diff --git a/fs/namei.c b/fs/namei.c
index a9ca46e4f82c..eaf07f87cba5 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -641,6 +641,14 @@ static bool legitimize_links(struct nameidata *nd)
 
 static bool legitimize_root(struct nameidata *nd)
 {
+	/*
+	 * For scoped-lookups (where nd->root has been zeroed), we need to
+	 * restart the whole lookup from scratch -- because set_root() is wrong
+	 * for these lookups (nd->dfd is the root, not the filesystem root).
+	 */
+	if (!nd->root.mnt && (nd->flags & LOOKUP_IS_SCOPED))
+		return false;
+	/* Nothing to do if nd->root is zero or is managed by the VFS user. */
 	if (!nd->root.mnt || (nd->flags & LOOKUP_ROOT))
 		return true;
 	nd->flags |= LOOKUP_ROOT_GRABBED;
@@ -776,12 +784,37 @@ static int complete_walk(struct nameidata *nd)
 	int status;
 
 	if (nd->flags & LOOKUP_RCU) {
-		if (!(nd->flags & LOOKUP_ROOT))
+		/*
+		 * We don't want to zero nd->root for scoped-lookups or
+		 * externally-managed nd->root.
+		 */
+		if (!(nd->flags & (LOOKUP_ROOT | LOOKUP_IS_SCOPED)))
 			nd->root.mnt = NULL;
 		if (unlikely(unlazy_walk(nd)))
 			return -ECHILD;
 	}
 
+	if (unlikely(nd->flags & LOOKUP_IS_SCOPED)) {
+		/*
+		 * While the guarantee of LOOKUP_IS_SCOPED is (roughly) "don't
+		 * ever step outside the root during lookup" and should already
+		 * be guaranteed by the rest of namei, we want to avoid a namei
+		 * BUG resulting in userspace being given a path that was not
+		 * scoped within the root at some point during the lookup.
+		 *
+		 * So, do a final sanity-check to make sure that in the
+		 * worst-case scenario (a complete bypass of LOOKUP_IS_SCOPED)
+		 * we won't silently return an fd completely outside of the
+		 * requested root to userspace.
+		 *
+		 * Userspace could move the path outside the root after this
+		 * check, but as discussed elsewhere this is not a concern (the
+		 * resolved file was inside the root at some point).
+		 */
+		if (!path_is_under(&nd->path, &nd->root))
+			return -EXDEV;
+	}
+
 	if (likely(!(nd->flags & LOOKUP_JUMPED)))
 		return 0;
 
@@ -802,6 +835,14 @@ static int set_root(struct nameidata *nd)
 {
 	struct fs_struct *fs = current->fs;
 
+	/*
+	 * Jumping to the real root in a scoped-lookup is a BUG in namei, but we
+	 * still have to ensure it doesn't happen because it will cause a breakout
+	 * from the dirfd.
+	 */
+	if (WARN_ON(nd->flags & LOOKUP_IS_SCOPED))
+		return -ENOTRECOVERABLE;
+
 	if (nd->flags & LOOKUP_RCU) {
 		unsigned seq;
 
@@ -838,6 +879,8 @@ static inline void path_to_nameidata(const struct path *path,
 
 static int nd_jump_root(struct nameidata *nd)
 {
+	if (unlikely(nd->flags & LOOKUP_BENEATH))
+		return -EXDEV;
 	if (unlikely(nd->flags & LOOKUP_NO_XDEV)) {
 		/* Absolute path arguments to path_init() are allowed. */
 		if (nd->path.mnt != NULL && nd->path.mnt != nd->root.mnt)
@@ -883,6 +926,9 @@ int nd_jump_link(struct path *path)
 		if (nd->path.mnt != path->mnt)
 			goto err;
 	}
+	/* Not currently safe for scoped-lookups. */
+	if (unlikely(nd->flags & LOOKUP_IS_SCOPED))
+		goto err;
 
 	path_put(&nd->path);
 	nd->path = *path;
@@ -1385,8 +1431,11 @@ static int follow_dotdot_rcu(struct nameidata *nd)
 	struct inode *inode = nd->inode;
 
 	while (1) {
-		if (path_equal(&nd->path, &nd->root))
+		if (path_equal(&nd->path, &nd->root)) {
+			if (unlikely(nd->flags & LOOKUP_BENEATH))
+				return -ECHILD;
 			break;
+		}
 		if (nd->path.dentry != nd->path.mnt->mnt_root) {
 			struct dentry *old = nd->path.dentry;
 			struct dentry *parent = old->d_parent;
@@ -1516,9 +1565,12 @@ static int path_parent_directory(struct path *path)
 
 static int follow_dotdot(struct nameidata *nd)
 {
-	while(1) {
-		if (path_equal(&nd->path, &nd->root))
+	while (1) {
+		if (path_equal(&nd->path, &nd->root)) {
+			if (unlikely(nd->flags & LOOKUP_BENEATH))
+				return -EXDEV;
 			break;
+		}
 		if (nd->path.dentry != nd->path.mnt->mnt_root) {
 			int ret = path_parent_directory(&nd->path);
 			if (ret)
@@ -1741,6 +1793,13 @@ static inline int handle_dots(struct nameidata *nd, int type)
 	if (type == LAST_DOTDOT) {
 		int error = 0;
 
+		/*
+		 * Scoped-lookup flags resolving ".." is not currently safe --
+		 * races can cause our parent to have moved outside of the root
+		 * and us to skip over it.
+		 */
+		if (unlikely(nd->flags & LOOKUP_IS_SCOPED))
+			return -EXDEV;
 		if (!nd->root.mnt) {
 			error = set_root(nd);
 			if (error)
@@ -2258,7 +2317,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
 			get_fs_pwd(current->fs, &nd->path);
 			nd->inode = nd->path.dentry->d_inode;
 		}
-		return s;
 	} else {
 		/* Caller must check execute permissions on the starting path component */
 		struct fd f = fdget_raw(nd->dfd);
@@ -2283,8 +2341,18 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
 			nd->inode = nd->path.dentry->d_inode;
 		}
 		fdput(f);
-		return s;
 	}
+	/* For scoped-lookups we need to set the root to the dirfd as well. */
+	if (flags & LOOKUP_IS_SCOPED) {
+		nd->root = nd->path;
+		if (flags & LOOKUP_RCU) {
+			nd->root_seq = nd->seq;
+		} else {
+			path_get(&nd->root);
+			nd->flags |= LOOKUP_ROOT_GRABBED;
+		}
+	}
+	return s;
 }
 
 static const char *trailing_symlink(struct nameidata *nd)
diff --git a/include/linux/namei.h b/include/linux/namei.h
index edb4562b5c4e..d2a98083be77 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_NAMEI_H
 #define _LINUX_NAMEI_H
 
+#include <linux/fs.h>
 #include <linux/kernel.h>
 #include <linux/path.h>
 #include <linux/fcntl.h>
@@ -43,6 +44,9 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
 #define LOOKUP_NO_SYMLINKS	0x010000 /* No symlink crossing. */
 #define LOOKUP_NO_MAGICLINKS	0x020000 /* No nd_jump_link() crossing. */
 #define LOOKUP_NO_XDEV		0x040000 /* No mountpoint crossing. */
+#define LOOKUP_BENEATH		0x080000 /* No escaping from starting point. */
+/* LOOKUP_* flags which do scope-related checks based on the dirfd. */
+#define LOOKUP_IS_SCOPED LOOKUP_BENEATH
 
 extern int path_pts(struct path *path);