On Fri, Dec 23, 2016 at 10:54:53AM +0100, Michael Kerrisk (man-pages) wrote:
> I'd like to write code that discovers the user namespace hierarchy on
> a running system, and also shows who owns the various user namespaces.
> Currently, there is no way of getting the owner UID of a user
> namespace. Therefore, this patch adds an NS_GET_CREATOR_UID ioctl()
> that fetches the (munged) UID of the creator of the user namespace
> referred to by the specified file descriptor.
>
> If the supplied file descriptor does not refer to a user namespace,
> the operation fails with the error EINVAL.
>
Acked-by: Andrey Vagin <avagin@xxxxxxxxxx>
Here is one minor comment bellow
> Signed-off-by: Michael Kerrisk <mtk-manpages@xxxxxxxxx>
>
> ---
> V2 changes:
> * Renamed ioctl() from NS_CREATOR_UID to NS_OWNER_UID, at the
> suggestion of Eric Biederman.
> * Make ioctl() return UID via buffer pointed to by argp. (Returning
> the UID via the result value could lead to problems since a large
> unsigned int UID might be misinterpreted as an error.) Thanks to
> Andrei Vagin for pointing this out.
> ---
> fs/nsfs.c | 11 +++++++++++
> include/uapi/linux/nsfs.h | 8 +++++---
> 2 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nsfs.c b/fs/nsfs.c
> index 9f24b47..9c9277c 100644
> --- a/fs/nsfs.c
> +++ b/fs/nsfs.c
> @@ -7,6 +7,7 @@
> #include <linux/seq_file.h>
> #include <linux/user_namespace.h>
> #include <linux/nsfs.h>
> +#include <linux/uaccess.h>
>
> static struct vfsmount *nsfs_mnt;
>
> @@ -163,7 +164,10 @@ static int open_related_ns(struct ns_common *ns,
> static long ns_ioctl(struct file *filp, unsigned int ioctl,
> unsigned long arg)
> {
> + struct user_namespace *user_ns;
> struct ns_common *ns = get_proc_ns(file_inode(filp));
> + unsigned int __user *argp;
> + unsigned int uid;
I think it is better to use uid_t here
>
> switch (ioctl) {
> case NS_GET_USERNS:
> @@ -174,6 +178,13 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
> return open_related_ns(ns, ns->ops->get_parent);
> case NS_GET_NSTYPE:
> return ns->ops->type;
> + case NS_GET_OWNER_UID:
> + if (ns->ops->type != CLONE_NEWUSER)
> + return -EINVAL;
> + user_ns = container_of(ns, struct user_namespace, ns);
> + argp = (unsigned int __user *) arg;
> + uid = from_kuid_munged(current_user_ns(), user_ns->owner);
> + return put_user(uid, argp);
> default:
> return -ENOTTY;
> }
> diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
> index 2b48df1..c4a925e 100644
> --- a/include/uapi/linux/nsfs.h
> +++ b/include/uapi/linux/nsfs.h
> @@ -6,11 +6,13 @@
> #define NSIO 0xb7
>
> /* Returns a file descriptor that refers to an owning user namespace */
> -#define NS_GET_USERNS _IO(NSIO, 0x1)
> +#define NS_GET_USERNS _IO(NSIO, 0x1)
> /* Returns a file descriptor that refers to a parent namespace */
> -#define NS_GET_PARENT _IO(NSIO, 0x2)
> +#define NS_GET_PARENT _IO(NSIO, 0x2)
> /* Returns the type of namespace (CLONE_NEW* value) referred to by
> file descriptor */
> -#define NS_GET_NSTYPE _IO(NSIO, 0x3)
> +#define NS_GET_NSTYPE _IO(NSIO, 0x3)
> +/* Get owner UID for a user namespace */
> +#define NS_GET_OWNER_UID _IO(NSIO, 0x4)
>
> #endif /* __LINUX_NSFS_H */
> --
> 2.5.5
>
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