[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>

1 files changed, 11 insertions, 1 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;