net: Protect dev->name by seqlock.

We will convert ioctl(SIOCGARP) to RCU, and then we need to copy
dev->name which is currently protected by rtnl_lock().

This patch does the following:

  1) Add seqlock netdev_rename_lock to protect dev->name

  2) Add netdev_copy_name() that copies dev->name to buffer
     under netdev_rename_lock

  3) Use netdev_copy_name() in netdev_get_name() and drop
     devnet_rename_sem

Suggested-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/CANn89iJEWs7AYSJqGCUABeVqOCTkErponfZdT5kV-iD=-SajnQ@mail.gmail.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240430015813.71143-7-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f849e7d110ed9618078c49b7871070118edc5a5c..41853424b41d7a95e896e2f62318c161468c2437 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3136,6 +3136,7 @@ struct net_device *netdev_get_by_name(struct net *net, const char *name,
                                      netdevice_tracker *tracker, gfp_t gfp);
 struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex);
 struct net_device *dev_get_by_napi_id(unsigned int napi_id);
+void netdev_copy_name(struct net_device *dev, char *name);
 
 static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,
                                  unsigned short type,

diff --git a/net/core/dev.c b/net/core/dev.c
index cd7ba50eac15341c1d3a2136f8b4a3584d5c2669..e02d2363347e2e403ccb2a59d44d35cee9a1b367 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -940,6 +940,18 @@ struct net_device *dev_get_by_napi_id(unsigned int napi_id)
 }
 EXPORT_SYMBOL(dev_get_by_napi_id);
 
+static DEFINE_SEQLOCK(netdev_rename_lock);
+
+void netdev_copy_name(struct net_device *dev, char *name)
+{
+       unsigned int seq;
+
+       do {
+               seq = read_seqbegin(&netdev_rename_lock);
+               strscpy(name, dev->name, IFNAMSIZ);
+       } while (read_seqretry(&netdev_rename_lock, seq));
+}
+
 /**
  *     netdev_get_name - get a netdevice name, knowing its ifindex.
  *     @net: network namespace
@@ -951,7 +963,6 @@ int netdev_get_name(struct net *net, char *name, int ifindex)
        struct net_device *dev;
        int ret;
 
-       down_read(&devnet_rename_sem);
        rcu_read_lock();
 
        dev = dev_get_by_index_rcu(net, ifindex);
@@ -960,12 +971,11 @@ int netdev_get_name(struct net *net, char *name, int ifindex)
                goto out;
        }
 
-       strcpy(name, dev->name);
+       netdev_copy_name(dev, name);
 
        ret = 0;
 out:
        rcu_read_unlock();
-       up_read(&devnet_rename_sem);
        return ret;
 }
 
@@ -1217,7 +1227,10 @@ int dev_change_name(struct net_device *dev, const char *newname)
 
        memcpy(oldname, dev->name, IFNAMSIZ);
 
+       write_seqlock(&netdev_rename_lock);
        err = dev_get_valid_name(net, dev, newname);
+       write_sequnlock(&netdev_rename_lock);
+
        if (err < 0) {
                up_write(&devnet_rename_sem);
                return err;
@@ -1257,7 +1270,9 @@ rollback:
                if (err >= 0) {
                        err = ret;
                        down_write(&devnet_rename_sem);
+                       write_seqlock(&netdev_rename_lock);
                        memcpy(dev->name, oldname, IFNAMSIZ);
+                       write_sequnlock(&netdev_rename_lock);
                        memcpy(oldname, newname, IFNAMSIZ);
                        WRITE_ONCE(dev->name_assign_type, old_assign_type);
                        old_assign_type = NET_NAME_RENAMED;
@@ -11403,8 +11418,12 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
        dev_net_set(dev, net);
        dev->ifindex = new_ifindex;
 
-       if (new_name[0]) /* Rename the netdev to prepared name */
+       if (new_name[0]) {
+               /* Rename the netdev to prepared name */
+               write_seqlock(&netdev_rename_lock);
                strscpy(dev->name, new_name, IFNAMSIZ);
+               write_sequnlock(&netdev_rename_lock);
+       }
 
        /* Fixup kobjects */
        dev_set_uevent_suppress(&dev->dev, 1);