[NETNS]: Fix /proc/net breakage

Well I clearly goofed when I added the initial network namespace support
for /proc/net.  Currently things work but there are odd details visible to
user space, even when we have a single network namespace.

Since we do not cache proc_dir_entry dentries at the moment we can just
modify ->lookup to return a different directory inode depending on the
network namespace of the process looking at /proc/net, replacing the
current technique of using a magic and fragile follow_link method.

To accomplish that this patch:
- introduces a shadow_proc method to allow different dentries to
  be returned from proc_lookup.
- Removes the old /proc/net follow_link magic
- Fixes a weakness in our not caching of proc generic dentries.

As shadow_proc uses a task struct to decided which dentry to return we can
go back later and fix the proc generic caching without modifying any code
that uses the shadow_proc method.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

3 files changed, 19 insertions, 82 deletions

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index a9806bc21ec3..c2b752341f89 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -374,9 +374,16 @@ static int proc_delete_dentry(struct dentry * dentry)
         return 1;
 }
 
+static int proc_revalidate_dentry(struct dentry *dentry, struct nameidata *nd)
+{
+        d_drop(dentry);
+        return 0;
+}
+
 static struct dentry_operations proc_dentry_operations =
 {
         .d_delete       = proc_delete_dentry,
+        .d_revalidate   = proc_revalidate_dentry,
 };
 
 /*
@@ -397,8 +404,11 @@ struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nam
                         if (de->namelen != dentry->d_name.len)
                                 continue;
                         if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
-                                unsigned int ino = de->low_ino;
+                                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);
                                 error = -EINVAL;
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 131f9c68be5f..0afe21ee0607 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -50,89 +50,14 @@ struct net *get_proc_net(const struct inode *inode)
 }
 EXPORT_SYMBOL_GPL(get_proc_net);
 
-static struct proc_dir_entry *proc_net_shadow;
+static struct proc_dir_entry *shadow_pde;
 
-static struct dentry *proc_net_shadow_dentry(struct dentry *parent,
+static struct proc_dir_entry *proc_net_shadow(struct task_struct *task,
                                                 struct proc_dir_entry *de)
 {
-        struct dentry *shadow = NULL;
-        struct inode *inode;
-        if (!de)
-                goto out;
-        de_get(de);
-        inode = proc_get_inode(parent->d_inode->i_sb, de->low_ino, de);
-        if (!inode)
-                goto out_de_put;
-        shadow = d_alloc_name(parent, de->name);
-        if (!shadow)
-                goto out_iput;
-        shadow->d_op = parent->d_op; /* proc_dentry_operations */
-        d_instantiate(shadow, inode);
-out:
-        return shadow;
-out_iput:
-        iput(inode);
-out_de_put:
-        de_put(de);
-        goto out;
-}
-
-static void *proc_net_follow_link(struct dentry *parent, struct nameidata *nd)
-{
-        struct net *net = current->nsproxy->net_ns;
-        struct dentry *shadow;
-        shadow = proc_net_shadow_dentry(parent, net->proc_net);
-        if (!shadow)
-                return ERR_PTR(-ENOENT);
-
-        dput(nd->dentry);
-        /* My dentry count is 1 and that should be enough as the
-         * shadow dentry is thrown away immediately.
-         */
-        nd->dentry = shadow;
-        return NULL;
+        return task->nsproxy->net_ns->proc_net;
 }
 
-static struct dentry *proc_net_lookup(struct inode *dir, struct dentry *dentry,
-                                      struct nameidata *nd)
-{
-        struct net *net = current->nsproxy->net_ns;
-        struct dentry *shadow;
-
-        shadow = proc_net_shadow_dentry(nd->dentry, net->proc_net);
-        if (!shadow)
-                return ERR_PTR(-ENOENT);
-
-        dput(nd->dentry);
-        nd->dentry = shadow;
-
-        return shadow->d_inode->i_op->lookup(shadow->d_inode, dentry, nd);
-}
-
-static int proc_net_setattr(struct dentry *dentry, struct iattr *iattr)
-{
-        struct net *net = current->nsproxy->net_ns;
-        struct dentry *shadow;
-        int ret;
-
-        shadow = proc_net_shadow_dentry(dentry->d_parent, net->proc_net);
-        if (!shadow)
-                return -ENOENT;
-        ret = shadow->d_inode->i_op->setattr(shadow, iattr);
-        dput(shadow);
-        return ret;
-}
-
-static const struct file_operations proc_net_dir_operations = {
-        .read                   = generic_read_dir,
-};
-
-static struct inode_operations proc_net_dir_inode_operations = {
-        .follow_link    = proc_net_follow_link,
-        .lookup         = proc_net_lookup,
-        .setattr        = proc_net_setattr,
-};
-
 static __net_init int proc_net_ns_init(struct net *net)
 {
         struct proc_dir_entry *root, *netd, *net_statd;
@@ -185,9 +110,8 @@ static struct pernet_operations __net_initdata proc_net_ns_ops = {
 
 int __init proc_net_init(void)
 {
-        proc_net_shadow = proc_mkdir("net", NULL);
-        proc_net_shadow->proc_iops = &proc_net_dir_inode_operations;
-        proc_net_shadow->proc_fops = &proc_net_dir_operations;
+        shadow_pde = proc_mkdir("net", NULL);
+        shadow_pde->shadow_proc = proc_net_shadow;
 
         return register_pernet_subsys(&proc_net_ns_ops);
 }
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 1273c6ec535c..523528d237b0 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -48,6 +48,8 @@ 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;
@@ -79,6 +81,7 @@ 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 {