[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>

3 files changed, 17 insertions, 6 deletions

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index cfc4f6c072f1..4823c9677fac 100644
--- a/fs/proc/proc_net.c
+++ b/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;
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index a5316829215b..8f92546b403d 100644
--- a/include/linux/proc_fs.h
+++ b/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
 
diff --git a/net/atm/proc.c b/net/atm/proc.c
index 5d9d5ffba145..565e75e62ca4 100644
--- a/net/atm/proc.c
+++ b/net/atm/proc.c
@@ -476,7 +476,7 @@ 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)
@@ -484,7 +484,7 @@ 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++) {