From 077130c0cf7d5ba1992f5b51b96136d7b1c8aad5 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Thu, 13 Sep 2007 09:18:57 +0200 Subject: [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 Acked-by: Paul E. McKenney Signed-off-by: David S. Miller --- include/net/net_namespace.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'include/net') diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index 3081b6ed35f..ac8f8304094 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) 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)) -- cgit v1.2.3