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Commit ccf43438 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: fix dev_seq_next() 



Commit c6d14c84 (net: Introduce for_each_netdev_rcu() iterator)
added a race in dev_seq_next().

The rcu_dereference() call should be done _before_ testing the end of
list, or we might return a wrong net_device if a concurrent thread
changes net_device list under us.

Note : discovered thanks to a sparse warning :

net/core/dev.c:3919:9: error: incompatible types in comparison expression
(different address spaces)

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 06582540

include/linux/netdevice.h

+8 −1
Original line number Diff line number Diff line
@@ -1447,7 +1447,7 @@ static inline struct net_device *next_net_device_rcu(struct net_device *dev) 
	struct net *net;



	net = dev_net(dev);

	lh = rcu_dereference(dev->dev_list.next);

	lh = rcu_dereference(list_next_rcu(&dev->dev_list));

	return lh == &net->dev_base_head ? NULL : net_device_entry(lh);

}
@@ -1457,6 +1457,13 @@ static inline struct net_device *first_net_device(struct net *net) 
		net_device_entry(net->dev_base_head.next);

}



static inline struct net_device *first_net_device_rcu(struct net *net)

{

	struct list_head *lh = rcu_dereference(list_next_rcu(&net->dev_base_head));



	return lh == &net->dev_base_head ? NULL : net_device_entry(lh);

}



extern int 			netdev_boot_setup_check(struct net_device *dev);

extern unsigned long		netdev_boot_base(const char *prefix, int unit);

extern struct net_device *dev_getbyhwaddr_rcu(struct net *net, unsigned short type,

net/core/dev.c

+7 −4
Original line number Diff line number Diff line
@@ -4051,12 +4051,15 @@ void *dev_seq_start(struct seq_file *seq, loff_t *pos) 


void *dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)

{

	struct net_device *dev = (v == SEQ_START_TOKEN) ?

				  first_net_device(seq_file_net(seq)) :

				  next_net_device((struct net_device *)v);

	struct net_device *dev = v;



	if (v == SEQ_START_TOKEN)

		dev = first_net_device_rcu(seq_file_net(seq));

	else

		dev = next_net_device_rcu(dev);



	++*pos;

	return rcu_dereference(dev);

	return dev;

}



void dev_seq_stop(struct seq_file *seq, void *v)