Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 868 insertions, 0 deletions

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
new file mode 100644
index 000000000..9aae20c59
--- /dev/null
+++ b/fs/overlayfs/export.c
@@ -0,0 +1,868 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Overlayfs NFS export support.
+ *
+ * Amir Goldstein <amir73il@gmail.com>
+ *
+ * Copyright (C) 2017-2018 CTERA Networks. All Rights Reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/cred.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/xattr.h>
+#include <linux/exportfs.h>
+#include <linux/ratelimit.h>
+#include "overlayfs.h"
+
+static int ovl_encode_maybe_copy_up(struct dentry *dentry)
+{
+	int err;
+
+	if (ovl_dentry_upper(dentry))
+		return 0;
+
+	err = ovl_copy_up(dentry);
+	if (err) {
+		pr_warn_ratelimited("failed to copy up on encode (%pd2, err=%i)\n",
+				    dentry, err);
+	}
+
+	return err;
+}
+
+/*
+ * Before encoding a non-upper directory file handle from real layer N, we need
+ * to check if it will be possible to reconnect an overlay dentry from the real
+ * lower decoded dentry. This is done by following the overlay ancestry up to a
+ * "layer N connected" ancestor and verifying that all parents along the way are
+ * "layer N connectable". If an ancestor that is NOT "layer N connectable" is
+ * found, we need to copy up an ancestor, which is "layer N connectable", thus
+ * making that ancestor "layer N connected". For example:
+ *
+ * layer 1: /a
+ * layer 2: /a/b/c
+ *
+ * The overlay dentry /a is NOT "layer 2 connectable", because if dir /a is
+ * copied up and renamed, upper dir /a will be indexed by lower dir /a from
+ * layer 1. The dir /a from layer 2 will never be indexed, so the algorithm (*)
+ * in ovl_lookup_real_ancestor() will not be able to lookup a connected overlay
+ * dentry from the connected lower dentry /a/b/c.
+ *
+ * To avoid this problem on decode time, we need to copy up an ancestor of
+ * /a/b/c, which is "layer 2 connectable", on encode time. That ancestor is
+ * /a/b. After copy up (and index) of /a/b, it will become "layer 2 connected"
+ * and when the time comes to decode the file handle from lower dentry /a/b/c,
+ * ovl_lookup_real_ancestor() will find the indexed ancestor /a/b and decoding
+ * a connected overlay dentry will be accomplished.
+ *
+ * (*) the algorithm in ovl_lookup_real_ancestor() can be improved to lookup an
+ * entry /a in the lower layers above layer N and find the indexed dir /a from
+ * layer 1. If that improvement is made, then the check for "layer N connected"
+ * will need to verify there are no redirects in lower layers above N. In the
+ * example above, /a will be "layer 2 connectable". However, if layer 2 dir /a
+ * is a target of a layer 1 redirect, then /a will NOT be "layer 2 connectable":
+ *
+ * layer 1: /A (redirect = /a)
+ * layer 2: /a/b/c
+ */
+
+/* Return the lowest layer for encoding a connectable file handle */
+static int ovl_connectable_layer(struct dentry *dentry)
+{
+	struct ovl_entry *oe = OVL_E(dentry);
+
+	/* We can get overlay root from root of any layer */
+	if (dentry == dentry->d_sb->s_root)
+		return ovl_numlower(oe);
+
+	/*
+	 * If it's an unindexed merge dir, then it's not connectable with any
+	 * lower layer
+	 */
+	if (ovl_dentry_upper(dentry) &&
+	    !ovl_test_flag(OVL_INDEX, d_inode(dentry)))
+		return 0;
+
+	/* We can get upper/overlay path from indexed/lower dentry */
+	return ovl_lowerstack(oe)->layer->idx;
+}
+
+/*
+ * @dentry is "connected" if all ancestors up to root or a "connected" ancestor
+ * have the same uppermost lower layer as the origin's layer. We may need to
+ * copy up a "connectable" ancestor to make it "connected". A "connected" dentry
+ * cannot become non "connected", so cache positive result in dentry flags.
+ *
+ * Return the connected origin layer or < 0 on error.
+ */
+static int ovl_connect_layer(struct dentry *dentry)
+{
+	struct dentry *next, *parent = NULL;
+	struct ovl_entry *oe = OVL_E(dentry);
+	int origin_layer;
+	int err = 0;
+
+	if (WARN_ON(dentry == dentry->d_sb->s_root) ||
+	    WARN_ON(!ovl_dentry_lower(dentry)))
+		return -EIO;
+
+	origin_layer = ovl_lowerstack(oe)->layer->idx;
+	if (ovl_dentry_test_flag(OVL_E_CONNECTED, dentry))
+		return origin_layer;
+
+	/* Find the topmost origin layer connectable ancestor of @dentry */
+	next = dget(dentry);
+	for (;;) {
+		parent = dget_parent(next);
+		if (WARN_ON(parent == next)) {
+			err = -EIO;
+			break;
+		}
+
+		/*
+		 * If @parent is not origin layer connectable, then copy up
+		 * @next which is origin layer connectable and we are done.
+		 */
+		if (ovl_connectable_layer(parent) < origin_layer) {
+			err = ovl_encode_maybe_copy_up(next);
+			break;
+		}
+
+		/* If @parent is connected or indexed we are done */
+		if (ovl_dentry_test_flag(OVL_E_CONNECTED, parent) ||
+		    ovl_test_flag(OVL_INDEX, d_inode(parent)))
+			break;
+
+		dput(next);
+		next = parent;
+	}
+
+	dput(parent);
+	dput(next);
+
+	if (!err)
+		ovl_dentry_set_flag(OVL_E_CONNECTED, dentry);
+
+	return err ?: origin_layer;
+}
+
+/*
+ * We only need to encode origin if there is a chance that the same object was
+ * encoded pre copy up and then we need to stay consistent with the same
+ * encoding also after copy up. If non-pure upper is not indexed, then it was
+ * copied up before NFS export was enabled. In that case we don't need to worry
+ * about staying consistent with pre copy up encoding and we encode an upper
+ * file handle. Overlay root dentry is a private case of non-indexed upper.
+ *
+ * The following table summarizes the different file handle encodings used for
+ * different overlay object types:
+ *
+ *  Object type		| Encoding
+ * --------------------------------
+ *  Pure upper		| U
+ *  Non-indexed upper	| U
+ *  Indexed upper	| L (*)
+ *  Non-upper		| L (*)
+ *
+ * U = upper file handle
+ * L = lower file handle
+ *
+ * (*) Decoding a connected overlay dir from real lower dentry is not always
+ * possible when there are redirects in lower layers and non-indexed merge dirs.
+ * To mitigate those case, we may copy up the lower dir ancestor before encode
+ * of a decodable file handle for non-upper dir.
+ *
+ * Return 0 for upper file handle, > 0 for lower file handle or < 0 on error.
+ */
+static int ovl_check_encode_origin(struct inode *inode)
+{
+	struct ovl_fs *ofs = OVL_FS(inode->i_sb);
+	bool decodable = ofs->config.nfs_export;
+	struct dentry *dentry;
+	int err;
+
+	/* No upper layer? */
+	if (!ovl_upper_mnt(ofs))
+		return 1;
+
+	/* Lower file handle for non-upper non-decodable */
+	if (!ovl_inode_upper(inode) && !decodable)
+		return 1;
+
+	/* Upper file handle for pure upper */
+	if (!ovl_inode_lower(inode))
+		return 0;
+
+	/*
+	 * Root is never indexed, so if there's an upper layer, encode upper for
+	 * root.
+	 */
+	if (inode == d_inode(inode->i_sb->s_root))
+		return 0;
+
+	/*
+	 * Upper decodable file handle for non-indexed upper.
+	 */
+	if (ovl_inode_upper(inode) && decodable &&
+	    !ovl_test_flag(OVL_INDEX, inode))
+		return 0;
+
+	/*
+	 * Decoding a merge dir, whose origin's ancestor is under a redirected
+	 * lower dir or under a non-indexed upper is not always possible.
+	 * ovl_connect_layer() will try to make origin's layer "connected" by
+	 * copying up a "connectable" ancestor.
+	 */
+	if (!decodable || !S_ISDIR(inode->i_mode))
+		return 1;
+
+	dentry = d_find_any_alias(inode);
+	if (!dentry)
+		return -ENOENT;
+
+	err = ovl_connect_layer(dentry);
+	dput(dentry);
+	if (err < 0)
+		return err;
+
+	/* Lower file handle for indexed and non-upper dir/non-dir */
+	return 1;
+}
+
+static int ovl_dentry_to_fid(struct ovl_fs *ofs, struct inode *inode,
+			     u32 *fid, int buflen)
+{
+	struct ovl_fh *fh = NULL;
+	int err, enc_lower;
+	int len;
+
+	/*
+	 * Check if we should encode a lower or upper file handle and maybe
+	 * copy up an ancestor to make lower file handle connectable.
+	 */
+	err = enc_lower = ovl_check_encode_origin(inode);
+	if (enc_lower < 0)
+		goto fail;
+
+	/* Encode an upper or lower file handle */
+	fh = ovl_encode_real_fh(ofs, enc_lower ? ovl_inode_lower(inode) :
+				ovl_inode_upper(inode), !enc_lower);
+	if (IS_ERR(fh))
+		return PTR_ERR(fh);
+
+	len = OVL_FH_LEN(fh);
+	if (len <= buflen)
+		memcpy(fid, fh, len);
+	err = len;
+
+out:
+	kfree(fh);
+	return err;
+
+fail:
+	pr_warn_ratelimited("failed to encode file handle (ino=%llu, err=%i)\n",
+			    inode->i_ino, err);
+	goto out;
+}
+
+static int ovl_encode_fh(struct inode *inode, u32 *fid, int *max_len,
+			 struct inode *parent)
+{
+	struct ovl_fs *ofs = OVL_FS(inode->i_sb);
+	int bytes, buflen = *max_len << 2;
+
+	/* TODO: encode connectable file handles */
+	if (parent)
+		return FILEID_INVALID;
+
+	bytes = ovl_dentry_to_fid(ofs, inode, fid, buflen);
+	if (bytes <= 0)
+		return FILEID_INVALID;
+
+	*max_len = bytes >> 2;
+	if (bytes > buflen)
+		return FILEID_INVALID;
+
+	return OVL_FILEID_V1;
+}
+
+/*
+ * Find or instantiate an overlay dentry from real dentries and index.
+ */
+static struct dentry *ovl_obtain_alias(struct super_block *sb,
+				       struct dentry *upper_alias,
+				       struct ovl_path *lowerpath,
+				       struct dentry *index)
+{
+	struct dentry *lower = lowerpath ? lowerpath->dentry : NULL;
+	struct dentry *upper = upper_alias ?: index;
+	struct inode *inode = NULL;
+	struct ovl_entry *oe;
+	struct ovl_inode_params oip = {
+		.index = index,
+	};
+
+	/* We get overlay directory dentries with ovl_lookup_real() */
+	if (d_is_dir(upper ?: lower))
+		return ERR_PTR(-EIO);
+
+	oe = ovl_alloc_entry(!!lower);
+	if (!oe)
+		return ERR_PTR(-ENOMEM);
+
+	oip.upperdentry = dget(upper);
+	if (lower) {
+		ovl_lowerstack(oe)->dentry = dget(lower);
+		ovl_lowerstack(oe)->layer = lowerpath->layer;
+	}
+	oip.oe = oe;
+	inode = ovl_get_inode(sb, &oip);
+	if (IS_ERR(inode)) {
+		ovl_free_entry(oe);
+		dput(upper);
+		return ERR_CAST(inode);
+	}
+
+	if (upper)
+		ovl_set_flag(OVL_UPPERDATA, inode);
+
+	return d_obtain_alias(inode);
+}
+
+/* Get the upper or lower dentry in stack whose on layer @idx */
+static struct dentry *ovl_dentry_real_at(struct dentry *dentry, int idx)
+{
+	struct ovl_entry *oe = OVL_E(dentry);
+	struct ovl_path *lowerstack = ovl_lowerstack(oe);
+	int i;
+
+	if (!idx)
+		return ovl_dentry_upper(dentry);
+
+	for (i = 0; i < ovl_numlower(oe); i++) {
+		if (lowerstack[i].layer->idx == idx)
+			return lowerstack[i].dentry;
+	}
+
+	return NULL;
+}
+
+/**
+ * ovl_lookup_real_one -  Lookup a child overlay dentry to get an overlay dentry whose real dentry is given
+ * @connected: parent overlay dentry
+ * @real: given child real dentry
+ * @layer: layer in which @real exists
+ *
+ *
+ * Lookup a child overlay dentry in @connected with the same name as the @real
+ * dentry.  Then check that the parent of the result is the real dentry for
+ * @connected, and @real is the real dentry for the result.
+ *
+ * Returns:
+ *   %-ECHILD if the parent of @real is no longer the real dentry for @connected.
+ *   %-ESTALE if @real is not the real dentry of the found dentry.
+ *   Otherwise the found dentry is returned.
+ */
+static struct dentry *ovl_lookup_real_one(struct dentry *connected,
+					  struct dentry *real,
+					  const struct ovl_layer *layer)
+{
+	struct dentry *this;
+	struct name_snapshot name;
+	int err;
+
+	/*
+	 * We need to take a snapshot of real dentry name to protect us
+	 * from racing with underlying layer rename. In this case, we don't
+	 * care about returning ESTALE, only from dereferencing a free name
+	 * pointer because we hold no lock on the real dentry.
+	 */
+	take_dentry_name_snapshot(&name, real);
+	this = lookup_noperm_unlocked(&name.name, connected);
+	release_dentry_name_snapshot(&name);
+
+	err = -ECHILD;
+	if (ovl_dentry_real_at(connected, layer->idx) != real->d_parent)
+		goto fail;
+
+	err = PTR_ERR(this);
+	if (IS_ERR(this))
+		goto fail;
+
+	err = -ENOENT;
+	if (!this || !this->d_inode)
+		goto fail;
+
+	err = -ESTALE;
+	if (ovl_dentry_real_at(this, layer->idx) != real)
+		goto fail;
+
+	return this;
+
+fail:
+	pr_warn_ratelimited("failed to lookup one by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
+			    real, layer->idx, connected, err);
+	if (!IS_ERR(this))
+		dput(this);
+	return ERR_PTR(err);
+}
+
+static struct dentry *ovl_lookup_real(struct super_block *sb,
+				      struct dentry *real,
+				      const struct ovl_layer *layer);
+
+/*
+ * Lookup an indexed or hashed overlay dentry by real inode.
+ */
+static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
+					    struct dentry *real,
+					    const struct ovl_layer *layer)
+{
+	struct ovl_fs *ofs = OVL_FS(sb);
+	struct dentry *index = NULL;
+	struct dentry *this = NULL;
+	struct inode *inode;
+
+	/*
+	 * Decoding upper dir from index is expensive, so first try to lookup
+	 * overlay dentry in inode/dcache.
+	 */
+	inode = ovl_lookup_inode(sb, real, !layer->idx);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+	if (inode) {
+		this = d_find_any_alias(inode);
+		iput(inode);
+	}
+
+	/*
+	 * For decoded lower dir file handle, lookup index by origin to check
+	 * if lower dir was copied up and and/or removed.
+	 */
+	if (!this && layer->idx && ovl_indexdir(sb) && !WARN_ON(!d_is_dir(real))) {
+		index = ovl_lookup_index(ofs, NULL, real, false);
+		if (IS_ERR(index))
+			return index;
+	}
+
+	/* Get connected upper overlay dir from index */
+	if (index) {
+		struct dentry *upper = ovl_index_upper(ofs, index, true);
+
+		dput(index);
+		if (IS_ERR_OR_NULL(upper))
+			return upper;
+
+		/*
+		 * ovl_lookup_real() in lower layer may call recursively once to
+		 * ovl_lookup_real() in upper layer. The first level call walks
+		 * back lower parents to the topmost indexed parent. The second
+		 * recursive call walks back from indexed upper to the topmost
+		 * connected/hashed upper parent (or up to root).
+		 */
+		this = ovl_lookup_real(sb, upper, &ofs->layers[0]);
+		dput(upper);
+	}
+
+	if (IS_ERR_OR_NULL(this))
+		return this;
+
+	if (ovl_dentry_real_at(this, layer->idx) != real) {
+		dput(this);
+		this = ERR_PTR(-EIO);
+	}
+
+	return this;
+}
+
+/*
+ * Lookup an indexed or hashed overlay dentry, whose real dentry is an
+ * ancestor of @real.
+ */
+static struct dentry *ovl_lookup_real_ancestor(struct super_block *sb,
+					       struct dentry *real,
+					       const struct ovl_layer *layer)
+{
+	struct dentry *next, *parent = NULL;
+	struct dentry *ancestor = ERR_PTR(-EIO);
+
+	if (real == layer->mnt->mnt_root)
+		return dget(sb->s_root);
+
+	/* Find the topmost indexed or hashed ancestor */
+	next = dget(real);
+	for (;;) {
+		parent = dget_parent(next);
+
+		/*
+		 * Lookup a matching overlay dentry in inode/dentry
+		 * cache or in index by real inode.
+		 */
+		ancestor = ovl_lookup_real_inode(sb, next, layer);
+		if (ancestor)
+			break;
+
+		if (parent == layer->mnt->mnt_root) {
+			ancestor = dget(sb->s_root);
+			break;
+		}
+
+		/*
+		 * If @real has been moved out of the layer root directory,
+		 * we will eventully hit the real fs root. This cannot happen
+		 * by legit overlay rename, so we return error in that case.
+		 */
+		if (parent == next) {
+			ancestor = ERR_PTR(-EXDEV);
+			break;
+		}
+
+		dput(next);
+		next = parent;
+	}
+
+	dput(parent);
+	dput(next);
+
+	return ancestor;
+}
+
+/*
+ * Lookup a connected overlay dentry whose real dentry is @real.
+ * If @real is on upper layer, we lookup a child overlay dentry with the same
+ * path the real dentry. Otherwise, we need to consult index for lookup.
+ */
+static struct dentry *ovl_lookup_real(struct super_block *sb,
+				      struct dentry *real,
+				      const struct ovl_layer *layer)
+{
+	struct dentry *connected;
+	int err = 0;
+
+	connected = ovl_lookup_real_ancestor(sb, real, layer);
+	if (IS_ERR(connected))
+		return connected;
+
+	while (!err) {
+		struct dentry *next, *this;
+		struct dentry *parent = NULL;
+		struct dentry *real_connected = ovl_dentry_real_at(connected,
+								   layer->idx);
+
+		if (real_connected == real)
+			break;
+
+		/* Find the topmost dentry not yet connected */
+		next = dget(real);
+		for (;;) {
+			parent = dget_parent(next);
+
+			if (parent == real_connected)
+				break;
+
+			/*
+			 * If real has been moved out of 'real_connected',
+			 * we will not find 'real_connected' and hit the layer
+			 * root. In that case, we need to restart connecting.
+			 * This game can go on forever in the worst case. We
+			 * may want to consider taking s_vfs_rename_mutex if
+			 * this happens more than once.
+			 */
+			if (parent == layer->mnt->mnt_root) {
+				dput(connected);
+				connected = dget(sb->s_root);
+				break;
+			}
+
+			/*
+			 * If real file has been moved out of the layer root
+			 * directory, we will eventully hit the real fs root.
+			 * This cannot happen by legit overlay rename, so we
+			 * return error in that case.
+			 */
+			if (parent == next) {
+				err = -EXDEV;
+				break;
+			}
+
+			dput(next);
+			next = parent;
+		}
+
+		if (!err) {
+			this = ovl_lookup_real_one(connected, next, layer);
+			if (IS_ERR(this))
+				err = PTR_ERR(this);
+
+			/*
+			 * Lookup of child in overlay can fail when racing with
+			 * overlay rename of child away from 'connected' parent.
+			 * In this case, we need to restart the lookup from the
+			 * top, because we cannot trust that 'real_connected' is
+			 * still an ancestor of 'real'. There is a good chance
+			 * that the renamed overlay ancestor is now in cache, so
+			 * ovl_lookup_real_ancestor() will find it and we can
+			 * continue to connect exactly from where lookup failed.
+			 */
+			if (err == -ECHILD) {
+				this = ovl_lookup_real_ancestor(sb, real,
+								layer);
+				err = PTR_ERR_OR_ZERO(this);
+			}
+			if (!err) {
+				dput(connected);
+				connected = this;
+			}
+		}
+
+		dput(parent);
+		dput(next);
+	}
+
+	if (err)
+		goto fail;
+
+	return connected;
+
+fail:
+	pr_warn_ratelimited("failed to lookup by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
+			    real, layer->idx, connected, err);
+	dput(connected);
+	return ERR_PTR(err);
+}
+
+/*
+ * Get an overlay dentry from upper/lower real dentries and index.
+ */
+static struct dentry *ovl_get_dentry(struct super_block *sb,
+				     struct dentry *upper,
+				     struct ovl_path *lowerpath,
+				     struct dentry *index)
+{
+	struct ovl_fs *ofs = OVL_FS(sb);
+	const struct ovl_layer *layer = upper ? &ofs->layers[0] : lowerpath->layer;
+	struct dentry *real = upper ?: (index ?: lowerpath->dentry);
+
+	/*
+	 * Obtain a disconnected overlay dentry from a non-dir real dentry
+	 * and index.
+	 */
+	if (!d_is_dir(real))
+		return ovl_obtain_alias(sb, upper, lowerpath, index);
+
+	/* Removed empty directory? */
+	if ((real->d_flags & DCACHE_DISCONNECTED) || d_unhashed(real))
+		return ERR_PTR(-ENOENT);
+
+	/*
+	 * If real dentry is connected and hashed, get a connected overlay
+	 * dentry whose real dentry is @real.
+	 */
+	return ovl_lookup_real(sb, real, layer);
+}
+
+static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
+					struct ovl_fh *fh)
+{
+	struct ovl_fs *ofs = OVL_FS(sb);
+	struct dentry *dentry;
+	struct dentry *upper;
+
+	if (!ovl_upper_mnt(ofs))
+		return ERR_PTR(-EACCES);
+
+	upper = ovl_decode_real_fh(ofs, fh, ovl_upper_mnt(ofs), true);
+	if (IS_ERR_OR_NULL(upper))
+		return upper;
+
+	dentry = ovl_get_dentry(sb, upper, NULL, NULL);
+	dput(upper);
+
+	return dentry;
+}
+
+static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
+					struct ovl_fh *fh)
+{
+	struct ovl_fs *ofs = OVL_FS(sb);
+	struct ovl_path origin = { };
+	struct ovl_path *stack = &origin;
+	struct dentry *dentry = NULL;
+	struct dentry *index = NULL;
+	struct inode *inode;
+	int err;
+
+	/* First lookup overlay inode in inode cache by origin fh */
+	err = ovl_check_origin_fh(ofs, fh, false, NULL, &stack);
+	if (err)
+		return ERR_PTR(err);
+
+	if (!d_is_dir(origin.dentry) ||
+	    !(origin.dentry->d_flags & DCACHE_DISCONNECTED)) {
+		inode = ovl_lookup_inode(sb, origin.dentry, false);
+		err = PTR_ERR(inode);
+		if (IS_ERR(inode))
+			goto out_err;
+		if (inode) {
+			dentry = d_find_any_alias(inode);
+			iput(inode);
+			if (dentry)
+				goto out;
+		}
+	}
+
+	/* Then lookup indexed upper/whiteout by origin fh */
+	if (ovl_indexdir(sb)) {
+		index = ovl_get_index_fh(ofs, fh);
+		err = PTR_ERR(index);
+		if (IS_ERR(index)) {
+			index = NULL;
+			goto out_err;
+		}
+	}
+
+	/* Then try to get a connected upper dir by index */
+	if (index && d_is_dir(index)) {
+		struct dentry *upper = ovl_index_upper(ofs, index, true);
+
+		err = PTR_ERR(upper);
+		if (IS_ERR_OR_NULL(upper))
+			goto out_err;
+
+		dentry = ovl_get_dentry(sb, upper, NULL, NULL);
+		dput(upper);
+		goto out;
+	}
+
+	/* Find origin.dentry again with ovl_acceptable() layer check */
+	if (d_is_dir(origin.dentry)) {
+		dput(origin.dentry);
+		origin.dentry = NULL;
+		err = ovl_check_origin_fh(ofs, fh, true, NULL, &stack);
+		if (err)
+			goto out_err;
+	}
+	if (index) {
+		err = ovl_verify_origin(ofs, index, origin.dentry, false);
+		if (err)
+			goto out_err;
+	}
+
+	/* Get a connected non-upper dir or disconnected non-dir */
+	dentry = ovl_get_dentry(sb, NULL, &origin, index);
+
+out:
+	dput(origin.dentry);
+	dput(index);
+	return dentry;
+
+out_err:
+	dentry = ERR_PTR(err);
+	goto out;
+}
+
+static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
+{
+	struct ovl_fh *fh;
+
+	/* If on-wire inner fid is aligned - nothing to do */
+	if (fh_type == OVL_FILEID_V1)
+		return (struct ovl_fh *)fid;
+
+	if (fh_type != OVL_FILEID_V0)
+		return ERR_PTR(-EINVAL);
+
+	if (buflen <= OVL_FH_WIRE_OFFSET)
+		return ERR_PTR(-EINVAL);
+
+	fh = kzalloc(buflen, GFP_KERNEL);
+	if (!fh)
+		return ERR_PTR(-ENOMEM);
+
+	/* Copy unaligned inner fh into aligned buffer */
+	memcpy(fh->buf, fid, buflen - OVL_FH_WIRE_OFFSET);
+	return fh;
+}
+
+static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
+				       int fh_len, int fh_type)
+{
+	struct dentry *dentry = NULL;
+	struct ovl_fh *fh = NULL;
+	int len = fh_len << 2;
+	unsigned int flags = 0;
+	int err;
+
+	fh = ovl_fid_to_fh(fid, len, fh_type);
+	err = PTR_ERR(fh);
+	if (IS_ERR(fh))
+		goto out_err;
+
+	err = ovl_check_fh_len(fh, len);
+	if (err)
+		goto out_err;
+
+	flags = fh->fb.flags;
+	dentry = (flags & OVL_FH_FLAG_PATH_UPPER) ?
+		 ovl_upper_fh_to_d(sb, fh) :
+		 ovl_lower_fh_to_d(sb, fh);
+	err = PTR_ERR(dentry);
+	if (IS_ERR(dentry) && err != -ESTALE)
+		goto out_err;
+
+out:
+	/* We may have needed to re-align OVL_FILEID_V0 */
+	if (!IS_ERR_OR_NULL(fh) && fh != (void *)fid)
+		kfree(fh);
+
+	return dentry;
+
+out_err:
+	pr_warn_ratelimited("failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n",
+			    fh_len, fh_type, flags, err);
+	dentry = ERR_PTR(err);
+	goto out;
+}
+
+static struct dentry *ovl_fh_to_parent(struct super_block *sb, struct fid *fid,
+				       int fh_len, int fh_type)
+{
+	pr_warn_ratelimited("connectable file handles not supported; use 'no_subtree_check' exportfs option.\n");
+	return ERR_PTR(-EACCES);
+}
+
+static int ovl_get_name(struct dentry *parent, char *name,
+			struct dentry *child)
+{
+	/*
+	 * ovl_fh_to_dentry() returns connected dir overlay dentries and
+	 * ovl_fh_to_parent() is not implemented, so we should not get here.
+	 */
+	WARN_ON_ONCE(1);
+	return -EIO;
+}
+
+static struct dentry *ovl_get_parent(struct dentry *dentry)
+{
+	/*
+	 * ovl_fh_to_dentry() returns connected dir overlay dentries, so we
+	 * should not get here.
+	 */
+	WARN_ON_ONCE(1);
+	return ERR_PTR(-EIO);
+}
+
+const struct export_operations ovl_export_operations = {
+	.encode_fh	= ovl_encode_fh,
+	.fh_to_dentry	= ovl_fh_to_dentry,
+	.fh_to_parent	= ovl_fh_to_parent,
+	.get_name	= ovl_get_name,
+	.get_parent	= ovl_get_parent,
+};
+
+/* encode_fh() encodes non-decodable file handles with nfs_export=off */
+const struct export_operations ovl_export_fid_operations = {
+	.encode_fh	= ovl_encode_fh,
+};