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

["Dmitry V. Levin" <ldv@strace.io>]

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