[ATM]: Oops reading net/atm/arp

cat /proc/net/atm/arp causes the NULL pointer dereference in the
get_proc_net+0xc/0x3a. This happens as proc_get_net believes that the
parent proc dir entry contains struct net.

Fix this assumption for "net/atm" case.

The problem is introduced by the commit c0097b07abf5f92ab135d024dd41bd2aada1512f
from Eric W. Biederman/Daniel Lezcano.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/proc/proc_net.c

@@ -96,6 +96,17 @@ static struct proc_dir_entry *proc_net_shadow(struct task_struct *task,
 	return task->nsproxy->net_ns->proc_net;
 }
 
+struct proc_dir_entry *proc_net_mkdir(struct net *net, const char *name,
+		struct proc_dir_entry *parent)
+{
+	struct proc_dir_entry *pde;
+	pde = proc_mkdir_mode(name, S_IRUGO | S_IXUGO, parent);
+	if (pde != NULL)
+		pde->data = net;
+	return pde;
+}
+EXPORT_SYMBOL_GPL(proc_net_mkdir);
+
 static __net_init int proc_net_ns_init(struct net *net)
 {
 	struct proc_dir_entry *root, *netd, *net_statd;
@@ -107,18 +118,16 @@ static __net_init int proc_net_ns_init(struct net *net)
 		goto out;
 
 	err = -EEXIST;
-	netd = proc_mkdir("net", root);
+	netd = proc_net_mkdir(net, "net", root);
 	if (!netd)
 		goto free_root;
 
 	err = -EEXIST;
-	net_statd = proc_mkdir("stat", netd);
+	net_statd = proc_net_mkdir(net, "stat", netd);
 	if (!net_statd)
 		goto free_net;
 
 	root->data = net;
-	netd->data = net;
-	net_statd->data = net;
 
 	net->proc_net_root = root;
 	net->proc_net = netd;

include/linux/proc_fs.h

@@ -201,6 +201,8 @@ static inline struct proc_dir_entry *create_proc_info_entry(const char *name,
 extern struct proc_dir_entry *proc_net_fops_create(struct net *net,
 	const char *name, mode_t mode, const struct file_operations *fops);
 extern void proc_net_remove(struct net *net, const char *name);
+extern struct proc_dir_entry *proc_net_mkdir(struct net *net, const char *name,
+	struct proc_dir_entry *parent);
 
 #else
 

net/atm/proc.c

@@ -476,15 +476,15 @@ static void atm_proc_dirs_remove(void)
 		if (e->dirent)
 			remove_proc_entry(e->name, atm_proc_root);
 	}
-	remove_proc_entry("atm", init_net.proc_net);
+	proc_net_remove(&init_net, "atm");
 }
 
 int __init atm_proc_init(void)
 {
 	static struct atm_proc_entry *e;
 	int ret;
 
-	atm_proc_root = proc_mkdir("atm", init_net.proc_net);
+	atm_proc_root = proc_net_mkdir(&init_net, "atm", init_net.proc_net);
 	if (!atm_proc_root)
 		goto err_out;
 	for (e = atm_proc_ents; e->name; e++) {