!dev)
 		return ERR_PTR(-ENODEV);
 
@@ -1028,7 +1032,7 @@ static struct net_device *arp_req_dev(struct net *net, struct arpreq *r)
 	__be32 ip;
 
 	if (r->arp_dev[0])
-		return arp_req_dev_by_name(net, r);
+		return arp_req_dev_by_name(net, r, false);
 
 	if (r->arp_flags & ATF_PUBL)
 		return NULL;
@@ -1166,7 +1170,7 @@ static int arp_req_get(struct net *net, struct arpreq *r)
 	if (!r->arp_dev[0])
 		return -ENODEV;
 
-	dev = arp_req_dev_by_name(net, r);
+	dev = arp_req_dev_by_name(net, r, true);
 	if (IS_ERR(dev))
 		return PTR_ERR(dev);
 
@@ -1287,23 +1291,27 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
 	else if (*netmask && *netmask != htonl(0xFFFFFFFFUL))
 		return -EINVAL;
 
-	rtnl_lock();
-
 	switch (cmd) {
 	case SIOCDARP:
+		rtnl_lock();
 		err = arp_req_delete(net, &r);
+		rtnl_unlock();
 		break;
 	case SIOCSARP:
+		rtnl_lock();
 		err = arp_req_set(net, &r);
+		rtnl_unlock();
 		break;
 	case SIOCGARP:
+		rcu_read_lock();
 		err = arp_req_get(net, &r);
+		rcu_read_unlock();
+
+		if (!err && copy_to_user(arg, &r, sizeof(r)))
+			err = -EFAULT;
 		break;
 	}
 
-	rtnl_unlock();
-	if (cmd == SIOCGARP && !err && copy_to_user(arg, &r, sizeof(r)))
-		err = -EFAULT;
 	return err;
 }
 
-- 
2.30.2