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 --- net/netlink/af_netlink.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'net/netlink') diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 3029f865cd6..dc9f8c2ab1d 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -1859,7 +1859,11 @@ static int netlink_seq_open(struct inode *inode, struct file *file) seq = file->private_data; seq->private = iter; - iter->net = get_net(PROC_NET(inode)); + iter->net = get_proc_net(inode); + if (!iter->net) { + seq_release_private(inode, file); + return -ENXIO; + } return 0; } -- cgit v1.2.3