[RFC][PATCH 1/5] fanotify: add support for watching the namespaces tree

[Amir Goldstein <amir73il@gmail.com>]

Introduce FAN_MARK_USERNS type to mark a user namespace object
from nsfs path.

Support two events FAN_CREATE and FAN_DELETE to report creation
and tear down of namespaces owned by the marked userns.

Introduce FAN_REPORT_NSID to report the self and owner nsid of
the created or torn down namespace.

At this time, an fanotify group initialized with flags
FAN_REPORT_MNT|FAN_REPORT_NSID, may add marks on both userns
and mntns objects to mix mount and namespace events, but the same
group cannot also request filesystem events with file handles
(e.g. FAN_REPORT_FID).

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c      | 32 ++++++++++++++
 fs/notify/fanotify/fanotify.h      | 19 ++++++++
 fs/notify/fanotify/fanotify_user.c | 71 +++++++++++++++++++++++++-----
 fs/notify/fdinfo.c                 |  9 +++-
 fs/notify/fsnotify.c               | 28 +++++++++++-
 fs/notify/fsnotify.h               |  7 +++
 fs/notify/mark.c                   |  7 +++
 fs/nsfs.c                          | 21 +++++++++
 include/linux/fanotify.h           | 14 ++++--
 include/linux/fsnotify_backend.h   | 22 +++++++++
 include/linux/proc_fs.h            |  2 +
 include/linux/user_namespace.h     |  6 +++
 include/uapi/linux/fanotify.h      |  9 ++++
 kernel/nscommon.c                  | 46 +++++++++++++++++++
 14 files changed, 276 insertions(+), 17 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index bfe884d624e7b..3818b4d53dcad 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -168,6 +168,8 @@ static bool fanotify_should_merge(struct fanotify_event *old,
 						  FANOTIFY_EE(new));
 	case FANOTIFY_EVENT_TYPE_MNT:
 		return false;
+	case FANOTIFY_EVENT_TYPE_NS:
+		return false;
 	default:
 		WARN_ON_ONCE(1);
 	}
@@ -317,6 +319,9 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 	if (FAN_GROUP_FLAG(group, FAN_REPORT_MNT)) {
 		if (data_type != FSNOTIFY_EVENT_MNT)
 			return 0;
+	} else if (FAN_GROUP_FLAG(group, FAN_REPORT_NSID)) {
+		if (data_type != FSNOTIFY_EVENT_NS)
+			return 0;
 	} else if (!fid_mode) {
 		/* Do we have path to open a file descriptor? */
 		if (!path)
@@ -582,6 +587,22 @@ static struct fanotify_event *fanotify_alloc_mnt_event(u64 mnt_id, gfp_t gfp)
 	return &pevent->fae;
 }
 
+static struct fanotify_event *fanotify_alloc_ns_event(const struct fsnotify_ns *ns_data,
+						      gfp_t gfp)
+{
+	struct fanotify_ns_event *pevent;
+
+	pevent = kmem_cache_alloc(fanotify_ns_event_cachep, gfp);
+	if (!pevent)
+		return NULL;
+
+	pevent->fae.type = FANOTIFY_EVENT_TYPE_NS;
+	pevent->self_nsid = ns_data->self_nsid;
+	pevent->owner_nsid = ns_data->owner_nsid;
+
+	return &pevent->fae;
+}
+
 static struct fanotify_event *fanotify_alloc_perm_event(const void *data,
 							int data_type,
 							gfp_t gfp)
@@ -755,6 +776,7 @@ static struct fanotify_event *fanotify_alloc_event(
 	struct inode *id = fanotify_fid_inode(mask, data, data_type, dir,
 					      fid_mode);
 	struct inode *dirid = fanotify_dfid_inode(mask, data, data_type, dir);
+	const struct fsnotify_ns *ns_data = fsnotify_data_ns(data, data_type);
 	const struct path *path = fsnotify_data_path(data, data_type);
 	u64 mnt_id = fsnotify_data_mnt_id(data, data_type);
 	struct mem_cgroup *old_memcg;
@@ -856,6 +878,8 @@ static struct fanotify_event *fanotify_alloc_event(
 		event = fanotify_alloc_path_event(path, &hash, gfp);
 	} else if (mnt_id) {
 		event = fanotify_alloc_mnt_event(mnt_id, gfp);
+	} else if (ns_data) {
+		event = fanotify_alloc_ns_event(ns_data, gfp);
 	} else {
 		WARN_ON_ONCE(1);
 	}
@@ -1064,6 +1088,11 @@ static void fanotify_free_mnt_event(struct fanotify_event *event)
 	kmem_cache_free(fanotify_mnt_event_cachep, FANOTIFY_ME(event));
 }
 
+static void fanotify_free_ns_event(struct fanotify_event *event)
+{
+	kmem_cache_free(fanotify_ns_event_cachep, FANOTIFY_NSE(event));
+}
+
 static void fanotify_free_event(struct fsnotify_group *group,
 				struct fsnotify_event *fsn_event)
 {
@@ -1093,6 +1122,9 @@ static void fanotify_free_event(struct fsnotify_group *group,
 	case FANOTIFY_EVENT_TYPE_MNT:
 		fanotify_free_mnt_event(event);
 		break;
+	case FANOTIFY_EVENT_TYPE_NS:
+		fanotify_free_ns_event(event);
+		break;
 	default:
 		WARN_ON_ONCE(1);
 	}
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 39e60218df7ce..2eaac302ccac0 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -10,6 +10,7 @@ extern struct kmem_cache *fanotify_fid_event_cachep;
 extern struct kmem_cache *fanotify_path_event_cachep;
 extern struct kmem_cache *fanotify_perm_event_cachep;
 extern struct kmem_cache *fanotify_mnt_event_cachep;
+extern struct kmem_cache *fanotify_ns_event_cachep;
 
 /* Possible states of the permission event */
 enum {
@@ -245,6 +246,7 @@ enum fanotify_event_type {
 	FANOTIFY_EVENT_TYPE_OVERFLOW, /* struct fanotify_event */
 	FANOTIFY_EVENT_TYPE_FS_ERROR, /* struct fanotify_error_event */
 	FANOTIFY_EVENT_TYPE_MNT,
+	FANOTIFY_EVENT_TYPE_NS,
 	__FANOTIFY_EVENT_TYPE_NUM
 };
 
@@ -415,6 +417,12 @@ struct fanotify_mnt_event {
 	u64 mnt_id;
 };
 
+struct fanotify_ns_event {
+	struct fanotify_event fae;
+	u64 self_nsid;
+	u64 owner_nsid;
+};
+
 static inline struct fanotify_path_event *
 FANOTIFY_PE(struct fanotify_event *event)
 {
@@ -427,6 +435,12 @@ FANOTIFY_ME(struct fanotify_event *event)
 	return container_of(event, struct fanotify_mnt_event, fae);
 }
 
+static inline struct fanotify_ns_event *
+FANOTIFY_NSE(struct fanotify_event *event)
+{
+	return container_of(event, struct fanotify_ns_event, fae);
+}
+
 /*
  * Structure for permission fanotify events. It gets allocated and freed in
  * fanotify_handle_event() since we wait there for user response. When the
@@ -485,6 +499,11 @@ static inline bool fanotify_is_mnt_event(u32 mask)
 	return mask & (FAN_MNT_ATTACH | FAN_MNT_DETACH);
 }
 
+static inline bool fanotify_is_ns_event(const struct fanotify_event *event)
+{
+	return event->type == FANOTIFY_EVENT_TYPE_NS;
+}
+
 static inline const struct path *fanotify_event_path(struct fanotify_event *event)
 {
 	if (event->type == FANOTIFY_EVENT_TYPE_PATH)
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index ae904451dfc09..126069101669a 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -19,6 +19,7 @@
 #include <linux/memcontrol.h>
 #include <linux/statfs.h>
 #include <linux/exportfs.h>
+#include <linux/proc_fs.h>
 
 #include <asm/ioctls.h>
 
@@ -208,6 +209,7 @@ struct kmem_cache *fanotify_fid_event_cachep __ro_after_init;
 struct kmem_cache *fanotify_path_event_cachep __ro_after_init;
 struct kmem_cache *fanotify_perm_event_cachep __ro_after_init;
 struct kmem_cache *fanotify_mnt_event_cachep __ro_after_init;
+struct kmem_cache *fanotify_ns_event_cachep __ro_after_init;
 
 #define FANOTIFY_EVENT_ALIGN 4
 #define FANOTIFY_FID_INFO_HDR_LEN \
@@ -220,6 +222,8 @@ struct kmem_cache *fanotify_mnt_event_cachep __ro_after_init;
 	(sizeof(struct fanotify_event_info_range))
 #define FANOTIFY_MNT_INFO_LEN \
 	(sizeof(struct fanotify_event_info_mnt))
+#define FANOTIFY_NS_INFO_LEN \
+	(sizeof(struct fanotify_event_info_ns))
 
 static int fanotify_fid_info_len(int fh_len, int name_len)
 {
@@ -277,6 +281,8 @@ static size_t fanotify_event_len(unsigned int info_mode,
 	}
 	if (fanotify_is_mnt_event(event->mask))
 		event_len += FANOTIFY_MNT_INFO_LEN;
+	if (fanotify_is_ns_event(event))
+		event_len += FANOTIFY_NS_INFO_LEN;
 
 	if (info_mode & FAN_REPORT_PIDFD)
 		event_len += FANOTIFY_PIDFD_INFO_LEN;
@@ -523,6 +529,26 @@ static size_t copy_mnt_info_to_user(struct fanotify_event *event,
 	return info.hdr.len;
 }
 
+static size_t copy_ns_info_to_user(struct fanotify_event *event,
+				   char __user *buf, int count)
+{
+	struct fanotify_event_info_ns info = { };
+
+	info.hdr.info_type = FAN_EVENT_INFO_TYPE_NS;
+	info.hdr.len = sizeof(info);
+
+	if (WARN_ON(count < info.hdr.len))
+		return -EFAULT;
+
+	info.self_nsid  = FANOTIFY_NSE(event)->self_nsid;
+	info.owner_nsid = FANOTIFY_NSE(event)->owner_nsid;
+
+	if (copy_to_user(buf, &info, sizeof(info)))
+		return -EFAULT;
+
+	return info.hdr.len;
+}
+
 static size_t copy_error_info_to_user(struct fanotify_event *event,
 				      char __user *buf, int count)
 {
@@ -827,6 +853,15 @@ static int copy_info_records_to_user(struct fanotify_event *event,
 		total_bytes += ret;
 	}
 
+	if (fanotify_is_ns_event(event)) {
+		ret = copy_ns_info_to_user(event, buf, count);
+		if (ret < 0)
+			return ret;
+		buf += ret;
+		count -= ret;
+		total_bytes += ret;
+	}
+
 	return total_bytes;
 }
 
@@ -1604,11 +1639,11 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 	/*
 	 * An unprivileged user can setup an fanotify group with limited
 	 * functionality - an unprivileged group is limited to notification
-	 * events with file handles or mount ids and it cannot use unlimited
+	 * events with file handles or mount/ns ids and it cannot use unlimited
 	 * queue/marks.
 	 */
 	if (((flags & FANOTIFY_ADMIN_INIT_FLAGS) ||
-	     !(flags & (FANOTIFY_FID_BITS | FAN_REPORT_MNT))) &&
+	     !(flags & (FANOTIFY_FID_BITS | FAN_REPORT_MNT | FAN_REPORT_NSID))) &&
 	    !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
@@ -1636,8 +1671,8 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 	if ((flags & FAN_REPORT_PIDFD) && (flags & FAN_REPORT_TID))
 		return -EINVAL;
 
-	/* Don't allow mixing mnt events with inode events for now */
-	if (flags & FAN_REPORT_MNT) {
+	/* Don't allow mixing mnt/ns events with inode events for now */
+	if (flags & (FAN_REPORT_MNT | FAN_REPORT_NSID)) {
 		if (class != FAN_CLASS_NOTIF)
 			return -EINVAL;
 		if (flags & (FANOTIFY_FID_BITS | FAN_REPORT_FD_ERROR))
@@ -1913,6 +1948,9 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 	case FAN_MARK_MNTNS:
 		obj_type = FSNOTIFY_OBJ_TYPE_MNTNS;
 		break;
+	case FAN_MARK_USERNS:
+		obj_type = FSNOTIFY_OBJ_TYPE_USERNS;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -1960,16 +1998,22 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 		return -EINVAL;
 	group = fd_file(f)->private_data;
 
-	/* Only report mount events on mnt namespace */
-	if (FAN_GROUP_FLAG(group, FAN_REPORT_MNT)) {
+	/* Only report mount events on mnt namespace mark */
+	if (mark_type == FAN_MARK_MNTNS) {
 		if (mask & ~FANOTIFY_MOUNT_EVENTS)
 			return -EINVAL;
-		if (mark_type != FAN_MARK_MNTNS)
+		if (!FAN_GROUP_FLAG(group, FAN_REPORT_MNT))
 			return -EINVAL;
 	} else {
 		if (mask & FANOTIFY_MOUNT_EVENTS)
 			return -EINVAL;
-		if (mark_type == FAN_MARK_MNTNS)
+	}
+
+	/* Only report namespace events on user namespace mark */
+	if (mark_type == FAN_MARK_USERNS) {
+		if (mask & ~FANOTIFY_NS_EVENTS)
+			return -EINVAL;
+		if (!FAN_GROUP_FLAG(group, FAN_REPORT_NSID))
 			return -EINVAL;
 	}
 
@@ -2087,6 +2131,12 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 			goto path_put_and_out;
 		user_ns = mntns->user_ns;
 		obj = mntns;
+	} else if (obj_type == FSNOTIFY_OBJ_TYPE_USERNS) {
+		ret = -EINVAL;
+		user_ns = userns_from_dentry(path.dentry);
+		if (!user_ns)
+			goto path_put_and_out;
+		obj = user_ns;
 	}
 
 	ret = -EPERM;
@@ -2190,8 +2240,8 @@ static int __init fanotify_user_setup(void)
 				     FANOTIFY_DEFAULT_MAX_USER_MARKS);
 
 	BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_GROUP_FLAGS);
-	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 14);
-	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 11);
+	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 15);
+	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 12);
 
 	fanotify_mark_cache = KMEM_CACHE(fanotify_mark,
 					 SLAB_PANIC|SLAB_ACCOUNT);
@@ -2204,6 +2254,7 @@ static int __init fanotify_user_setup(void)
 			KMEM_CACHE(fanotify_perm_event, SLAB_PANIC);
 	}
 	fanotify_mnt_event_cachep = KMEM_CACHE(fanotify_mnt_event, SLAB_PANIC);
+	fanotify_ns_event_cachep = KMEM_CACHE(fanotify_ns_event, SLAB_PANIC);
 
 	fanotify_max_queued_events = FANOTIFY_DEFAULT_MAX_EVENTS;
 	init_user_ns.ucount_max[UCOUNT_FANOTIFY_GROUPS] =
diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c
index 9cc7eb8636437..946cffaf16e18 100644
--- a/fs/notify/fdinfo.c
+++ b/fs/notify/fdinfo.c
@@ -130,8 +130,13 @@ static void fanotify_fdinfo(struct seq_file *m, struct fsnotify_mark *mark)
 	} else if (mark->connector->type == FSNOTIFY_OBJ_TYPE_MNTNS) {
 		struct mnt_namespace *mnt_ns = fsnotify_conn_mntns(mark->connector);
 
-		seq_printf(m, "fanotify mnt_ns:%u mflags:%x mask:%x ignored_mask:%x\n",
-			   mnt_ns->ns.inum, mflags, mark->mask, mark->ignore_mask);
+		seq_printf(m, "fanotify mnt_ns_id:%llu mflags:%x mask:%x ignored_mask:%x\n",
+			   mnt_ns->ns.ns_id, mflags, mark->mask, mark->ignore_mask);
+	} else if (mark->connector->type == FSNOTIFY_OBJ_TYPE_USERNS) {
+		struct user_namespace *userns = fsnotify_conn_userns(mark->connector);
+
+		seq_printf(m, "fanotify user_ns_id:%llu mflags:%x mask:%x ignored_mask:%x\n",
+			   userns->ns.ns_id, mflags, mark->mask, mark->ignore_mask);
 	}
 }
 
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 9995de1710e59..638136c0d6cb9 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -495,6 +495,7 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 	const struct path *path = fsnotify_data_path(data, data_type);
 	struct super_block *sb = fsnotify_data_sb(data, data_type);
 	const struct fsnotify_mnt *mnt_data = fsnotify_data_mnt(data, data_type);
+	const struct fsnotify_ns *ns_data = fsnotify_data_ns(data, data_type);
 	struct fsnotify_sb_info *sbinfo = sb ? fsnotify_sb_info(sb) : NULL;
 	struct fsnotify_iter_info iter_info = {};
 	struct mount *mnt = NULL;
@@ -536,7 +537,8 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 	    (!mnt || !mnt->mnt_fsnotify_marks) &&
 	    (!inode || !inode->i_fsnotify_marks) &&
 	    (!inode2 || !inode2->i_fsnotify_marks) &&
-	    (!mnt_data || !mnt_data->ns->n_fsnotify_marks))
+	    (!mnt_data || !mnt_data->ns->n_fsnotify_marks) &&
+	    (!ns_data || !ns_data->userns->n_fsnotify_marks))
 		return 0;
 
 	if (sb)
@@ -549,6 +551,8 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 		marks_mask |= READ_ONCE(inode2->i_fsnotify_mask);
 	if (mnt_data)
 		marks_mask |= READ_ONCE(mnt_data->ns->n_fsnotify_mask);
+	if (ns_data)
+		marks_mask |= READ_ONCE(ns_data->userns->n_fsnotify_mask);
 
 	/*
 	 * If this is a modify event we may need to clear some ignore masks.
@@ -582,6 +586,10 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 		iter_info.marks[FSNOTIFY_ITER_TYPE_MNTNS] =
 			fsnotify_first_mark(&mnt_data->ns->n_fsnotify_marks);
 	}
+	if (ns_data) {
+		iter_info.marks[FSNOTIFY_ITER_TYPE_USERNS] =
+			fsnotify_first_mark(&ns_data->userns->n_fsnotify_marks);
+	}
 
 	/*
 	 * We need to merge inode/vfsmount/sb mark lists so that e.g. inode mark
@@ -711,6 +719,24 @@ void fsnotify_mnt(__u32 mask, struct mnt_namespace *ns, struct vfsmount *mnt)
 	fsnotify(mask, &data, FSNOTIFY_EVENT_MNT, NULL, NULL, NULL, 0);
 }
 
+void fsnotify_ns(__u32 mask, struct user_namespace *userns,
+		 u64 self_nsid, u64 owner_nsid)
+{
+	struct fsnotify_ns data = {
+		.userns = userns,
+		.self_nsid = self_nsid,
+		.owner_nsid = owner_nsid,
+	};
+
+	if (WARN_ON_ONCE(!userns))
+		return;
+
+	if (!READ_ONCE(userns->n_fsnotify_marks))
+		return;
+
+	fsnotify(mask, &data, FSNOTIFY_EVENT_NS, NULL, NULL, NULL, 0);
+}
+
 static __init int fsnotify_init(void)
 {
 	int ret;
diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h
index 58c7bb25e5718..f58c69de7f067 100644
--- a/fs/notify/fsnotify.h
+++ b/fs/notify/fsnotify.h
@@ -6,6 +6,7 @@
 #include <linux/fsnotify.h>
 #include <linux/srcu.h>
 #include <linux/types.h>
+#include <linux/user_namespace.h>
 
 #include "../mount.h"
 
@@ -39,6 +40,12 @@ static inline struct mnt_namespace *fsnotify_conn_mntns(
 	return conn->obj;
 }
 
+static inline struct user_namespace *fsnotify_conn_userns(
+				struct fsnotify_mark_connector *conn)
+{
+	return conn->obj;
+}
+
 static inline struct super_block *fsnotify_object_sb(void *obj,
 			enum fsnotify_obj_type obj_type)
 {
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index c2ed5b11b0fe6..4086b37637cbe 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -74,6 +74,7 @@
 #include <linux/atomic.h>
 
 #include <linux/fsnotify_backend.h>
+#include <linux/user_namespace.h>
 #include "fsnotify.h"
 
 #define FSNOTIFY_REAPER_DELAY	(1)	/* 1 jiffy */
@@ -110,6 +111,8 @@ static fsnotify_connp_t *fsnotify_object_connp(void *obj,
 		return fsnotify_sb_marks(obj);
 	case FSNOTIFY_OBJ_TYPE_MNTNS:
 		return &((struct mnt_namespace *)obj)->n_fsnotify_marks;
+	case FSNOTIFY_OBJ_TYPE_USERNS:
+		return &((struct user_namespace *)obj)->n_fsnotify_marks;
 	default:
 		return NULL;
 	}
@@ -125,6 +128,8 @@ static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn)
 		return &fsnotify_conn_sb(conn)->s_fsnotify_mask;
 	else if (conn->type == FSNOTIFY_OBJ_TYPE_MNTNS)
 		return &fsnotify_conn_mntns(conn)->n_fsnotify_mask;
+	else if (conn->type == FSNOTIFY_OBJ_TYPE_USERNS)
+		return &fsnotify_conn_userns(conn)->n_fsnotify_mask;
 	return NULL;
 }
 
@@ -356,6 +361,8 @@ static void *fsnotify_detach_connector_from_object(
 		fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
 	} else if (conn->type == FSNOTIFY_OBJ_TYPE_MNTNS) {
 		fsnotify_conn_mntns(conn)->n_fsnotify_mask = 0;
+	} else if (conn->type == FSNOTIFY_OBJ_TYPE_USERNS) {
+		fsnotify_conn_userns(conn)->n_fsnotify_mask = 0;
 	}
 
 	rcu_assign_pointer(*connp, NULL);
diff --git a/fs/nsfs.c b/fs/nsfs.c
index c215878d55e87..ace17de243f45 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -387,6 +387,27 @@ bool proc_ns_file(const struct file *file)
 	return file->f_op == &ns_file_operations;
 }
 
+/**
+ * userns_from_dentry() - Return the user_namespace referenced by an nsfs dentry.
+ * @dentry: dentry of an open nsfs file
+ *
+ * Returns the user_namespace if @dentry is an nsfs file for a user namespace,
+ * NULL otherwise.  The caller is responsible for ensuring the returned pointer
+ * remains valid (e.g. by holding a reference to the dentry).
+ */
+struct user_namespace *userns_from_dentry(struct dentry *dentry)
+{
+	struct inode *inode = d_inode(dentry);
+	struct ns_common *ns;
+
+	if (!inode || inode->i_sb->s_magic != NSFS_MAGIC)
+		return NULL;
+	ns = get_proc_ns(inode);
+	if (!ns || ns->ns_type != CLONE_NEWUSER)
+		return NULL;
+	return to_user_ns(ns);
+}
+
 /**
  * ns_match() - Returns true if current namespace matches dev/ino provided.
  * @ns: current namespace
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 879cff5eccd4e..279082ae40fe2 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -25,7 +25,8 @@
 
 #define FANOTIFY_FID_BITS	(FAN_REPORT_DFID_NAME_TARGET)
 
-#define FANOTIFY_INFO_MODES	(FANOTIFY_FID_BITS | FAN_REPORT_PIDFD | FAN_REPORT_MNT)
+#define FANOTIFY_INFO_MODES	(FANOTIFY_FID_BITS | FAN_REPORT_PIDFD | FAN_REPORT_MNT | \
+				 FAN_REPORT_NSID)
 
 /*
  * fanotify_init() flags that require CAP_SYS_ADMIN.
@@ -47,8 +48,9 @@
  * so one of the flags for reporting file handles is required.
  */
 #define FANOTIFY_USER_INIT_FLAGS	(FAN_CLASS_NOTIF | \
-					 FANOTIFY_FID_BITS | FAN_REPORT_MNT | \
-					 FAN_CLOEXEC | FAN_NONBLOCK)
+				 FANOTIFY_FID_BITS | FAN_REPORT_MNT | \
+				 FAN_REPORT_NSID | \
+				 FAN_CLOEXEC | FAN_NONBLOCK)
 
 #define FANOTIFY_INIT_FLAGS	(FANOTIFY_ADMIN_INIT_FLAGS | \
 				 FANOTIFY_USER_INIT_FLAGS)
@@ -58,7 +60,8 @@
 #define FANOTIFY_INTERNAL_GROUP_FLAGS	(FANOTIFY_UNPRIV)
 
 #define FANOTIFY_MARK_TYPE_BITS	(FAN_MARK_INODE | FAN_MARK_MOUNT | \
-				 FAN_MARK_FILESYSTEM | FAN_MARK_MNTNS)
+				 FAN_MARK_FILESYSTEM | FAN_MARK_MNTNS | \
+				 FAN_MARK_USERNS)
 
 #define FANOTIFY_MARK_CMD_BITS	(FAN_MARK_ADD | FAN_MARK_REMOVE | \
 				 FAN_MARK_FLUSH)
@@ -111,6 +114,9 @@
 
 #define FANOTIFY_MOUNT_EVENTS	(FAN_MNT_ATTACH | FAN_MNT_DETACH)
 
+/* Events that can be reported with data type FSNOTIFY_EVENT_NS */
+#define FANOTIFY_NS_EVENTS	(FAN_CREATE | FAN_DELETE)
+
 /* Events that user can request to be notified on */
 #define FANOTIFY_EVENTS		(FANOTIFY_PATH_EVENTS | \
 				 FANOTIFY_INODE_EVENTS | \
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 95985400d3d8e..2145d2f4262db 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -310,6 +310,7 @@ enum fsnotify_data_type {
 	FSNOTIFY_EVENT_INODE,
 	FSNOTIFY_EVENT_DENTRY,
 	FSNOTIFY_EVENT_MNT,
+	FSNOTIFY_EVENT_NS,
 	FSNOTIFY_EVENT_ERROR,
 };
 
@@ -335,6 +336,12 @@ struct fsnotify_mnt {
 	u64 mnt_id;
 };
 
+struct fsnotify_ns {
+	const struct user_namespace *userns;
+	u64 self_nsid;
+	u64 owner_nsid;
+};
+
 static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
 {
 	switch (data_type) {
@@ -411,6 +418,17 @@ static inline const struct fsnotify_mnt *fsnotify_data_mnt(const void *data,
 	}
 }
 
+static inline const struct fsnotify_ns *fsnotify_data_ns(const void *data,
+							 int data_type)
+{
+	switch (data_type) {
+	case FSNOTIFY_EVENT_NS:
+		return data;
+	default:
+		return NULL;
+	}
+}
+
 static inline u64 fsnotify_data_mnt_id(const void *data, int data_type)
 {
 	const struct fsnotify_mnt *mnt_data = fsnotify_data_mnt(data, data_type);
@@ -456,6 +474,7 @@ enum fsnotify_iter_type {
 	FSNOTIFY_ITER_TYPE_PARENT,
 	FSNOTIFY_ITER_TYPE_INODE2,
 	FSNOTIFY_ITER_TYPE_MNTNS,
+	FSNOTIFY_ITER_TYPE_USERNS,
 	FSNOTIFY_ITER_TYPE_COUNT
 };
 
@@ -466,6 +485,7 @@ enum fsnotify_obj_type {
 	FSNOTIFY_OBJ_TYPE_VFSMOUNT,
 	FSNOTIFY_OBJ_TYPE_SB,
 	FSNOTIFY_OBJ_TYPE_MNTNS,
+	FSNOTIFY_OBJ_TYPE_USERNS,
 	FSNOTIFY_OBJ_TYPE_COUNT,
 	FSNOTIFY_OBJ_TYPE_DETACHED = FSNOTIFY_OBJ_TYPE_COUNT
 };
@@ -657,6 +677,8 @@ extern void __fsnotify_mntns_delete(struct mnt_namespace *mntns);
 extern void fsnotify_sb_free(struct super_block *sb);
 extern u32 fsnotify_get_cookie(void);
 extern void fsnotify_mnt(__u32 mask, struct mnt_namespace *ns, struct vfsmount *mnt);
+extern void fsnotify_ns(__u32 mask, struct user_namespace *userns,
+			u64 self_nsid, u64 owner_nsid);
 
 static inline __u32 fsnotify_parent_needed_mask(__u32 mask)
 {
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 19d1c5e5f3350..3b7d2bc88ae6c 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -248,4 +248,6 @@ static inline struct pid_namespace *proc_pid_ns(struct super_block *sb)
 
 bool proc_ns_file(const struct file *file);
 
+struct user_namespace *userns_from_dentry(struct dentry *dentry);
+
 #endif /* _LINUX_PROC_FS_H */
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9c3be157397e0..7ff8420495308 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -13,6 +13,8 @@
 #include <linux/sysctl.h>
 #include <linux/err.h>
 
+struct fsnotify_mark_connector;
+
 #define UID_GID_MAP_MAX_BASE_EXTENTS 5
 #define UID_GID_MAP_MAX_EXTENTS 340
 
@@ -86,6 +88,10 @@ struct user_namespace {
 	/* parent_could_setfcap: true if the creator if this ns had CAP_SETFCAP
 	 * in its effective capability set at the child ns creation time. */
 	bool			parent_could_setfcap;
+#ifdef CONFIG_FSNOTIFY
+	__u32 n_fsnotify_mask;
+	struct fsnotify_mark_connector __rcu *n_fsnotify_marks;
+#endif
 
 #ifdef CONFIG_KEYS
 	/* List of joinable keyrings in this namespace.  Modification access of
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index e710967c7c263..6b4f470ee7e01 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -67,6 +67,7 @@
 #define FAN_REPORT_TARGET_FID	0x00001000	/* Report dirent target id  */
 #define FAN_REPORT_FD_ERROR	0x00002000	/* event->fd can report error */
 #define FAN_REPORT_MNT		0x00004000	/* Report mount events */
+#define FAN_REPORT_NSID		0x00008000	/* Report namespace events */
 
 /* Convenience macro - FAN_REPORT_NAME requires FAN_REPORT_DIR_FID */
 #define FAN_REPORT_DFID_NAME	(FAN_REPORT_DIR_FID | FAN_REPORT_NAME)
@@ -98,6 +99,7 @@
 #define FAN_MARK_MOUNT		0x00000010
 #define FAN_MARK_FILESYSTEM	0x00000100
 #define FAN_MARK_MNTNS		0x00000110
+#define FAN_MARK_USERNS		0x00001000
 
 /*
  * Convenience macro - FAN_MARK_IGNORE requires FAN_MARK_IGNORED_SURV_MODIFY
@@ -152,6 +154,7 @@ struct fanotify_event_metadata {
 #define FAN_EVENT_INFO_TYPE_ERROR	5
 #define FAN_EVENT_INFO_TYPE_RANGE	6
 #define FAN_EVENT_INFO_TYPE_MNT		7
+#define FAN_EVENT_INFO_TYPE_NS		8
 
 /* Special info types for FAN_RENAME */
 #define FAN_EVENT_INFO_TYPE_OLD_DFID_NAME	10
@@ -210,6 +213,12 @@ struct fanotify_event_info_mnt {
 	__u64 mnt_id;
 };
 
+struct fanotify_event_info_ns {
+	struct fanotify_event_info_header hdr;
+	__u64 self_nsid;	/* ns_id of the namespace */
+	__u64 owner_nsid;	/* ns_id of its owning user namespace */
+};
+
 /*
  * User space may need to record additional information about its decision.
  * The extra information type records what kind of information is included.
diff --git a/kernel/nscommon.c b/kernel/nscommon.c
index 3166c1fd844af..a6fdacb394ea7 100644
--- a/kernel/nscommon.c
+++ b/kernel/nscommon.c
@@ -6,6 +6,7 @@
 #include <linux/proc_ns.h>
 #include <linux/user_namespace.h>
 #include <linux/vfsdebug.h>
+#include <linux/fsnotify_backend.h>
 
 #ifdef CONFIG_DEBUG_VFS
 static void ns_debug(struct ns_common *ns, const struct proc_ns_operations *ops)
@@ -111,6 +112,43 @@ struct ns_common *__must_check ns_owner(struct ns_common *ns)
 	return to_ns_common(owner);
 }
 
+/*
+ * Return the owning user_namespace of @ns, including init_user_ns.
+ * Unlike ns_owner(), which returns NULL for namespaces owned by
+ * init_user_ns (to serve as a propagation terminator), this gives us
+ * the real owner for notification routing.
+ */
+static struct user_namespace *ns_direct_owner(struct ns_common *ns)
+{
+	if (unlikely(!ns->ops || !ns->ops->owner))
+		return NULL;
+	return ns->ops->owner(ns);
+}
+
+static void ns_common_notify(__u32 mask, struct ns_common *ns)
+{
+	struct user_namespace *owner_userns;
+
+	if (!IS_ENABLED(CONFIG_FSNOTIFY))
+		return;
+
+	owner_userns = ns_direct_owner(ns);
+	if (!owner_userns)
+		return;
+
+#ifdef CONFIG_FSNOTIFY
+	/*
+	 * READ_ONCE macro expansion does not understand that this code
+	 * is not reachable without CONFIG_FSNOTIFY.
+	 */
+	if (!READ_ONCE(owner_userns->n_fsnotify_marks))
+		return;
+#endif
+
+	fsnotify_ns(mask, owner_userns, ns->ns_id,
+		    to_ns_common(owner_userns)->ns_id);
+}
+
 /*
  * The active reference count works by having each namespace that gets
  * created take a single active reference on its owning user namespace.
@@ -172,6 +210,8 @@ void __ns_ref_active_put(struct ns_common *ns)
 		return;
 	}
 
+	ns_common_notify(FS_DELETE, ns);
+
 	VFS_WARN_ON_ONCE(is_ns_init_id(ns));
 	VFS_WARN_ON_ONCE(!__ns_ref_read(ns));
 
@@ -184,6 +224,8 @@ void __ns_ref_active_put(struct ns_common *ns)
 			VFS_WARN_ON_ONCE(__ns_ref_active_read(ns) < 0);
 			return;
 		}
+
+		ns_common_notify(FS_DELETE, ns);
 	}
 }
 
@@ -293,6 +335,8 @@ void __ns_ref_active_get(struct ns_common *ns)
 	if (likely(prev))
 		return;
 
+	ns_common_notify(FS_CREATE, ns);
+
 	/*
 	 * We did resurrect it. Walk the ownership hierarchy upwards
 	 * until we found an owning user namespace that is active.
@@ -307,6 +351,8 @@ void __ns_ref_active_get(struct ns_common *ns)
 		VFS_WARN_ON_ONCE(prev < 0);
 		if (likely(prev))
 			return;
+
+		ns_common_notify(FS_CREATE, ns);
 	}
 }
 
-- 
2.53.0