Re: [PATCH v2 00/12] make rpc_pipefs be mountable multiple time

Kirill A. Shutemov
2010-12-31T13:03:32Z

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On Thu, Dec 30, 2010 at 06:52:43AM -0600, Rob Landley wrote:
> On 12/30/2010 05:45 AM, Kirill A. Shutemov wrote:
> > Currently, there is no association between rpc_pipefs and mount namespace,
>
> There is in that the root context doesn't need to have this mounted, and
> new namespaces do. So there's an existing association between a LACK of
> a namespace and a different default behavior.
>
> My understanding (correct me if I'm wrong) is that the historical
> behavior is that there's only one, and it doesn't actually live anywhere
> in the filesystem tree. You're adding a special location. I'm
> wondering if there's any way for that location not to be special.

/var/lib/net/rpc_pipefs is default path where userspace part of NFS stack
(gssd, idmapd) want to see rpc_pipefs

> > so I don't see simple way to restrict number of rpc_pipefs per mount
> > namespace. Associating mount namespace with rpc_pipefs is not a good idea,
> > I think.
>
> I'm talking about associating a default rpc_pipefs instance with a
> namespace, which it seems to me you're already doing by emulating the
> legacy behavior. Before you CLONE_NEWNS you get a magic default mount
> that doesn't exist in the tree. After you CLONE_NEWNS you get something
> like -EINVAL unless you supply your own default.

Root namespace is special. In case of nfsroot you need rpc_pipefs before
root available.

> (I'm actually not sure
> why new namespaces don't fall back to the magic global one...)

It breaks isolation. Container should not use host's rpc_pipefs without
host's permission.

> I'm suggesting that if the user doesn't specify -o rpcmount then the
> default could be the first rpc_pipefs mount visible to the current
> process context, rather than a specific path. Logic to do that exists
> in the proc/self/mounts code (which I'm reading through now...).

static int check_rpc_pipefs(struct vfsmount *mnt, void *arg)
{
struct vfsmount **rpcmount = arg;
struct path path = {
.mnt = mnt,
.dentry = mnt->mnt_root,
};

if (!mnt->mnt_sb)
return 0;
if (mnt->mnt_sb->s_magic != RPCAUTH_GSSMAGIC)
return 0;

if (!path_is_under(&path, &current->fs->root))
return 0;

*rpcmount = mntget(mnt);
return 1;
}

struct vfsmount *get_rpc_pipefs(const char *p)
{
int error;
struct vfsmount *rpcmount = ERR_PTR(-EINVAL);
struct path path;

if (!p) {
iterate_mounts(check_rpc_pipefs, &rpcmount,
current->nsproxy->mnt_ns->root);

if (IS_ERR(rpcmount) && (current->nsproxy->mnt_ns ==
init_task.nsproxy->mnt_ns))
return mntget(init_rpc_pipefs);

return rpcmount;
}

error = kern_path(p, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
if (error)
return ERR_PTR(error);

check_rpc_pipefs(path.mnt, &rpcmount);
path_put(&path);

return rpcmount;
}
EXPORT_SYMBOL_GPL(get_rpc_pipefs);

Something like this? Patch to replace patch #10 attached.

--
Kirill A. Shutemov

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>From 36bdb502360461a8426821a37728aef3a3b8c738 Mon Sep 17 00:00:00 2001
From: Kirill A. Shutemov <kas@openvz.org>
Date: Mon, 20 Dec 2010 04:03:52 +0200
Subject: [PATCH] sunrpc: introduce get_rpc_pipefs()

Get rpc_pipefs mount point by path.

Signed-off-by: Kirill A. Shutemov <kas@openvz.org>
---
include/linux/sunrpc/rpc_pipe_fs.h | 2 +
net/sunrpc/rpc_pipe.c | 51 ++++++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+), 0 deletions(-)

diff --git a/include/linux/sunrpc/rpc_pipe_fs.h b/include/linux/sunrpc/rpc_pipe_fs.h
index b09bfa5..922057c 100644
--- a/include/linux/sunrpc/rpc_pipe_fs.h
+++ b/include/linux/sunrpc/rpc_pipe_fs.h
@@ -46,6 +46,8 @@ RPC_I(struct inode *inode)

extern struct vfsmount *init_rpc_pipefs;

+struct vfsmount *get_rpc_pipefs(const char *path);
+
extern int rpc_queue_upcall(struct inode *, struct rpc_pipe_msg *);

struct rpc_clnt;
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index b1e299b..4e09a90 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -16,6 +16,9 @@
#include <linux/namei.h>
#include <linux/fsnotify.h>
#include <linux/kernel.h>
+#include <linux/nsproxy.h>
+#include <linux/mnt_namespace.h>
+#include <linux/fs_struct.h>

#include <asm/ioctls.h>
#include <linux/fs.h>
@@ -931,6 +934,54 @@ static const struct super_operations s_ops = {

#define RPCAUTH_GSSMAGIC 0x67596969

+static int check_rpc_pipefs(struct vfsmount *mnt, void *arg)
+{
+ struct vfsmount **rpcmount = arg;
+ struct path path = {
+ .mnt = mnt,
+ .dentry = mnt->mnt_root,
+ };
+
+ if (!mnt->mnt_sb)
+ return 0;
+ if (mnt->mnt_sb->s_magic != RPCAUTH_GSSMAGIC)
+ return 0;
+
+ if (!path_is_under(&path, &current->fs->root))
+ return 0;
+
+ *rpcmount = mntget(mnt);
+ return 1;
+}
+
+struct vfsmount *get_rpc_pipefs(const char *p)
+{
+ int error;
+ struct vfsmount *rpcmount = ERR_PTR(-EINVAL);
+ struct path path;
+
+ if (!p) {
+ iterate_mounts(check_rpc_pipefs, &rpcmount,
+ current->nsproxy->mnt_ns->root);
+
+ if (IS_ERR(rpcmount) && (current->nsproxy->mnt_ns ==
+ init_task.nsproxy->mnt_ns))
+ return mntget(init_rpc_pipefs);
+
+ return rpcmount;
+ }
+
+ error = kern_path(p, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
+ if (error)
+ return ERR_PTR(error);
+
+ check_rpc_pipefs(path.mnt, &rpcmount);
+ path_put(&path);
+
+ return rpcmount;
+}
+EXPORT_SYMBOL_GPL(get_rpc_pipefs);
+
/*
* We have a single directory with 1 node in it.
*/
--
1.7.3.4