net: RCU conversion of dev_getbyhwaddr() and arp_ioctl()

Le dimanche 05 décembre 2010 à 09:19 +0100, Eric Dumazet a écrit :

> Hmm..
>
> If somebody can explain why RTNL is held in arp_ioctl() (and therefore
> in arp_req_delete()), we might first remove RTNL use in arp_ioctl() so
> that your patch can be applied.
>
> Right now it is not good, because RTNL wont be necessarly held when you
> are going to call arp_invalidate() ?

While doing this analysis, I found a refcount bug in llc, I'll send a
patch for net-2.6

Meanwhile, here is the patch for net-next-2.6

Your patch then can be applied after mine.

Thanks

[PATCH] net: RCU conversion of dev_getbyhwaddr() and arp_ioctl()

dev_getbyhwaddr() was called under RTNL.

Rename it to dev_getbyhwaddr_rcu() and change all its caller to now use
RCU locking instead of RTNL.

Change arp_ioctl() to use RCU instead of RTNL locking.

Note: this fix a dev refcount bug in llc

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 8 deletions

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 10af759f2630..a2fc7b961dbc 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1017,13 +1017,14 @@ static int arp_req_set_proxy(struct net *net, struct net_device *dev, int on)
                 IPV4_DEVCONF_ALL(net, PROXY_ARP) = on;
                 return 0;
         }
-        if (__in_dev_get_rtnl(dev)) {
-                IN_DEV_CONF_SET(__in_dev_get_rtnl(dev), PROXY_ARP, on);
+        if (__in_dev_get_rcu(dev)) {
+                IN_DEV_CONF_SET(__in_dev_get_rcu(dev), PROXY_ARP, on);
                 return 0;
         }
         return -ENXIO;
 }
 
+/* must be called with rcu_read_lock() */
 static int arp_req_set_public(struct net *net, struct arpreq *r,
                 struct net_device *dev)
 {
@@ -1033,7 +1034,7 @@ static int arp_req_set_public(struct net *net, struct arpreq *r,
         if (mask && mask != htonl(0xFFFFFFFF))
                 return -EINVAL;
         if (!dev && (r->arp_flags & ATF_COM)) {
-                dev = dev_getbyhwaddr(net, r->arp_ha.sa_family,
+                dev = dev_getbyhwaddr_rcu(net, r->arp_ha.sa_family,
                                       r->arp_ha.sa_data);
                 if (!dev)
                         return -ENODEV;
@@ -1225,10 +1226,10 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
         if (!(r.arp_flags & ATF_NETMASK))
                 ((struct sockaddr_in *)&r.arp_netmask)->sin_addr.s_addr =
                                                            htonl(0xFFFFFFFFUL);
-        rtnl_lock();
+        rcu_read_lock();
         if (r.arp_dev[0]) {
                 err = -ENODEV;
-                dev = __dev_get_by_name(net, r.arp_dev);
+                dev = dev_get_by_name_rcu(net, r.arp_dev);
                 if (dev == NULL)
                         goto out;
 
@@ -1252,12 +1253,12 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
                 break;
         case SIOCGARP:
                 err = arp_req_get(&r, dev);
-                if (!err && copy_to_user(arg, &r, sizeof(r)))
-                        err = -EFAULT;
                 break;
         }
 out:
-        rtnl_unlock();
+        rcu_read_unlock();
+        if (cmd == SIOCGARP && !err && copy_to_user(arg, &r, sizeof(r)))
+                err = -EFAULT;
         return err;
 }