[PPPOE]: race between interface going down and connect()

below you find a patch that (hopefully) fixes a race between an interface
going down and a connect() to a peer on that interface. Before,
connect() would determine that an interface is up, then the interface
could go down and all entries referring to that interface in the
item_hash_table would be marked as ZOMBIEs and their references to
the device would be freed, and after that, connect() would put a new
entry into the hash table referring to the device that meanwhile is
down already - which also would cause unregister_netdevice() to wait
until the socket has been release()d.

This patch does not suffice if we are not allowed to accept connect()s
referring to a device that we already acked a NETDEV_GOING_DOWN for
(that is: all references are only guaranteed to be freed after
NETDEV_DOWN has been acknowledged, not necessarily after the
NETDEV_GOING_DOWN already). And if we are allowed to, we could avoid
looking through the hash table upon NETDEV_GOING_DOWN completely and
only do that once we get the NETDEV_DOWN ...

mostrows:
pppoe_flush_dev is called on NETDEV_GOING_DOWN and NETDEV_DOWN to deal with
this "late connect" issue.  Ideally one would hope to notify users at the
"NETDEV_GOING_DOWN" phase (just to pretend to be nice).  However, it is the
NETDEV_DOWN scan that takes all the responsibility for ensuring nobody is
hanging around at that time.

Signed-off-by: Florian Zumbiehl <florz@florz.de>
Acked-by: Michal Ostrowski <mostrows@earthlink.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/pppoe.c b/drivers/net/pppoe.c
index f761a9aae4c81fc10dd17852275c2c68c0036223..bc4fc30bc85ec3ca38044b02f63af016156e2be5 100644 (file)
--- a/drivers/net/pppoe.c
+++ b/drivers/net/pppoe.c
@@ -218,17 +218,6 @@ static inline struct pppox_sock *get_item_by_addr(struct sockaddr_pppox *sp)
        return get_item(sp->sa_addr.pppoe.sid, sp->sa_addr.pppoe.remote, ifindex);
 }
 
-static inline int set_item(struct pppox_sock *po)
-{
-       int i;
-
-       write_lock_bh(&pppoe_hash_lock);
-       i = __set_item(po);
-       write_unlock_bh(&pppoe_hash_lock);
-
-       return i;
-}
-
 static inline struct pppox_sock *delete_item(unsigned long sid, char *addr, int ifindex)
 {
        struct pppox_sock *ret;
@@ -595,14 +584,18 @@ static int pppoe_connect(struct socket *sock, struct sockaddr *uservaddr,
                po->pppoe_dev = dev;
                po->pppoe_ifindex = dev->ifindex;
 
-               if (!(dev->flags & IFF_UP))
+               write_lock_bh(&pppoe_hash_lock);
+               if (!(dev->flags & IFF_UP)){
+                       write_unlock_bh(&pppoe_hash_lock);
                        goto err_put;
+               }
 
                memcpy(&po->pppoe_pa,
                       &sp->sa_addr.pppoe,
                       sizeof(struct pppoe_addr));
 
-               error = set_item(po);
+               error = __set_item(po);
+               write_unlock_bh(&pppoe_hash_lock);
                if (error < 0)
                        goto err_put;