[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>

4 files changed, 114 insertions, 37 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 96ee899d6502..cc43cf0c1fa5 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2274,6 +2274,7 @@ static const struct pid_entry tgid_base_stuff[] = {
         DIR("task",       S_IRUGO|S_IXUGO, task),
         DIR("fd",         S_IRUSR|S_IXUSR, fd),
         DIR("fdinfo",     S_IRUSR|S_IXUSR, fdinfo),
+        DIR("net",        S_IRUGO|S_IXUSR, net),
         REG("environ",    S_IRUSR, environ),
         INF("auxv",       S_IRUSR, pid_auxv),
         ONE("status",     S_IRUGO, pid_status),
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 68971e66cd41..a36ad3c75cf4 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -377,15 +377,14 @@ static struct dentry_operations proc_dentry_operations =
  * Don't create negative dentries here, return -ENOENT by hand
  * instead.
  */
-struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nameidata *nd)
+struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *dir,
+                struct dentry *dentry)
 {
         struct inode *inode = NULL;
-        struct proc_dir_entry * de;
         int error = -ENOENT;
 
         lock_kernel();
         spin_lock(&proc_subdir_lock);
-        de = PDE(dir);
         if (de) {
                 for (de = de->subdir; de ; de = de->next) {
                         if (de->namelen != dentry->d_name.len)
@@ -393,8 +392,6 @@ struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nam
                         if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
                                 unsigned int ino;
 
-                                if (de->shadow_proc)
-                                        de = de->shadow_proc(current, de);
                                 ino = de->low_ino;
                                 de_get(de);
                                 spin_unlock(&proc_subdir_lock);
@@ -417,6 +414,12 @@ out_unlock:
         return ERR_PTR(error);
 }
 
+struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
+                struct nameidata *nd)
+{
+        return proc_lookup_de(PDE(dir), dir, dentry);
+}
+
 /*
  * This returns non-zero if at EOF, so that the /proc
  * root directory can use this and check if it should
@@ -426,10 +429,9 @@ out_unlock:
  * value of the readdir() call, as long as it's non-negative
  * for success..
  */
-int proc_readdir(struct file * filp,
-        void * dirent, filldir_t filldir)
+int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent,
+                filldir_t filldir)
 {
-        struct proc_dir_entry * de;
         unsigned int ino;
         int i;
         struct inode *inode = filp->f_path.dentry->d_inode;
@@ -438,7 +440,6 @@ int proc_readdir(struct file * filp,
         lock_kernel();
 
         ino = inode->i_ino;
-        de = PDE(inode);
         if (!de) {
                 ret = -EINVAL;
                 goto out;
@@ -499,6 +500,13 @@ out:	unlock_kernel();
         return ret;     
 }
 
+int proc_readdir(struct file *filp, void *dirent, filldir_t filldir)
+{
+        struct inode *inode = filp->f_path.dentry->d_inode;
+
+        return proc_readdir_de(PDE(inode), filp, dirent, filldir);
+}
+
 /*
  * These are the generic /proc directory operations. They
  * use the in-memory "struct proc_dir_entry" tree to parse
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 1c81c8f1aeed..bc72f5c8c47d 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -64,6 +64,8 @@ extern const struct file_operations proc_numa_maps_operations;
 extern const struct file_operations proc_smaps_operations;
 extern const struct file_operations proc_clear_refs_operations;
 extern const struct file_operations proc_pagemap_operations;
+extern const struct file_operations proc_net_operations;
+extern const struct inode_operations proc_net_inode_operations;
 
 void free_proc_entry(struct proc_dir_entry *de);
 
@@ -83,3 +85,8 @@ static inline int proc_fd(struct inode *inode)
 {
         return PROC_I(inode)->fd;
 }
+
+struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *ino,
+                struct dentry *dentry);
+int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent,
+                filldir_t filldir);
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 14e9b5aaf863..4caa5f774fb7 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -63,6 +63,82 @@ int seq_release_net(struct inode *ino, struct file *f)
 }
 EXPORT_SYMBOL_GPL(seq_release_net);
 
+static struct net *get_proc_task_net(struct inode *dir)
+{
+        struct task_struct *task;
+        struct nsproxy *ns;
+        struct net *net = NULL;
+
+        rcu_read_lock();
+        task = pid_task(proc_pid(dir), PIDTYPE_PID);
+        if (task != NULL) {
+                ns = task_nsproxy(task);
+                if (ns != NULL)
+                        net = get_net(ns->net_ns);
+        }
+        rcu_read_unlock();
+
+        return net;
+}
+
+static struct dentry *proc_tgid_net_lookup(struct inode *dir,
+                struct dentry *dentry, struct nameidata *nd)
+{
+        struct dentry *de;
+        struct net *net;
+
+        de = ERR_PTR(-ENOENT);
+        net = get_proc_task_net(dir);
+        if (net != NULL) {
+                de = proc_lookup_de(net->proc_net, dir, dentry);
+                put_net(net);
+        }
+        return de;
+}
+
+static int proc_tgid_net_getattr(struct vfsmount *mnt, struct dentry *dentry,
+                struct kstat *stat)
+{
+        struct inode *inode = dentry->d_inode;
+        struct net *net;
+
+        net = get_proc_task_net(inode);
+
+        generic_fillattr(inode, stat);
+
+        if (net != NULL) {
+                stat->nlink = net->proc_net->nlink;
+                put_net(net);
+        }
+
+        return 0;
+}
+
+const struct inode_operations proc_net_inode_operations = {
+        .lookup         = proc_tgid_net_lookup,
+        .getattr        = proc_tgid_net_getattr,
+};
+
+static int proc_tgid_net_readdir(struct file *filp, void *dirent,
+                filldir_t filldir)
+{
+        int ret;
+        struct net *net;
+
+        ret = -EINVAL;
+        net = get_proc_task_net(filp->f_path.dentry->d_inode);
+        if (net != NULL) {
+                ret = proc_readdir_de(net->proc_net, filp, dirent, filldir);
+                put_net(net);
+        }
+        return ret;
+}
+
+const struct file_operations proc_net_operations = {
+        .read           = generic_read_dir,
+        .readdir        = proc_tgid_net_readdir,
+};
+
 
 struct proc_dir_entry *proc_net_fops_create(struct net *net,
         const char *name, mode_t mode, const struct file_operations *fops)
@@ -83,14 +159,6 @@ struct net *get_proc_net(const struct inode *inode)
 }
 EXPORT_SYMBOL_GPL(get_proc_net);
 
-static struct proc_dir_entry *shadow_pde;
-
-static struct proc_dir_entry *proc_net_shadow(struct task_struct *task,
-                                                struct proc_dir_entry *de)
-{
-        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)
 {
@@ -104,45 +172,39 @@ 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;
+        struct proc_dir_entry *netd, *net_statd;
         int err;
 
         err = -ENOMEM;
-        root = kzalloc(sizeof(*root), GFP_KERNEL);
-        if (!root)
+        netd = kzalloc(sizeof(*netd), GFP_KERNEL);
+        if (!netd)
                 goto out;
 
-        err = -EEXIST;
-        netd = proc_net_mkdir(net, "net", root);
-        if (!netd)
-                goto free_root;
+        netd->data = net;
+        netd->nlink = 2;
+        netd->name = "net";
+        netd->namelen = 3;
+        netd->parent = &proc_root;
 
         err = -EEXIST;
         net_statd = proc_net_mkdir(net, "stat", netd);
         if (!net_statd)
                 goto free_net;
 
-        root->data = net;
-
-        net->proc_net_root = root;
         net->proc_net = netd;
         net->proc_net_stat = net_statd;
-        err = 0;
+        return 0;
 
+free_net:
+        kfree(netd);
 out:
         return err;
-free_net:
-        remove_proc_entry("net", root);
-free_root:
-        kfree(root);
-        goto out;
 }
 
 static __net_exit void proc_net_ns_exit(struct net *net)
 {
         remove_proc_entry("stat", net->proc_net);
-        remove_proc_entry("net", net->proc_net_root);
-        kfree(net->proc_net_root);
+        kfree(net->proc_net);
 }
 
 static struct pernet_operations __net_initdata proc_net_ns_ops = {
@@ -152,8 +214,7 @@ static struct pernet_operations __net_initdata proc_net_ns_ops = {
 
 int __init proc_net_init(void)
 {
-        shadow_pde = proc_mkdir("net", NULL);
-        shadow_pde->shadow_proc = proc_net_shadow;
+        proc_symlink("net", NULL, "self/net");
 
         return register_pernet_subsys(&proc_net_ns_ops);
 }