[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>
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 3081b6e..ac8f8304 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -46,6 +46,18 @@
return net;
}
+static inline struct net *maybe_get_net(struct net *net)
+{
+ /* Used when we know struct net exists but we
+ * aren't guaranteed a previous reference count
+ * exists. If the reference count is zero this
+ * function fails and returns NULL.
+ */
+ if (!atomic_inc_not_zero(&net->count))
+ net = NULL;
+ return net;
+}
+
static inline void put_net(struct net *net)
{
if (atomic_dec_and_test(&net->count))