net: fix dev_ifsioc_locked() race condition

dev_ifsioc_locked() is called with only RCU read lock, so when
there is a parallel writer changing the mac address, it could
get a partially updated mac address, as shown below:

Thread 1			Thread 2
// eth_commit_mac_addr_change()
memcpy(dev->dev_addr, addr->sa_data, ETH_ALEN);
				// dev_ifsioc_locked()
				memcpy(ifr->ifr_hwaddr.sa_data,
					dev->dev_addr,...);

Close this race condition by guarding them with a RW semaphore,
like netdev_get_name(). We can not use seqlock here as it does not
allow blocking. The writers already take RTNL anyway, so this does
not affect the slow path. To avoid bothering existing
dev_set_mac_address() callers in drivers, introduce a new wrapper
just for user-facing callers on ioctl and rtnetlink paths.

Note, bonding also changes slave mac addresses but that requires
a separate patch due to the complexity of bonding code.

Fixes: 3710becf8a58 ("net: RCU locking for simple ioctl()")
Reported-by: "Gong, Sishuai" <sishuai@purdue.edu>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 50 insertions, 14 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 321d41a110e7..ce6291bc2e16 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8937,6 +8937,48 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 }
 EXPORT_SYMBOL(dev_set_mac_address);
 
+static DECLARE_RWSEM(dev_addr_sem);
+
+int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
+			     struct netlink_ext_ack *extack)
+{
+	int ret;
+
+	down_write(&dev_addr_sem);
+	ret = dev_set_mac_address(dev, sa, extack);
+	up_write(&dev_addr_sem);
+	return ret;
+}
+EXPORT_SYMBOL(dev_set_mac_address_user);
+
+int dev_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name)
+{
+	size_t size = sizeof(sa->sa_data);
+	struct net_device *dev;
+	int ret = 0;
+
+	down_read(&dev_addr_sem);
+	rcu_read_lock();
+
+	dev = dev_get_by_name_rcu(net, dev_name);
+	if (!dev) {
+		ret = -ENODEV;
+		goto unlock;
+	}
+	if (!dev->addr_len)
+		memset(sa->sa_data, 0, size);
+	else
+		memcpy(sa->sa_data, dev->dev_addr,
+		       min_t(size_t, size, dev->addr_len));
+	sa->sa_family = dev->type;
+
+unlock:
+	rcu_read_unlock();
+	up_read(&dev_addr_sem);
+	return ret;
+}
+EXPORT_SYMBOL(dev_get_mac_address);
+
 /**
  *	dev_change_carrier - Change device carrier
  *	@dev: device
diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index db8a0ff86f36..478d032f34ac 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -123,17 +123,6 @@ static int dev_ifsioc_locked(struct net *net, struct ifreq *ifr, unsigned int cm
 		ifr->ifr_mtu = dev->mtu;
 		return 0;
 
-	case SIOCGIFHWADDR:
-		if (!dev->addr_len)
-			memset(ifr->ifr_hwaddr.sa_data, 0,
-			       sizeof(ifr->ifr_hwaddr.sa_data));
-		else
-			memcpy(ifr->ifr_hwaddr.sa_data, dev->dev_addr,
-			       min(sizeof(ifr->ifr_hwaddr.sa_data),
-				   (size_t)dev->addr_len));
-		ifr->ifr_hwaddr.sa_family = dev->type;
-		return 0;
-
 	case SIOCGIFSLAVE:
 		err = -EINVAL;
 		break;
@@ -274,7 +263,7 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
 	case SIOCSIFHWADDR:
 		if (dev->addr_len > sizeof(struct sockaddr))
 			return -EINVAL;
-		return dev_set_mac_address(dev, &ifr->ifr_hwaddr, NULL);
+		return dev_set_mac_address_user(dev, &ifr->ifr_hwaddr, NULL);
 
 	case SIOCSIFHWBROADCAST:
 		if (ifr->ifr_hwaddr.sa_family != dev->type)
@@ -418,6 +407,12 @@ int dev_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr, bool *need_c
 	 */
 
 	switch (cmd) {
+	case SIOCGIFHWADDR:
+		dev_load(net, ifr->ifr_name);
+		ret = dev_get_mac_address(&ifr->ifr_hwaddr, net, ifr->ifr_name);
+		if (colon)
+			*colon = ':';
+		return ret;
 	/*
 	 *	These ioctl calls:
 	 *	- can be done by all.
@@ -427,7 +422,6 @@ int dev_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr, bool *need_c
 	case SIOCGIFFLAGS:
 	case SIOCGIFMETRIC:
 	case SIOCGIFMTU:
-	case SIOCGIFHWADDR:
 	case SIOCGIFSLAVE:
 	case SIOCGIFMAP:
 	case SIOCGIFINDEX:
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c313aaf2bce1..0edc0b2baaa4 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2660,7 +2660,7 @@ static int do_setlink(const struct sk_buff *skb,
 		sa->sa_family = dev->type;
 		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
 		       dev->addr_len);
-		err = dev_set_mac_address(dev, sa, extack);
+		err = dev_set_mac_address_user(dev, sa, extack);
 		kfree(sa);
 		if (err)
 			goto errout;