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net: fix dev_seq_next()

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Commit c6d14c8456 (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: Eric Dumazet <eric.dumazet@gmail.com>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2011-01-26 18:08:02 +00:00 committed by David S. Miller
parent 065825402c
commit ccf434380d
2 changed files with 15 additions and 5 deletions
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9
include/linux/netdevice.h
View file

@ -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,

11
net/core/dev.c
View file

@ -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)