Re: [PATCH 7/8] fs: add an ioctl to get the mnt ns id from nsfs

Re: [PATCH 7/8] fs: add an ioctl to get the mnt ns id from nsfs

[Dmitry V. Levin]

Hi,

On Mon, Jun 24, 2024 at 11:49:50AM -0400, Josef Bacik wrote:
> In order to utilize the listmount() and statmount() extensions that
> allow us to call them on different namespaces we need a way to get the
> mnt namespace id from user space.  Add an ioctl to nsfs that will allow
> us to extract the mnt namespace id in order to make these new extensions
> usable.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/nsfs.c                 | 14 ++++++++++++++
>  include/uapi/linux/nsfs.h |  2 ++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/fs/nsfs.c b/fs/nsfs.c
> index 07e22a15ef02..af352dadffe1 100644
> --- a/fs/nsfs.c
> +++ b/fs/nsfs.c
> @@ -12,6 +12,7 @@
>  #include <linux/nsfs.h>
>  #include <linux/uaccess.h>
>  
> +#include "mount.h"
>  #include "internal.h"
>  
>  static struct vfsmount *nsfs_mnt;
> @@ -143,6 +144,19 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
>  		argp = (uid_t __user *) arg;
>  		uid = from_kuid_munged(current_user_ns(), user_ns->owner);
>  		return put_user(uid, argp);
> +	case NS_GET_MNTNS_ID: {
> +		struct mnt_namespace *mnt_ns;
> +		__u64 __user *idp;
> +		__u64 id;
> +
> +		if (ns->ops->type != CLONE_NEWNS)
> +			return -EINVAL;
> +
> +		mnt_ns = container_of(ns, struct mnt_namespace, ns);
> +		idp = (__u64 __user *)arg;
> +		id = mnt_ns->seq;
> +		return put_user(id, idp);
> +	}
>  	default:
>  		return -ENOTTY;
>  	}
> diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
> index a0c8552b64ee..56e8b1639b98 100644
> --- a/include/uapi/linux/nsfs.h
> +++ b/include/uapi/linux/nsfs.h
> @@ -15,5 +15,7 @@
>  #define NS_GET_NSTYPE		_IO(NSIO, 0x3)
>  /* Get owner UID (in the caller's user namespace) for a user namespace */
>  #define NS_GET_OWNER_UID	_IO(NSIO, 0x4)
> +/* Get the id for a mount namespace */
> +#define NS_GET_MNTNS_ID		_IO(NSIO, 0x5)

As the kernel is writing an object of type __u64,
this has to be defined to _IOR(NSIO, 0x5, __u64) instead,
see the corresponding comments in uapi/asm-generic/ioctl.h file.


-- 
ldv

Re: [PATCH 7/8] fs: add an ioctl to get the mnt ns id from nsfs

[Christian Brauner]

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On Tue, Jul 30, 2024 at 07:45:54PM GMT, Dmitry V. Levin wrote:
> Hi,
> 
> On Mon, Jun 24, 2024 at 11:49:50AM -0400, Josef Bacik wrote:
> > In order to utilize the listmount() and statmount() extensions that
> > allow us to call them on different namespaces we need a way to get the
> > mnt namespace id from user space.  Add an ioctl to nsfs that will allow
> > us to extract the mnt namespace id in order to make these new extensions
> > usable.
> > 
> > Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> > ---
> >  fs/nsfs.c                 | 14 ++++++++++++++
> >  include/uapi/linux/nsfs.h |  2 ++
> >  2 files changed, 16 insertions(+)
> > 
> > diff --git a/fs/nsfs.c b/fs/nsfs.c
> > index 07e22a15ef02..af352dadffe1 100644
> > --- a/fs/nsfs.c
> > +++ b/fs/nsfs.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/nsfs.h>
> >  #include <linux/uaccess.h>
> >  
> > +#include "mount.h"
> >  #include "internal.h"
> >  
> >  static struct vfsmount *nsfs_mnt;
> > @@ -143,6 +144,19 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
> >  		argp = (uid_t __user *) arg;
> >  		uid = from_kuid_munged(current_user_ns(), user_ns->owner);
> >  		return put_user(uid, argp);
> > +	case NS_GET_MNTNS_ID: {
> > +		struct mnt_namespace *mnt_ns;
> > +		__u64 __user *idp;
> > +		__u64 id;
> > +
> > +		if (ns->ops->type != CLONE_NEWNS)
> > +			return -EINVAL;
> > +
> > +		mnt_ns = container_of(ns, struct mnt_namespace, ns);
> > +		idp = (__u64 __user *)arg;
> > +		id = mnt_ns->seq;
> > +		return put_user(id, idp);
> > +	}
> >  	default:
> >  		return -ENOTTY;
> >  	}
> > diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
> > index a0c8552b64ee..56e8b1639b98 100644
> > --- a/include/uapi/linux/nsfs.h
> > +++ b/include/uapi/linux/nsfs.h
> > @@ -15,5 +15,7 @@
> >  #define NS_GET_NSTYPE		_IO(NSIO, 0x3)
> >  /* Get owner UID (in the caller's user namespace) for a user namespace */
> >  #define NS_GET_OWNER_UID	_IO(NSIO, 0x4)
> > +/* Get the id for a mount namespace */
> > +#define NS_GET_MNTNS_ID		_IO(NSIO, 0x5)
> 
> As the kernel is writing an object of type __u64,
> this has to be defined to _IOR(NSIO, 0x5, __u64) instead,
> see the corresponding comments in uapi/asm-generic/ioctl.h file.

Thanks for spotting that. I've pushed a fix to vfs.fixes. See the
appended patch.

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From c43a484ddff73f92739f0167c738eb6fd2df78b7 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Wed, 31 Jul 2024 07:47:27 +0200
Subject: [PATCH] nsfs: fix ioctl declaration

The kernel is writing an object of type __u64, so the ioctl has to be
defined to _IOR(NSIO, 0x5, __u64) instead of _IO(NSIO, 0x5).

Reported-by: Dmitry V. Levin <ldv@strace.io>
Link: https://lore.kernel.org/r/20240730164554.GA18486@altlinux.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 include/uapi/linux/nsfs.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
index b133211331f6..5fad3d0fcd70 100644
--- a/include/uapi/linux/nsfs.h
+++ b/include/uapi/linux/nsfs.h
@@ -3,6 +3,7 @@
 #define __LINUX_NSFS_H
 
 #include <linux/ioctl.h>
+#include <linux/types.h>
 
 #define NSIO	0xb7
 
@@ -16,7 +17,7 @@
 /* Get owner UID (in the caller's user namespace) for a user namespace */
 #define NS_GET_OWNER_UID	_IO(NSIO, 0x4)
 /* Get the id for a mount namespace */
-#define NS_GET_MNTNS_ID		_IO(NSIO, 0x5)
+#define NS_GET_MNTNS_ID		_IOR(NSIO, 0x5, __u64)
 /* Translate pid from target pid namespace into the caller's pid namespace. */
 #define NS_GET_PID_FROM_PIDNS	_IOR(NSIO, 0x6, int)
 /* Return thread-group leader id of pid in the callers pid namespace. */
-- 
2.43.0