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 --- fs/proc/proc_net.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs/proc') diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c index 358930a3142a..85cc8e8bb862 100644 --- a/fs/proc/proc_net.c +++ b/fs/proc/proc_net.c @@ -51,6 +51,12 @@ void proc_net_remove(struct net *net, const char *name) } EXPORT_SYMBOL_GPL(proc_net_remove); +struct net *get_proc_net(const struct inode *inode) +{ + return maybe_get_net(PDE_NET(PDE(inode))); +} +EXPORT_SYMBOL_GPL(get_proc_net); + static struct proc_dir_entry *proc_net_shadow; static struct dentry *proc_net_shadow_dentry(struct dentry *parent, -- cgit v1.2.2