[NET]: Make /proc/net a symlink on /proc/self/net (v3)

Current /proc/net is done with so called "shadows", but current
implementation is broken and has little chances to get fixed.

The problem is that dentries subtree of /proc/net directory has
fancy revalidation rules to make processes living in different
net namespaces see different entries in /proc/net subtree, but
currently, tasks see in the /proc/net subdir the contents of any
other namespace, depending on who opened the file first.

The proposed fix is to turn /proc/net into a symlink, which points
to /proc/self/net, which in turn shows what previously was in
/proc/net - the network-related info, from the net namespace the
appropriate task lives in.

# ls -l /proc/net
lrwxrwxrwx  1 root root 8 Mar  5 15:17 /proc/net -> self/net

In other words - this behaves like /proc/mounts, but unlike
"mounts", "net" is not a file, but a directory.

Changes from v2:
* Fixed discrepancy of /proc/net nlink count and selinux labeling
  screwup pointed out by Stephen.

  To get the correct nlink count the ->getattr callback for /proc/net
  is overridden to read one from the net->proc_net entry.

  To make selinux still work the net->proc_net entry is initialized
  properly, i.e. with the "net" name and the proc_net parent.

Selinux fixes are
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>

Changes from v1:
* Fixed a task_struct leak in get_proc_task_net, pointed out by Paul.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 3 deletions

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index d9a9e718ad19..9b6c935f69cf 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -50,8 +50,6 @@ typedef	int (read_proc_t)(char *page, char **start, off_t off,
 typedef int (write_proc_t)(struct file *file, const char __user *buffer,
                            unsigned long count, void *data);
 typedef int (get_info_t)(char *, char **, off_t, int);
-typedef struct proc_dir_entry *(shadow_proc_t)(struct task_struct *task,
-                                                struct proc_dir_entry *pde);
 
 struct proc_dir_entry {
         unsigned int low_ino;
@@ -82,7 +80,6 @@ struct proc_dir_entry {
         int pde_users;  /* number of callers into module in progress */
         spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
         struct completion *pde_unload_completion;
-        shadow_proc_t *shadow_proc;
 };
 
 struct kcore_list {