From e5ff5ce6e20ee22511398bb31fb912466cf82a36 Mon Sep 17 00:00:00 2001 From: "Michael Kerrisk (man-pages)" Date: Wed, 25 Jan 2017 14:03:36 +1300 Subject: [PATCH 1/2] nsfs: Add an ioctl() to return the namespace type Linux 4.9 added two ioctl() operations that can be used to discover: * the parental relationships for hierarchical namespaces (user and PID) [NS_GET_PARENT] * the user namespaces that owns a specified non-user-namespace [NS_GET_USERNS] For no good reason that I can glean, NS_GET_USERNS was made synonymous with NS_GET_PARENT for user namespaces. It might have been better if NS_GET_USERNS had returned an error if the supplied file descriptor referred to a user namespace, since it suggests that the caller may be confused. More particularly, if it had generated an error, then I wouldn't need the new ioctl() operation proposed here. (On the other hand, what I propose here may be more generally useful.) I would like to write code that discovers namespace relationships for the purpose of understanding the namespace setup on a running system. In particular, given a file descriptor (or pathname) for a namespace, N, I'd like to obtain the corresponding user namespace. Namespace N might be a user namespace (in which case my code would just use N) or a non-user namespace (in which case my code will use NS_GET_USERNS to get the user namespace associated with N). The problem is that there is no way to tell the difference by looking at the file descriptor (and if I try to use NS_GET_USERNS on an N that is a user namespace, I get the parent user namespace of N, which is not what I want). This patch therefore adds a new ioctl(), NS_GET_NSTYPE, which, given a file descriptor that refers to a user namespace, returns the namespace type (one of the CLONE_NEW* constants). Signed-off-by: Michael Kerrisk Signed-off-by: Eric W. Biederman --- fs/nsfs.c | 2 ++ include/uapi/linux/nsfs.h | 3 +++ 2 files changed, 5 insertions(+) diff --git a/fs/nsfs.c b/fs/nsfs.c index 8c9fb29c6673..5d534763c662 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -172,6 +172,8 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl, if (!ns->ops->get_parent) return -EINVAL; return open_related_ns(ns, ns->ops->get_parent); + case NS_GET_NSTYPE: + return ns->ops->type; default: return -ENOTTY; } diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h index 3af617230d1b..2b48df11056a 100644 --- a/include/uapi/linux/nsfs.h +++ b/include/uapi/linux/nsfs.h @@ -9,5 +9,8 @@ #define NS_GET_USERNS _IO(NSIO, 0x1) /* Returns a file descriptor that refers to a parent namespace */ #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) #endif /* __LINUX_NSFS_H */ From d95fa3c76a66b6d76b1e109ea505c55e66360f3c Mon Sep 17 00:00:00 2001 From: "Michael Kerrisk (man-pages)" Date: Wed, 25 Jan 2017 14:04:15 +1300 Subject: [PATCH 2/2] nsfs: Add an ioctl() to return owner UID of a userns 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 a new NS_GET_CREATOR_UID ioctl() that fetches the UID (as seen in the user namespace of the caller) 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. If the owner UID does not have a mapping in the caller's user namespace return the overflow UID as that appears easier to deal with in practice in user-space applications. -- EWB Changed the handling of unmapped UIDs from -EOVERFLOW back to the overflow uid. Per conversation with Michael Kerrisk after examining his test code. Acked-by: Andrey Vagin Signed-off-by: Michael Kerrisk Signed-off-by: Eric W. Biederman --- 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 5d534763c662..1656843e87d2 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -7,6 +7,7 @@ #include #include #include +#include static struct vfsmount *nsfs_mnt; @@ -163,7 +164,10 @@ 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)); + uid_t __user *argp; + uid_t uid; 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 = (uid_t __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 2b48df11056a..1a3ca79f466b 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 (in the caller's user namespace) for a user namespace */ +#define NS_GET_OWNER_UID _IO(NSIO, 0x4) #endif /* __LINUX_NSFS_H */