Merge patch series "Support foreign mount namespace with statmount/listmount"

Josef Bacik <josef@toxicpanda.com> says:

Currently the only way to iterate over mount entries in mount namespaces that
aren't your own is to trawl through /proc in order to find /proc/$PID/mountinfo
for the mount namespace that you want.  This is hugely inefficient, so extend
both statmount() and listmount() to allow specifying a mount namespace id in
order to get to mounts in other mount namespaces.

There are a few components to this

1. Having a global index of the mount namespace based on the ->seq value in the
   mount namespace.  This gives us a unique identifier that isn't re-used.
2. Support looking up mount namespaces based on that unique identifier, and
   validating the user has permission to access the given mount namespace.
3. Provide a new ioctl() on nsfs in order to extract the unique identifier we
   can use for statmount() and listmount().

The code is relatively straightforward, and there is a selftest provided to
validate everything works properly.

This is based on vfs.all as of last week, so must be applied onto a tree that
has Christians error handling rework in this area.  If you wish you can pull the
tree directly here

https://github.com/josefbacik/linux/tree/listmount.combined

Christian and I collaborated on this series, which is why there's patches from
both of us in this series.

Christian Brauner (4):
  fs: relax permissions for listmount()
  fs: relax permissions for statmount()
  fs: Allow listmount() in foreign mount namespace
  fs: Allow statmount() in foreign mount namespace

Josef Bacik (4):
  fs: keep an index of current mount namespaces
  fs: export the mount ns id via statmount
  fs: add an ioctl to get the mnt ns id from nsfs
  selftests: add a test for the foreign mnt ns extensions

fs/mount.h                                    |   2 +
 fs/namespace.c                                | 240 ++++++++++--
 fs/nsfs.c                                     |  14 +
 include/uapi/linux/mount.h                    |   6 +-
 include/uapi/linux/nsfs.h                     |   2 +
 .../selftests/filesystems/statmount/Makefile  |   2 +-
 .../filesystems/statmount/statmount.h         |  46 +++
 .../filesystems/statmount/statmount_test.c    |  53 +--
 .../filesystems/statmount/statmount_test_ns.c | 360 ++++++++++++++++++
 9 files changed, 659 insertions(+), 66 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/statmount/statmount.h
 create mode 100644 tools/testing/selftests/filesystems/statmount/statmount_test_ns.c

Link: https://lore.kernel.org/r/cover.1719243756.git.josef@toxicpanda.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/mount.h

@@ -16,6 +16,8 @@ struct mnt_namespace {
 	u64 event;
 	unsigned int		nr_mounts; /* # of mounts in the namespace */
 	unsigned int		pending_mounts;
+	struct rb_node		mnt_ns_tree_node; /* node in the mnt_ns_tree */
+	refcount_t		passive; /* number references not pinning @mounts */
 } __randomize_layout;
 
 struct mnt_pcp {

fs/namespace.c

@@ -78,6 +78,8 @@ static struct kmem_cache *mnt_cache __ro_after_init;
 static DECLARE_RWSEM(namespace_sem);
 static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
+static DEFINE_RWLOCK(mnt_ns_tree_lock);
+static struct rb_root mnt_ns_tree = RB_ROOT; /* protected by mnt_ns_tree_lock */
 
 struct mount_kattr {
 	unsigned int attr_set;
@@ -103,6 +105,109 @@ EXPORT_SYMBOL_GPL(fs_kobj);
  */
 __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
 
+static int mnt_ns_cmp(u64 seq, const struct mnt_namespace *ns)
+{
+	u64 seq_b = ns->seq;
+
+	if (seq < seq_b)
+		return -1;
+	if (seq > seq_b)
+		return 1;
+	return 0;
+}
+
+static inline struct mnt_namespace *node_to_mnt_ns(const struct rb_node *node)
+{
+	if (!node)
+		return NULL;
+	return rb_entry(node, struct mnt_namespace, mnt_ns_tree_node);
+}
+
+static bool mnt_ns_less(struct rb_node *a, const struct rb_node *b)
+{
+	struct mnt_namespace *ns_a = node_to_mnt_ns(a);
+	struct mnt_namespace *ns_b = node_to_mnt_ns(b);
+	u64 seq_a = ns_a->seq;
+
+	return mnt_ns_cmp(seq_a, ns_b) < 0;
+}
+
+static void mnt_ns_tree_add(struct mnt_namespace *ns)
+{
+	guard(write_lock)(&mnt_ns_tree_lock);
+	rb_add(&ns->mnt_ns_tree_node, &mnt_ns_tree, mnt_ns_less);
+}
+
+static void mnt_ns_release(struct mnt_namespace *ns)
+{
+	lockdep_assert_not_held(&mnt_ns_tree_lock);
+
+	/* keep alive for {list,stat}mount() */
+	if (refcount_dec_and_test(&ns->passive)) {
+		put_user_ns(ns->user_ns);
+		kfree(ns);
+	}
+}
+DEFINE_FREE(mnt_ns_release, struct mnt_namespace *, if (_T) mnt_ns_release(_T))
+
+static void mnt_ns_tree_remove(struct mnt_namespace *ns)
+{
+	/* remove from global mount namespace list */
+	if (!is_anon_ns(ns)) {
+		guard(write_lock)(&mnt_ns_tree_lock);
+		rb_erase(&ns->mnt_ns_tree_node, &mnt_ns_tree);
+	}
+
+	mnt_ns_release(ns);
+}
+
+/*
+ * Returns the mount namespace which either has the specified id, or has the
+ * next smallest id afer the specified one.
+ */
+static struct mnt_namespace *mnt_ns_find_id_at(u64 mnt_ns_id)
+{
+	struct rb_node *node = mnt_ns_tree.rb_node;
+	struct mnt_namespace *ret = NULL;
+
+	lockdep_assert_held(&mnt_ns_tree_lock);
+
+	while (node) {
+		struct mnt_namespace *n = node_to_mnt_ns(node);
+
+		if (mnt_ns_id <= n->seq) {
+			ret = node_to_mnt_ns(node);
+			if (mnt_ns_id == n->seq)
+				break;
+			node = node->rb_left;
+		} else {
+			node = node->rb_right;
+		}
+	}
+	return ret;
+}
+
+/*
+ * Lookup a mount namespace by id and take a passive reference count. Taking a
+ * passive reference means the mount namespace can be emptied if e.g., the last
+ * task holding an active reference exits. To access the mounts of the
+ * namespace the @namespace_sem must first be acquired. If the namespace has
+ * already shut down before acquiring @namespace_sem, {list,stat}mount() will
+ * see that the mount rbtree of the namespace is empty.
+ */
+static struct mnt_namespace *lookup_mnt_ns(u64 mnt_ns_id)
+{
+       struct mnt_namespace *ns;
+
+       guard(read_lock)(&mnt_ns_tree_lock);
+       ns = mnt_ns_find_id_at(mnt_ns_id);
+       if (!ns || ns->seq != mnt_ns_id)
+               return NULL;
+
+       refcount_inc(&ns->passive);
+       return ns;
+}
+
 static inline void lock_mount_hash(void)
 {
 	write_seqlock(&mount_lock);
@@ -3733,8 +3838,7 @@ static void free_mnt_ns(struct mnt_namespace *ns)
 	if (!is_anon_ns(ns))
 		ns_free_inum(&ns->ns);
 	dec_mnt_namespaces(ns->ucounts);
-	put_user_ns(ns->user_ns);
-	kfree(ns);
+	mnt_ns_tree_remove(ns);
 }
 
 /*
@@ -3773,7 +3877,9 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool a
 	if (!anon)
 		new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
 	refcount_set(&new_ns->ns.count, 1);
+	refcount_set(&new_ns->passive, 1);
 	new_ns->mounts = RB_ROOT;
+	RB_CLEAR_NODE(&new_ns->mnt_ns_tree_node);
 	init_waitqueue_head(&new_ns->poll);
 	new_ns->user_ns = get_user_ns(user_ns);
 	new_ns->ucounts = ucounts;
@@ -3850,6 +3956,7 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 		while (p->mnt.mnt_root != q->mnt.mnt_root)
 			p = next_mnt(skip_mnt_tree(p), old);
 	}
+	mnt_ns_tree_add(new_ns);
 	namespace_unlock();
 
 	if (rootmnt)
@@ -4867,6 +4974,12 @@ static int statmount_fs_type(struct kstatmount *s, struct seq_file *seq)
 	return 0;
 }
 
+static void statmount_mnt_ns_id(struct kstatmount *s, struct mnt_namespace *ns)
+{
+	s->sm.mask |= STATMOUNT_MNT_NS_ID;
+	s->sm.mnt_ns_id = ns->seq;
+}
+
 static int statmount_string(struct kstatmount *s, u64 flag)
 {
 	int ret;
@@ -4930,6 +5043,7 @@ static int copy_statmount_to_user(struct kstatmount *s)
 static int do_statmount(struct kstatmount *s)
 {
 	struct mount *m = real_mount(s->mnt);
+	struct mnt_namespace *ns = m->mnt_ns;
 	int err;
 
 	/*
@@ -4937,7 +5051,7 @@ static int do_statmount(struct kstatmount *s)
 	 * mounts to show users.
 	 */
 	if (!is_path_reachable(m, m->mnt.mnt_root, &s->root) &&
-	    !ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN))
+	    !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 
 	err = security_sb_statfs(s->mnt->mnt_root);
@@ -4962,6 +5076,9 @@ static int do_statmount(struct kstatmount *s)
 	if (!err && s->mask & STATMOUNT_MNT_POINT)
 		err = statmount_string(s, STATMOUNT_MNT_POINT);
 
+	if (!err && s->mask & STATMOUNT_MNT_NS_ID)
+		statmount_mnt_ns_id(s, ns);
+
 	if (err)
 		return err;
 
@@ -5003,7 +5120,7 @@ static int copy_mnt_id_req(const struct mnt_id_req __user *req,
 	int ret;
 	size_t usize;
 
-	BUILD_BUG_ON(sizeof(struct mnt_id_req) != MNT_ID_REQ_SIZE_VER0);
+	BUILD_BUG_ON(sizeof(struct mnt_id_req) != MNT_ID_REQ_SIZE_VER1);
 
 	ret = get_user(usize, &req->size);
 	if (ret)
@@ -5021,10 +5138,63 @@ static int copy_mnt_id_req(const struct mnt_id_req __user *req,
 	return 0;
 }
 
+static struct mount *listmnt_next(struct mount *curr, bool reverse)
+{
+	struct rb_node *node;
+
+	if (reverse)
+		node = rb_prev(&curr->mnt_node);
+	else
+		node = rb_next(&curr->mnt_node);
+
+	return node_to_mount(node);
+}
+
+static int grab_requested_root(struct mnt_namespace *ns, struct path *root)
+{
+	struct mount *first;
+
+	rwsem_assert_held(&namespace_sem);
+
+	/* We're looking at our own ns, just use get_fs_root. */
+	if (ns == current->nsproxy->mnt_ns) {
+		get_fs_root(current->fs, root);
+		return 0;
+	}
+
+	/*
+	 * We have to find the first mount in our ns and use that, however it
+	 * may not exist, so handle that properly.
+	 */
+	if (RB_EMPTY_ROOT(&ns->mounts))
+		return -ENOENT;
+
+	first = listmnt_next(ns->root, false);
+	if (!first)
+		return -ENOENT;
+	root->mnt = mntget(&first->mnt);
+	root->dentry = dget(root->mnt->mnt_root);
+	return 0;
+}
+
+/*
+ * If the user requested a specific mount namespace id, look that up and return
+ * that, or if not simply grab a passive reference on our mount namespace and
+ * return that.
+ */
+static struct mnt_namespace *grab_requested_mnt_ns(u64 mnt_ns_id)
+{
+	if (mnt_ns_id)
+		return lookup_mnt_ns(mnt_ns_id);
+	refcount_inc(&current->nsproxy->mnt_ns->passive);
+	return current->nsproxy->mnt_ns;
+}
+
 SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
 		struct statmount __user *, buf, size_t, bufsize,
 		unsigned int, flags)
 {
+	struct mnt_namespace *ns __free(mnt_ns_release) = NULL;
 	struct vfsmount *mnt;
 	struct mnt_id_req kreq;
 	struct kstatmount ks;
@@ -5039,13 +5209,28 @@ SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
 	if (ret)
 		return ret;
 
+	ns = grab_requested_mnt_ns(kreq.mnt_ns_id);
+	if (!ns)
+		return -ENOENT;
+
+	if (kreq.mnt_ns_id && (ns != current->nsproxy->mnt_ns) &&
+	    !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
+		return -ENOENT;
+
 retry:
 	ret = prepare_kstatmount(&ks, &kreq, buf, bufsize, seq_size);
 	if (ret)
 		return ret;
 
 	down_read(&namespace_sem);
-	mnt = lookup_mnt_in_ns(kreq.mnt_id, current->nsproxy->mnt_ns);
+	/* Has the namespace already been emptied? */
+	if (kreq.mnt_ns_id && RB_EMPTY_ROOT(&ns->mounts)) {
+		up_read(&namespace_sem);
+		kvfree(ks.seq.buf);
+		return -ENOENT;
+	}
+
+	mnt = lookup_mnt_in_ns(kreq.mnt_id, ns);
 	if (!mnt) {
 		up_read(&namespace_sem);
 		kvfree(ks.seq.buf);
@@ -5053,7 +5238,12 @@ SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
 	}
 
 	ks.mnt = mnt;
-	get_fs_root(current->fs, &ks.root);
+	ret = grab_requested_root(ns, &ks.root);
+	if (ret) {
+		up_read(&namespace_sem);
+		kvfree(ks.seq.buf);
+		return ret;
+	}
 	ret = do_statmount(&ks);
 	path_put(&ks.root);
 	up_read(&namespace_sem);
@@ -5066,30 +5256,21 @@ SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
 	return ret;
 }
 
-static struct mount *listmnt_next(struct mount *curr, bool reverse)
-{
-	struct rb_node *node;
-
-	if (reverse)
-		node = rb_prev(&curr->mnt_node);
-	else
-		node = rb_next(&curr->mnt_node);
-
-	return node_to_mount(node);
-}
-
-static ssize_t do_listmount(u64 mnt_parent_id, u64 last_mnt_id, u64 *mnt_ids,
-			    size_t nr_mnt_ids, bool reverse)
+static ssize_t do_listmount(struct mnt_namespace *ns, u64 mnt_parent_id,
+			    u64 last_mnt_id, u64 *mnt_ids, size_t nr_mnt_ids,
+			    bool reverse)
 {
 	struct path root __free(path_put) = {};
-	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
 	struct path orig;
 	struct mount *r, *first;
 	ssize_t ret;
 
 	rwsem_assert_held(&namespace_sem);
 
-	get_fs_root(current->fs, &root);
+	ret = grab_requested_root(ns, &root);
+	if (ret)
+		return ret;
+
 	if (mnt_parent_id == LSMT_ROOT) {
 		orig = root;
 	} else {
@@ -5104,7 +5285,7 @@ static ssize_t do_listmount(u64 mnt_parent_id, u64 last_mnt_id, u64 *mnt_ids,
 	 * mounts to show users.
 	 */
 	if (!is_path_reachable(real_mount(orig.mnt), orig.dentry, &root) &&
-	    !ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN))
+	    !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 
 	ret = security_sb_statfs(orig.dentry);
@@ -5141,6 +5322,7 @@ SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
 {
 	u64 *kmnt_ids __free(kvfree) = NULL;
 	const size_t maxcount = 1000000;
+	struct mnt_namespace *ns __free(mnt_ns_release) = NULL;
 	struct mnt_id_req kreq;
 	ssize_t ret;
 
@@ -5167,8 +5349,16 @@ SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
 	if (!kmnt_ids)
 		return -ENOMEM;
 
+	ns = grab_requested_mnt_ns(kreq.mnt_ns_id);
+	if (!ns)
+		return -ENOENT;
+
+	if (kreq.mnt_ns_id && (ns != current->nsproxy->mnt_ns) &&
+	    !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
+		return -ENOENT;
+
 	scoped_guard(rwsem_read, &namespace_sem)
-		ret = do_listmount(kreq.mnt_id, kreq.param, kmnt_ids,
+		ret = do_listmount(ns, kreq.mnt_id, kreq.param, kmnt_ids,
 				   nr_mnt_ids, (flags & LISTMOUNT_REVERSE));
 
 	if (copy_to_user(mnt_ids, kmnt_ids, ret * sizeof(*mnt_ids)))
@@ -5204,6 +5394,8 @@ static void __init init_mount_tree(void)
 
 	set_fs_pwd(current->fs, &root);
 	set_fs_root(current->fs, &root);
+
+	mnt_ns_tree_add(ns);
 }
 
 void __init mnt_init(void)

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;
 	}

include/uapi/linux/mount.h

@@ -172,7 +172,8 @@ struct statmount {
 	__u64 propagate_from;	/* Propagation from in current namespace */
 	__u32 mnt_root;		/* [str] Root of mount relative to root of fs */
 	__u32 mnt_point;	/* [str] Mountpoint relative to current root */
-	__u64 __spare2[50];
+	__u64 mnt_ns_id;	/* ID of the mount namespace */
+	__u64 __spare2[49];
 	char str[];		/* Variable size part containing strings */
 };
 
@@ -188,10 +189,12 @@ struct mnt_id_req {
 	__u32 spare;
 	__u64 mnt_id;
 	__u64 param;
+	__u64 mnt_ns_id;
 };
 
 /* List of all mnt_id_req versions. */
 #define MNT_ID_REQ_SIZE_VER0	24 /* sizeof first published struct */
+#define MNT_ID_REQ_SIZE_VER1	32 /* sizeof second published struct */
 
 /*
  * @mask bits for statmount(2)
@@ -202,6 +205,7 @@ struct mnt_id_req {
 #define STATMOUNT_MNT_ROOT		0x00000008U	/* Want/got mnt_root  */
 #define STATMOUNT_MNT_POINT		0x00000010U	/* Want/got mnt_point */
 #define STATMOUNT_FS_TYPE		0x00000020U	/* Want/got fs_type */
+#define STATMOUNT_MNT_NS_ID		0x00000040U	/* Want/got mnt_ns_id */
 
 /*
  * Special @mnt_id values that can be passed to listmount

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)
 
 #endif /* __LINUX_NSFS_H */

tools/testing/selftests/filesystems/statmount/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
 CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
-TEST_GEN_PROGS := statmount_test
+TEST_GEN_PROGS := statmount_test statmount_test_ns
 
 include ../../lib.mk

tools/testing/selftests/filesystems/statmount/statmount.h

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __STATMOUNT_H
+#define __STATMOUNT_H
+
+#include <stdint.h>
+#include <linux/mount.h>
+#include <asm/unistd.h>
+
+static inline int statmount(uint64_t mnt_id, uint64_t mnt_ns_id, uint64_t mask,
+			    struct statmount *buf, size_t bufsize,
+			    unsigned int flags)
+{
+	struct mnt_id_req req = {
+		.size = MNT_ID_REQ_SIZE_VER0,
+		.mnt_id = mnt_id,
+		.param = mask,
+	};
+
+	if (mnt_ns_id) {
+		req.size = MNT_ID_REQ_SIZE_VER1;
+		req.mnt_ns_id = mnt_ns_id;
+	}
+
+	return syscall(__NR_statmount, &req, buf, bufsize, flags);
+}
+
+static ssize_t listmount(uint64_t mnt_id, uint64_t mnt_ns_id,
+			 uint64_t last_mnt_id, uint64_t list[], size_t num,
+			 unsigned int flags)
+{
+	struct mnt_id_req req = {
+		.size = MNT_ID_REQ_SIZE_VER0,
+		.mnt_id = mnt_id,
+		.param = last_mnt_id,
+	};
+
+	if (mnt_ns_id) {
+		req.size = MNT_ID_REQ_SIZE_VER1;
+		req.mnt_ns_id = mnt_ns_id;
+	}
+
+	return syscall(__NR_listmount, &req, list, num, flags);
+}
+
+#endif /* __STATMOUNT_H */

tools/testing/selftests/filesystems/statmount/statmount_test.c

@@ -4,17 +4,15 @@
 
 #include <assert.h>
 #include <stddef.h>
-#include <stdint.h>
 #include <sched.h>
 #include <fcntl.h>
 #include <sys/param.h>
 #include <sys/mount.h>
 #include <sys/stat.h>
 #include <sys/statfs.h>
-#include <linux/mount.h>
 #include <linux/stat.h>
-#include <asm/unistd.h>
 
+#include "statmount.h"
 #include "../../kselftest.h"
 
 static const char *const known_fs[] = {
@@ -36,18 +34,6 @@ static const char *const known_fs[] = {
 	"ufs", "v7", "vboxsf", "vfat", "virtiofs", "vxfs", "xenfs", "xfs",
 	"zonefs", NULL };
 
-static int statmount(uint64_t mnt_id, uint64_t mask, struct statmount *buf,
-		     size_t bufsize, unsigned int flags)
-{
-	struct mnt_id_req req = {
-		.size = MNT_ID_REQ_SIZE_VER0,
-		.mnt_id = mnt_id,
-		.param = mask,
-	};
-
-	return syscall(__NR_statmount, &req, buf, bufsize, flags);
-}
-
 static struct statmount *statmount_alloc(uint64_t mnt_id, uint64_t mask, unsigned int flags)
 {
 	size_t bufsize = 1 << 15;
@@ -56,7 +42,7 @@ static struct statmount *statmount_alloc(uint64_t mnt_id, uint64_t mask, unsigne
 	int ret;
 
 	for (;;) {
-		ret = statmount(mnt_id, mask, tmp, bufsize, flags);
+		ret = statmount(mnt_id, 0, mask, tmp, bufsize, flags);
 		if (ret != -1)
 			break;
 		if (tofree)
@@ -122,7 +108,6 @@ static int orig_root;
 static uint64_t root_id, parent_id;
 static uint32_t old_root_id, old_parent_id;
 
-
 static void cleanup_namespace(void)
 {
 	fchdir(orig_root);
@@ -138,7 +123,7 @@ static void setup_namespace(void)
 	uid_t uid = getuid();
 	gid_t gid = getgid();
 
-	ret = unshare(CLONE_NEWNS|CLONE_NEWUSER);
+	ret = unshare(CLONE_NEWNS|CLONE_NEWUSER|CLONE_NEWPID);
 	if (ret == -1)
 		ksft_exit_fail_msg("unsharing mountns and userns: %s\n",
 				   strerror(errno));
@@ -208,25 +193,13 @@ static int setup_mount_tree(int log2_num)
 	return 0;
 }
 
-static ssize_t listmount(uint64_t mnt_id, uint64_t last_mnt_id,
-			 uint64_t list[], size_t num, unsigned int flags)
-{
-	struct mnt_id_req req = {
-		.size = MNT_ID_REQ_SIZE_VER0,
-		.mnt_id = mnt_id,
-		.param = last_mnt_id,
-	};
-
-	return syscall(__NR_listmount, &req, list, num, flags);
-}
-
 static void test_listmount_empty_root(void)
 {
 	ssize_t res;
 	const unsigned int size = 32;
 	uint64_t list[size];
 
-	res = listmount(LSMT_ROOT, 0, list, size, 0);
+	res = listmount(LSMT_ROOT, 0, 0, list, size, 0);
 	if (res == -1) {
 		ksft_test_result_fail("listmount: %s\n", strerror(errno));
 		return;
@@ -251,7 +224,7 @@ static void test_statmount_zero_mask(void)
 	struct statmount sm;
 	int ret;
 
-	ret = statmount(root_id, 0, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, 0, &sm, sizeof(sm), 0);
 	if (ret == -1) {
 		ksft_test_result_fail("statmount zero mask: %s\n",
 				      strerror(errno));
@@ -277,7 +250,7 @@ static void test_statmount_mnt_basic(void)
 	int ret;
 	uint64_t mask = STATMOUNT_MNT_BASIC;
 
-	ret = statmount(root_id, mask, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, mask, &sm, sizeof(sm), 0);
 	if (ret == -1) {
 		ksft_test_result_fail("statmount mnt basic: %s\n",
 				      strerror(errno));
@@ -337,7 +310,7 @@ static void test_statmount_sb_basic(void)
 	struct statx sx;
 	struct statfs sf;
 
-	ret = statmount(root_id, mask, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, mask, &sm, sizeof(sm), 0);
 	if (ret == -1) {
 		ksft_test_result_fail("statmount sb basic: %s\n",
 				      strerror(errno));
@@ -498,14 +471,14 @@ static void test_statmount_string(uint64_t mask, size_t off, const char *name)
 	exactsize = sm->size;
 	shortsize = sizeof(*sm) + i;
 
-	ret = statmount(root_id, mask, sm, exactsize, 0);
+	ret = statmount(root_id, 0, mask, sm, exactsize, 0);
 	if (ret == -1) {
 		ksft_test_result_fail("statmount exact size: %s\n",
 				      strerror(errno));
 		goto out;
 	}
 	errno = 0;
-	ret = statmount(root_id, mask, sm, shortsize, 0);
+	ret = statmount(root_id, 0, mask, sm, shortsize, 0);
 	if (ret != -1 || errno != EOVERFLOW) {
 		ksft_test_result_fail("should have failed with EOVERFLOW: %s\n",
 				      strerror(errno));
@@ -533,7 +506,7 @@ static void test_listmount_tree(void)
 	if (res == -1)
 		return;
 
-	num = res = listmount(LSMT_ROOT, 0, list, size, 0);
+	num = res = listmount(LSMT_ROOT, 0, 0, list, size, 0);
 	if (res == -1) {
 		ksft_test_result_fail("listmount: %s\n", strerror(errno));
 		return;
@@ -545,7 +518,7 @@ static void test_listmount_tree(void)
 	}
 
 	for (i = 0; i < size - step;) {
-		res = listmount(LSMT_ROOT, i ? list2[i - 1] : 0, list2 + i, step, 0);
+		res = listmount(LSMT_ROOT, 0, i ? list2[i - 1] : 0, list2 + i, step, 0);
 		if (res == -1)
 			ksft_test_result_fail("short listmount: %s\n",
 					      strerror(errno));
@@ -577,11 +550,11 @@ int main(void)
 	int ret;
 	uint64_t all_mask = STATMOUNT_SB_BASIC | STATMOUNT_MNT_BASIC |
 		STATMOUNT_PROPAGATE_FROM | STATMOUNT_MNT_ROOT |
-		STATMOUNT_MNT_POINT | STATMOUNT_FS_TYPE;
+		STATMOUNT_MNT_POINT | STATMOUNT_FS_TYPE | STATMOUNT_MNT_NS_ID;
 
 	ksft_print_header();
 
-	ret = statmount(0, 0, NULL, 0, 0);
+	ret = statmount(0, 0, 0, NULL, 0, 0);
 	assert(ret == -1);
 	if (errno == ENOSYS)
 		ksft_exit_skip("statmount() syscall not supported\n");

tools/testing/selftests/filesystems/statmount/statmount_test_ns.c

@@ -0,0 +1,364 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define _GNU_SOURCE
+
+#include <assert.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdlib.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <linux/nsfs.h>
+#include <linux/stat.h>
+
+#include "statmount.h"
+#include "../../kselftest.h"
+
+#define NSID_PASS 0
+#define NSID_FAIL 1
+#define NSID_SKIP 2
+#define NSID_ERROR 3
+
+static void handle_result(int ret, const char *testname)
+{
+	if (ret == NSID_PASS)
+		ksft_test_result_pass("%s\n", testname);
+	else if (ret == NSID_FAIL)
+		ksft_test_result_fail("%s\n", testname);
+	else if (ret == NSID_ERROR)
+		ksft_exit_fail_msg("%s\n", testname);
+	else
+		ksft_test_result_skip("%s\n", testname);
+}
+
+static inline int wait_for_pid(pid_t pid)
+{
+	int status, ret;
+
+again:
+	ret = waitpid(pid, &status, 0);
+	if (ret == -1) {
+		if (errno == EINTR)
+			goto again;
+
+		ksft_print_msg("waitpid returned -1, errno=%d\n", errno);
+		return -1;
+	}
+
+	if (!WIFEXITED(status)) {
+		ksft_print_msg(
+		       "waitpid !WIFEXITED, WIFSIGNALED=%d, WTERMSIG=%d\n",
+		       WIFSIGNALED(status), WTERMSIG(status));
+		return -1;
+	}
+
+	ret = WEXITSTATUS(status);
+	return ret;
+}
+
+static int get_mnt_ns_id(const char *mnt_ns, uint64_t *mnt_ns_id)
+{
+	int fd = open(mnt_ns, O_RDONLY);
+
+	if (fd < 0) {
+		ksft_print_msg("failed to open for ns %s: %s\n",
+			       mnt_ns, strerror(errno));
+		sleep(60);
+		return NSID_ERROR;
+	}
+
+	if (ioctl(fd, NS_GET_MNTNS_ID, mnt_ns_id) < 0) {
+		ksft_print_msg("failed to get the nsid for ns %s: %s\n",
+			       mnt_ns, strerror(errno));
+		return NSID_ERROR;
+	}
+	close(fd);
+	return NSID_PASS;
+}
+
+static int get_mnt_id(const char *path, uint64_t *mnt_id)
+{
+	struct statx sx;
+	int ret;
+
+	ret = statx(AT_FDCWD, path, 0, STATX_MNT_ID_UNIQUE, &sx);
+	if (ret == -1) {
+		ksft_print_msg("retrieving unique mount ID for %s: %s\n", path,
+			       strerror(errno));
+		return NSID_ERROR;
+	}
+
+	if (!(sx.stx_mask & STATX_MNT_ID_UNIQUE)) {
+		ksft_print_msg("no unique mount ID available for %s\n", path);
+		return NSID_ERROR;
+	}
+
+	*mnt_id = sx.stx_mnt_id;
+	return NSID_PASS;
+}
+
+static int write_file(const char *path, const char *val)
+{
+	int fd = open(path, O_WRONLY);
+	size_t len = strlen(val);
+	int ret;
+
+	if (fd == -1) {
+		ksft_print_msg("opening %s for write: %s\n", path, strerror(errno));
+		return NSID_ERROR;
+	}
+
+	ret = write(fd, val, len);
+	if (ret == -1) {
+		ksft_print_msg("writing to %s: %s\n", path, strerror(errno));
+		return NSID_ERROR;
+	}
+	if (ret != len) {
+		ksft_print_msg("short write to %s\n", path);
+		return NSID_ERROR;
+	}
+
+	ret = close(fd);
+	if (ret == -1) {
+		ksft_print_msg("closing %s\n", path);
+		return NSID_ERROR;
+	}
+
+	return NSID_PASS;
+}
+
+static int setup_namespace(void)
+{
+	int ret;
+	char buf[32];
+	uid_t uid = getuid();
+	gid_t gid = getgid();
+
+	ret = unshare(CLONE_NEWNS|CLONE_NEWUSER|CLONE_NEWPID);
+	if (ret == -1)
+		ksft_exit_fail_msg("unsharing mountns and userns: %s\n",
+				   strerror(errno));
+
+	sprintf(buf, "0 %d 1", uid);
+	ret = write_file("/proc/self/uid_map", buf);
+	if (ret != NSID_PASS)
+		return ret;
+	ret = write_file("/proc/self/setgroups", "deny");
+	if (ret != NSID_PASS)
+		return ret;
+	sprintf(buf, "0 %d 1", gid);
+	ret = write_file("/proc/self/gid_map", buf);
+	if (ret != NSID_PASS)
+		return ret;
+
+	ret = mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL);
+	if (ret == -1) {
+		ksft_print_msg("making mount tree private: %s\n",
+			       strerror(errno));
+		return NSID_ERROR;
+	}
+
+	return NSID_PASS;
+}
+
+static int _test_statmount_mnt_ns_id(void)
+{
+	struct statmount sm;
+	uint64_t mnt_ns_id;
+	uint64_t root_id;
+	int ret;
+
+	ret = get_mnt_ns_id("/proc/self/ns/mnt", &mnt_ns_id);
+	if (ret != NSID_PASS)
+		return ret;
+
+	ret = get_mnt_id("/", &root_id);
+	if (ret != NSID_PASS)
+		return ret;
+
+	ret = statmount(root_id, 0, STATMOUNT_MNT_NS_ID, &sm, sizeof(sm), 0);
+	if (ret == -1) {
+		ksft_print_msg("statmount mnt ns id: %s\n", strerror(errno));
+		return NSID_ERROR;
+	}
+
+	if (sm.size != sizeof(sm)) {
+		ksft_print_msg("unexpected size: %u != %u\n", sm.size,
+			       (uint32_t)sizeof(sm));
+		return NSID_FAIL;
+	}
+	if (sm.mask != STATMOUNT_MNT_NS_ID) {
+		ksft_print_msg("statmount mnt ns id unavailable\n");
+		return NSID_SKIP;
+	}
+
+	if (sm.mnt_ns_id != mnt_ns_id) {
+		ksft_print_msg("unexpected mnt ns ID: 0x%llx != 0x%llx\n",
+			       (unsigned long long)sm.mnt_ns_id,
+			       (unsigned long long)mnt_ns_id);
+		return NSID_FAIL;
+	}
+
+	return NSID_PASS;
+}
+
+static void test_statmount_mnt_ns_id(void)
+{
+	pid_t pid;
+	int ret;
+
+	pid = fork();
+	if (pid < 0)
+		ksft_exit_fail_msg("failed to fork: %s\n", strerror(errno));
+
+	/* We're the original pid, wait for the result. */
+	if (pid != 0) {
+		ret = wait_for_pid(pid);
+		handle_result(ret, "test statmount ns id");
+		return;
+	}
+
+	ret = setup_namespace();
+	if (ret != NSID_PASS)
+		exit(ret);
+	ret = _test_statmount_mnt_ns_id();
+	exit(ret);
+}
+
+static int validate_external_listmount(pid_t pid, uint64_t child_nr_mounts)
+{
+	uint64_t list[256];
+	uint64_t mnt_ns_id;
+	uint64_t nr_mounts;
+	char buf[256];
+	int ret;
+
+	/* Get the mount ns id for our child. */
+	snprintf(buf, sizeof(buf), "/proc/%lu/ns/mnt", (unsigned long)pid);
+	ret = get_mnt_ns_id(buf, &mnt_ns_id);
+
+	nr_mounts = listmount(LSMT_ROOT, mnt_ns_id, 0, list, 256, 0);
+	if (nr_mounts == (uint64_t)-1) {
+		ksft_print_msg("listmount: %s\n", strerror(errno));
+		return NSID_ERROR;
+	}
+
+	if (nr_mounts != child_nr_mounts) {
+		ksft_print_msg("listmount results is %zi != %zi\n", nr_mounts,
+			       child_nr_mounts);
+		return NSID_FAIL;
+	}
+
+	/* Validate that all of our entries match our mnt_ns_id. */
+	for (int i = 0; i < nr_mounts; i++) {
+		struct statmount sm;
+
+		ret = statmount(list[i], mnt_ns_id, STATMOUNT_MNT_NS_ID, &sm,
+				sizeof(sm), 0);
+		if (ret < 0) {
+			ksft_print_msg("statmount mnt ns id: %s\n", strerror(errno));
+			return NSID_ERROR;
+		}
+
+		if (sm.mask != STATMOUNT_MNT_NS_ID) {
+			ksft_print_msg("statmount mnt ns id unavailable\n");
+			return NSID_SKIP;
+		}
+
+		if (sm.mnt_ns_id != mnt_ns_id) {
+			ksft_print_msg("listmount gave us the wrong ns id: 0x%llx != 0x%llx\n",
+				       (unsigned long long)sm.mnt_ns_id,
+				       (unsigned long long)mnt_ns_id);
+			return NSID_FAIL;
+		}
+	}
+
+	return NSID_PASS;
+}
+
+static void test_listmount_ns(void)
+{
+	uint64_t nr_mounts;
+	char pval;
+	int child_ready_pipe[2];
+	int parent_ready_pipe[2];
+	pid_t pid;
+	int ret, child_ret;
+
+	if (pipe(child_ready_pipe) < 0)
+		ksft_exit_fail_msg("failed to create the child pipe: %s\n",
+				   strerror(errno));
+	if (pipe(parent_ready_pipe) < 0)
+		ksft_exit_fail_msg("failed to create the parent pipe: %s\n",
+				   strerror(errno));
+
+	pid = fork();
+	if (pid < 0)
+		ksft_exit_fail_msg("failed to fork: %s\n", strerror(errno));
+
+	if (pid == 0) {
+		char cval;
+		uint64_t list[256];
+
+		close(child_ready_pipe[0]);
+		close(parent_ready_pipe[1]);
+
+		ret = setup_namespace();
+		if (ret != NSID_PASS)
+			exit(ret);
+
+		nr_mounts = listmount(LSMT_ROOT, 0, 0, list, 256, 0);
+		if (nr_mounts == (uint64_t)-1) {
+			ksft_print_msg("listmount: %s\n", strerror(errno));
+			exit(NSID_FAIL);
+		}
+
+		/*
+		 * Tell our parent how many mounts we have, and then wait for it
+		 * to tell us we're done.
+		 */
+		write(child_ready_pipe[1], &nr_mounts, sizeof(nr_mounts));
+		read(parent_ready_pipe[0], &cval, sizeof(cval));
+		exit(NSID_PASS);
+	}
+
+	close(child_ready_pipe[1]);
+	close(parent_ready_pipe[0]);
+
+	/* Wait until the child has created everything. */
+	if (read(child_ready_pipe[0], &nr_mounts, sizeof(nr_mounts)) !=
+	    sizeof(nr_mounts))
+		ret = NSID_ERROR;
+
+	ret = validate_external_listmount(pid, nr_mounts);
+
+	if (write(parent_ready_pipe[1], &pval, sizeof(pval)) != sizeof(pval))
+		ret = NSID_ERROR;
+
+	child_ret = wait_for_pid(pid);
+	if (child_ret != NSID_PASS)
+		ret = child_ret;
+	handle_result(ret, "test listmount ns id");
+}
+
+int main(void)
+{
+	int ret;
+
+	ksft_print_header();
+	ret = statmount(0, 0, 0, NULL, 0, 0);
+	assert(ret == -1);
+	if (errno == ENOSYS)
+		ksft_exit_skip("statmount() syscall not supported\n");
+
+	ksft_set_plan(2);
+	test_statmount_mnt_ns_id();
+	test_listmount_ns();
+
+	if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
+		ksft_exit_fail();
+	else
+		ksft_exit_pass();
+}