[PATCH v3 net-next 06/13] net-sysfs: use dev_addr_sem to remove races in address_show()

[Eric Dumazet <edumazet@google.com>]

Using dev_base_lock is not preventing from reading garbage.

Use dev_addr_sem instead.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/netdevice.h |  1 +
 net/core/dev.c            |  2 +-
 net/core/net-sysfs.c      | 10 +++++++---
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 24fd24b0f2341f662b28ade45ed12a5e6d02852a..28569f195a449700b6403006f70257b8194b516a 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4031,6 +4031,7 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 			struct netlink_ext_ack *extack);
 int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
 			     struct netlink_ext_ack *extack);
+extern struct rw_semaphore dev_addr_sem;
 int dev_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name);
 int dev_get_port_parent_id(struct net_device *dev,
 			   struct netdev_phys_item_id *ppid, bool recurse);
diff --git a/net/core/dev.c b/net/core/dev.c
index 7d9d43ce2cb779c922759224e2690e24acda77fd..0c158dd534f80c46e66c890628be9a876e85068a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8951,7 +8951,7 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 }
 EXPORT_SYMBOL(dev_set_mac_address);
 
-static DECLARE_RWSEM(dev_addr_sem);
+DECLARE_RWSEM(dev_addr_sem);
 
 int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
 			     struct netlink_ext_ack *extack)
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 678e4be690821c5cdb933f5e91af2247ebecb830..23ef2df549c3036a702f3be1dca1eda14ee5e76f 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -142,17 +142,21 @@ static ssize_t name_assign_type_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(name_assign_type);
 
-/* use same locking rules as GIFHWADDR ioctl's */
+/* use same locking rules as GIFHWADDR ioctl's (dev_get_mac_address()) */
 static ssize_t address_show(struct device *dev, struct device_attribute *attr,
 			    char *buf)
 {
 	struct net_device *ndev = to_net_dev(dev);
 	ssize_t ret = -EINVAL;
 
-	read_lock(&dev_base_lock);
+	down_read(&dev_addr_sem);
+
+	rcu_read_lock();
 	if (dev_isalive(ndev))
 		ret = sysfs_format_mac(buf, ndev->dev_addr, ndev->addr_len);
-	read_unlock(&dev_base_lock);
+	rcu_read_unlock();
+
+	up_read(&dev_addr_sem);
 	return ret;
 }
 static DEVICE_ATTR_RO(address);
-- 
2.43.0.687.g38aa6559b0-goog