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authorEric W. Biederman <ebiederm@xmission.com>2007-09-13 03:18:57 -0400
committerDavid S. Miller <davem@sunset.davemloft.net>2007-10-10 19:49:22 -0400
commit077130c0cf7d5ba1992f5b51b96136d7b1c8aad5 (patch)
treec8fd2622e7d633cc504c7543b55e25bd6d99a2fa /include/net/net_namespace.h
parent4fabcd7118162e36eea5c53e8895ecc13762bef3 (diff)
[NET]: Fix race when opening a proc file while a network namespace is exiting.
The problem: proc_net files remember which network namespace the are against but do not remember hold a reference count (as that would pin the network namespace). So we currently have a small window where the reference count on a network namespace may be incremented when opening a /proc file when it has already gone to zero. To fix this introduce maybe_get_net and get_proc_net. maybe_get_net increments the network namespace reference count only if it is greater then zero, ensuring we don't increment a reference count after it has gone to zero. get_proc_net handles all of the magic to go from a proc inode to the network namespace instance and call maybe_get_net on it. PROC_NET the old accessor is removed so that we don't get confused and use the wrong helper function. Then I fix up the callers to use get_proc_net and handle the case case where get_proc_net returns NULL. In that case I return -ENXIO because effectively the network namespace has already gone away so the files we are trying to access don't exist anymore. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/net_namespace.h')
-rw-r--r--include/net/net_namespace.h12
1 files changed, 12 insertions, 0 deletions
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 3081b6ed35fe..ac8f8304094e 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -46,6 +46,18 @@ static inline struct net *get_net(struct net *net)
46 return net; 46 return net;
47} 47}
48 48
49static inline struct net *maybe_get_net(struct net *net)
50{
51 /* Used when we know struct net exists but we
52 * aren't guaranteed a previous reference count
53 * exists. If the reference count is zero this
54 * function fails and returns NULL.
55 */
56 if (!atomic_inc_not_zero(&net->count))
57 net = NULL;
58 return net;
59}
60
49static inline void put_net(struct net *net) 61static inline void put_net(struct net *net)
50{ 62{
51 if (atomic_dec_and_test(&net->count)) 63 if (atomic_dec_and_test(&net->count))