Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 626 insertions, 0 deletions

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
new file mode 100644
index 0000000000..6eae3f12ad
--- /dev/null
+++ b/fs/crypto/fname.c
@@ -0,0 +1,626 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This contains functions for filename crypto management
+ *
+ * Copyright (C) 2015, Google, Inc.
+ * Copyright (C) 2015, Motorola Mobility
+ *
+ * Written by Uday Savagaonkar, 2014.
+ * Modified by Jaegeuk Kim, 2015.
+ *
+ * This has not yet undergone a rigorous security audit.
+ */
+
+#include <linux/namei.h>
+#include <linux/scatterlist.h>
+#include <crypto/hash.h>
+#include <crypto/sha2.h>
+#include <crypto/skcipher.h>
+#include "fscrypt_private.h"
+
+/*
+ * The minimum message length (input and output length), in bytes, for all
+ * filenames encryption modes.  Filenames shorter than this will be zero-padded
+ * before being encrypted.
+ */
+#define FSCRYPT_FNAME_MIN_MSG_LEN 16
+
+/*
+ * struct fscrypt_nokey_name - identifier for directory entry when key is absent
+ *
+ * When userspace lists an encrypted directory without access to the key, the
+ * filesystem must present a unique "no-key name" for each filename that allows
+ * it to find the directory entry again if requested.  Naively, that would just
+ * mean using the ciphertext filenames.  However, since the ciphertext filenames
+ * can contain illegal characters ('\0' and '/'), they must be encoded in some
+ * way.  We use base64url.  But that can cause names to exceed NAME_MAX (255
+ * bytes), so we also need to use a strong hash to abbreviate long names.
+ *
+ * The filesystem may also need another kind of hash, the "dirhash", to quickly
+ * find the directory entry.  Since filesystems normally compute the dirhash
+ * over the on-disk filename (i.e. the ciphertext), it's not computable from
+ * no-key names that abbreviate the ciphertext using the strong hash to fit in
+ * NAME_MAX.  It's also not computable if it's a keyed hash taken over the
+ * plaintext (but it may still be available in the on-disk directory entry);
+ * casefolded directories use this type of dirhash.  At least in these cases,
+ * each no-key name must include the name's dirhash too.
+ *
+ * To meet all these requirements, we base64url-encode the following
+ * variable-length structure.  It contains the dirhash, or 0's if the filesystem
+ * didn't provide one; up to 149 bytes of the ciphertext name; and for
+ * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
+ *
+ * This ensures that each no-key name contains everything needed to find the
+ * directory entry again, contains only legal characters, doesn't exceed
+ * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
+ * take the performance hit of SHA-256 on very long filenames (which are rare).
+ */
+struct fscrypt_nokey_name {
+	u32 dirhash[2];
+	u8 bytes[149];
+	u8 sha256[SHA256_DIGEST_SIZE];
+}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */
+
+/*
+ * Decoded size of max-size no-key name, i.e. a name that was abbreviated using
+ * the strong hash and thus includes the 'sha256' field.  This isn't simply
+ * sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.
+ */
+#define FSCRYPT_NOKEY_NAME_MAX	offsetofend(struct fscrypt_nokey_name, sha256)
+
+/* Encoded size of max-size no-key name */
+#define FSCRYPT_NOKEY_NAME_MAX_ENCODED \
+		FSCRYPT_BASE64URL_CHARS(FSCRYPT_NOKEY_NAME_MAX)
+
+static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
+{
+	if (str->len == 1 && str->name[0] == '.')
+		return true;
+
+	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
+		return true;
+
+	return false;
+}
+
+/**
+ * fscrypt_fname_encrypt() - encrypt a filename
+ * @inode: inode of the parent directory (for regular filenames)
+ *	   or of the symlink (for symlink targets). Key must already be
+ *	   set up.
+ * @iname: the filename to encrypt
+ * @out: (output) the encrypted filename
+ * @olen: size of the encrypted filename.  It must be at least @iname->len.
+ *	  Any extra space is filled with NUL padding before encryption.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
+			  u8 *out, unsigned int olen)
+{
+	struct skcipher_request *req = NULL;
+	DECLARE_CRYPTO_WAIT(wait);
+	const struct fscrypt_info *ci = inode->i_crypt_info;
+	struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
+	union fscrypt_iv iv;
+	struct scatterlist sg;
+	int res;
+
+	/*
+	 * Copy the filename to the output buffer for encrypting in-place and
+	 * pad it with the needed number of NUL bytes.
+	 */
+	if (WARN_ON_ONCE(olen < iname->len))
+		return -ENOBUFS;
+	memcpy(out, iname->name, iname->len);
+	memset(out + iname->len, 0, olen - iname->len);
+
+	/* Initialize the IV */
+	fscrypt_generate_iv(&iv, 0, ci);
+
+	/* Set up the encryption request */
+	req = skcipher_request_alloc(tfm, GFP_NOFS);
+	if (!req)
+		return -ENOMEM;
+	skcipher_request_set_callback(req,
+			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+			crypto_req_done, &wait);
+	sg_init_one(&sg, out, olen);
+	skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
+
+	/* Do the encryption */
+	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
+	skcipher_request_free(req);
+	if (res < 0) {
+		fscrypt_err(inode, "Filename encryption failed: %d", res);
+		return res;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt);
+
+/**
+ * fname_decrypt() - decrypt a filename
+ * @inode: inode of the parent directory (for regular filenames)
+ *	   or of the symlink (for symlink targets)
+ * @iname: the encrypted filename to decrypt
+ * @oname: (output) the decrypted filename.  The caller must have allocated
+ *	   enough space for this, e.g. using fscrypt_fname_alloc_buffer().
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int fname_decrypt(const struct inode *inode,
+			 const struct fscrypt_str *iname,
+			 struct fscrypt_str *oname)
+{
+	struct skcipher_request *req = NULL;
+	DECLARE_CRYPTO_WAIT(wait);
+	struct scatterlist src_sg, dst_sg;
+	const struct fscrypt_info *ci = inode->i_crypt_info;
+	struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
+	union fscrypt_iv iv;
+	int res;
+
+	/* Allocate request */
+	req = skcipher_request_alloc(tfm, GFP_NOFS);
+	if (!req)
+		return -ENOMEM;
+	skcipher_request_set_callback(req,
+		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+		crypto_req_done, &wait);
+
+	/* Initialize IV */
+	fscrypt_generate_iv(&iv, 0, ci);
+
+	/* Create decryption request */
+	sg_init_one(&src_sg, iname->name, iname->len);
+	sg_init_one(&dst_sg, oname->name, oname->len);
+	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
+	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
+	skcipher_request_free(req);
+	if (res < 0) {
+		fscrypt_err(inode, "Filename decryption failed: %d", res);
+		return res;
+	}
+
+	oname->len = strnlen(oname->name, iname->len);
+	return 0;
+}
+
+static const char base64url_table[65] =
+	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+#define FSCRYPT_BASE64URL_CHARS(nbytes)	DIV_ROUND_UP((nbytes) * 4, 3)
+
+/**
+ * fscrypt_base64url_encode() - base64url-encode some binary data
+ * @src: the binary data to encode
+ * @srclen: the length of @src in bytes
+ * @dst: (output) the base64url-encoded string.  Not NUL-terminated.
+ *
+ * Encodes data using base64url encoding, i.e. the "Base 64 Encoding with URL
+ * and Filename Safe Alphabet" specified by RFC 4648.  '='-padding isn't used,
+ * as it's unneeded and not required by the RFC.  base64url is used instead of
+ * base64 to avoid the '/' character, which isn't allowed in filenames.
+ *
+ * Return: the length of the resulting base64url-encoded string in bytes.
+ *	   This will be equal to FSCRYPT_BASE64URL_CHARS(srclen).
+ */
+static int fscrypt_base64url_encode(const u8 *src, int srclen, char *dst)
+{
+	u32 ac = 0;
+	int bits = 0;
+	int i;
+	char *cp = dst;
+
+	for (i = 0; i < srclen; i++) {
+		ac = (ac << 8) | src[i];
+		bits += 8;
+		do {
+			bits -= 6;
+			*cp++ = base64url_table[(ac >> bits) & 0x3f];
+		} while (bits >= 6);
+	}
+	if (bits)
+		*cp++ = base64url_table[(ac << (6 - bits)) & 0x3f];
+	return cp - dst;
+}
+
+/**
+ * fscrypt_base64url_decode() - base64url-decode a string
+ * @src: the string to decode.  Doesn't need to be NUL-terminated.
+ * @srclen: the length of @src in bytes
+ * @dst: (output) the decoded binary data
+ *
+ * Decodes a string using base64url encoding, i.e. the "Base 64 Encoding with
+ * URL and Filename Safe Alphabet" specified by RFC 4648.  '='-padding isn't
+ * accepted, nor are non-encoding characters such as whitespace.
+ *
+ * This implementation hasn't been optimized for performance.
+ *
+ * Return: the length of the resulting decoded binary data in bytes,
+ *	   or -1 if the string isn't a valid base64url string.
+ */
+static int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)
+{
+	u32 ac = 0;
+	int bits = 0;
+	int i;
+	u8 *bp = dst;
+
+	for (i = 0; i < srclen; i++) {
+		const char *p = strchr(base64url_table, src[i]);
+
+		if (p == NULL || src[i] == 0)
+			return -1;
+		ac = (ac << 6) | (p - base64url_table);
+		bits += 6;
+		if (bits >= 8) {
+			bits -= 8;
+			*bp++ = (u8)(ac >> bits);
+		}
+	}
+	if (ac & ((1 << bits) - 1))
+		return -1;
+	return bp - dst;
+}
+
+bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
+				    u32 orig_len, u32 max_len,
+				    u32 *encrypted_len_ret)
+{
+	int padding = 4 << (fscrypt_policy_flags(policy) &
+			    FSCRYPT_POLICY_FLAGS_PAD_MASK);
+	u32 encrypted_len;
+
+	if (orig_len > max_len)
+		return false;
+	encrypted_len = max_t(u32, orig_len, FSCRYPT_FNAME_MIN_MSG_LEN);
+	encrypted_len = round_up(encrypted_len, padding);
+	*encrypted_len_ret = min(encrypted_len, max_len);
+	return true;
+}
+
+/**
+ * fscrypt_fname_encrypted_size() - calculate length of encrypted filename
+ * @inode:		parent inode of dentry name being encrypted. Key must
+ *			already be set up.
+ * @orig_len:		length of the original filename
+ * @max_len:		maximum length to return
+ * @encrypted_len_ret:	where calculated length should be returned (on success)
+ *
+ * Filenames that are shorter than the maximum length may have their lengths
+ * increased slightly by encryption, due to padding that is applied.
+ *
+ * Return: false if the orig_len is greater than max_len. Otherwise, true and
+ *	   fill out encrypted_len_ret with the length (up to max_len).
+ */
+bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
+				  u32 max_len, u32 *encrypted_len_ret)
+{
+	return __fscrypt_fname_encrypted_size(&inode->i_crypt_info->ci_policy,
+					      orig_len, max_len,
+					      encrypted_len_ret);
+}
+EXPORT_SYMBOL_GPL(fscrypt_fname_encrypted_size);
+
+/**
+ * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
+ * @max_encrypted_len: maximum length of encrypted filenames the buffer will be
+ *		       used to present
+ * @crypto_str: (output) buffer to allocate
+ *
+ * Allocate a buffer that is large enough to hold any decrypted or encoded
+ * filename (null-terminated), for the given maximum encrypted filename length.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_fname_alloc_buffer(u32 max_encrypted_len,
+			       struct fscrypt_str *crypto_str)
+{
+	u32 max_presented_len = max_t(u32, FSCRYPT_NOKEY_NAME_MAX_ENCODED,
+				      max_encrypted_len);
+
+	crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
+	if (!crypto_str->name)
+		return -ENOMEM;
+	crypto_str->len = max_presented_len;
+	return 0;
+}
+EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
+
+/**
+ * fscrypt_fname_free_buffer() - free a buffer for presented filenames
+ * @crypto_str: the buffer to free
+ *
+ * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
+ */
+void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
+{
+	if (!crypto_str)
+		return;
+	kfree(crypto_str->name);
+	crypto_str->name = NULL;
+}
+EXPORT_SYMBOL(fscrypt_fname_free_buffer);
+
+/**
+ * fscrypt_fname_disk_to_usr() - convert an encrypted filename to
+ *				 user-presentable form
+ * @inode: inode of the parent directory (for regular filenames)
+ *	   or of the symlink (for symlink targets)
+ * @hash: first part of the name's dirhash, if applicable.  This only needs to
+ *	  be provided if the filename is located in an indexed directory whose
+ *	  encryption key may be unavailable.  Not needed for symlink targets.
+ * @minor_hash: second part of the name's dirhash, if applicable
+ * @iname: encrypted filename to convert.  May also be "." or "..", which
+ *	   aren't actually encrypted.
+ * @oname: output buffer for the user-presentable filename.  The caller must
+ *	   have allocated enough space for this, e.g. using
+ *	   fscrypt_fname_alloc_buffer().
+ *
+ * If the key is available, we'll decrypt the disk name.  Otherwise, we'll
+ * encode it for presentation in fscrypt_nokey_name format.
+ * See struct fscrypt_nokey_name for details.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_fname_disk_to_usr(const struct inode *inode,
+			      u32 hash, u32 minor_hash,
+			      const struct fscrypt_str *iname,
+			      struct fscrypt_str *oname)
+{
+	const struct qstr qname = FSTR_TO_QSTR(iname);
+	struct fscrypt_nokey_name nokey_name;
+	u32 size; /* size of the unencoded no-key name */
+
+	if (fscrypt_is_dot_dotdot(&qname)) {
+		oname->name[0] = '.';
+		oname->name[iname->len - 1] = '.';
+		oname->len = iname->len;
+		return 0;
+	}
+
+	if (iname->len < FSCRYPT_FNAME_MIN_MSG_LEN)
+		return -EUCLEAN;
+
+	if (fscrypt_has_encryption_key(inode))
+		return fname_decrypt(inode, iname, oname);
+
+	/*
+	 * Sanity check that struct fscrypt_nokey_name doesn't have padding
+	 * between fields and that its encoded size never exceeds NAME_MAX.
+	 */
+	BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
+		     offsetof(struct fscrypt_nokey_name, bytes));
+	BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
+		     offsetof(struct fscrypt_nokey_name, sha256));
+	BUILD_BUG_ON(FSCRYPT_NOKEY_NAME_MAX_ENCODED > NAME_MAX);
+
+	nokey_name.dirhash[0] = hash;
+	nokey_name.dirhash[1] = minor_hash;
+
+	if (iname->len <= sizeof(nokey_name.bytes)) {
+		memcpy(nokey_name.bytes, iname->name, iname->len);
+		size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
+	} else {
+		memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
+		/* Compute strong hash of remaining part of name. */
+		sha256(&iname->name[sizeof(nokey_name.bytes)],
+		       iname->len - sizeof(nokey_name.bytes),
+		       nokey_name.sha256);
+		size = FSCRYPT_NOKEY_NAME_MAX;
+	}
+	oname->len = fscrypt_base64url_encode((const u8 *)&nokey_name, size,
+					      oname->name);
+	return 0;
+}
+EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
+
+/**
+ * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
+ * @dir: the directory that will be searched
+ * @iname: the user-provided filename being searched for
+ * @lookup: 1 if we're allowed to proceed without the key because it's
+ *	->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
+ *	proceed without the key because we're going to create the dir_entry.
+ * @fname: the filename information to be filled in
+ *
+ * Given a user-provided filename @iname, this function sets @fname->disk_name
+ * to the name that would be stored in the on-disk directory entry, if possible.
+ * If the directory is unencrypted this is simply @iname.  Else, if we have the
+ * directory's encryption key, then @iname is the plaintext, so we encrypt it to
+ * get the disk_name.
+ *
+ * Else, for keyless @lookup operations, @iname should be a no-key name, so we
+ * decode it to get the struct fscrypt_nokey_name.  Non-@lookup operations will
+ * be impossible in this case, so we fail them with ENOKEY.
+ *
+ * If successful, fscrypt_free_filename() must be called later to clean up.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
+			      int lookup, struct fscrypt_name *fname)
+{
+	struct fscrypt_nokey_name *nokey_name;
+	int ret;
+
+	memset(fname, 0, sizeof(struct fscrypt_name));
+	fname->usr_fname = iname;
+
+	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
+		fname->disk_name.name = (unsigned char *)iname->name;
+		fname->disk_name.len = iname->len;
+		return 0;
+	}
+	ret = fscrypt_get_encryption_info(dir, lookup);
+	if (ret)
+		return ret;
+
+	if (fscrypt_has_encryption_key(dir)) {
+		if (!fscrypt_fname_encrypted_size(dir, iname->len, NAME_MAX,
+						  &fname->crypto_buf.len))
+			return -ENAMETOOLONG;
+		fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
+						 GFP_NOFS);
+		if (!fname->crypto_buf.name)
+			return -ENOMEM;
+
+		ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
+					    fname->crypto_buf.len);
+		if (ret)
+			goto errout;
+		fname->disk_name.name = fname->crypto_buf.name;
+		fname->disk_name.len = fname->crypto_buf.len;
+		return 0;
+	}
+	if (!lookup)
+		return -ENOKEY;
+	fname->is_nokey_name = true;
+
+	/*
+	 * We don't have the key and we are doing a lookup; decode the
+	 * user-supplied name
+	 */
+
+	if (iname->len > FSCRYPT_NOKEY_NAME_MAX_ENCODED)
+		return -ENOENT;
+
+	fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
+	if (fname->crypto_buf.name == NULL)
+		return -ENOMEM;
+
+	ret = fscrypt_base64url_decode(iname->name, iname->len,
+				       fname->crypto_buf.name);
+	if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||
+	    (ret > offsetof(struct fscrypt_nokey_name, sha256) &&
+	     ret != FSCRYPT_NOKEY_NAME_MAX)) {
+		ret = -ENOENT;
+		goto errout;
+	}
+	fname->crypto_buf.len = ret;
+
+	nokey_name = (void *)fname->crypto_buf.name;
+	fname->hash = nokey_name->dirhash[0];
+	fname->minor_hash = nokey_name->dirhash[1];
+	if (ret != FSCRYPT_NOKEY_NAME_MAX) {
+		/* The full ciphertext filename is available. */
+		fname->disk_name.name = nokey_name->bytes;
+		fname->disk_name.len =
+			ret - offsetof(struct fscrypt_nokey_name, bytes);
+	}
+	return 0;
+
+errout:
+	kfree(fname->crypto_buf.name);
+	return ret;
+}
+EXPORT_SYMBOL(fscrypt_setup_filename);
+
+/**
+ * fscrypt_match_name() - test whether the given name matches a directory entry
+ * @fname: the name being searched for
+ * @de_name: the name from the directory entry
+ * @de_name_len: the length of @de_name in bytes
+ *
+ * Normally @fname->disk_name will be set, and in that case we simply compare
+ * that to the name stored in the directory entry.  The only exception is that
+ * if we don't have the key for an encrypted directory and the name we're
+ * looking for is very long, then we won't have the full disk_name and instead
+ * we'll need to match against a fscrypt_nokey_name that includes a strong hash.
+ *
+ * Return: %true if the name matches, otherwise %false.
+ */
+bool fscrypt_match_name(const struct fscrypt_name *fname,
+			const u8 *de_name, u32 de_name_len)
+{
+	const struct fscrypt_nokey_name *nokey_name =
+		(const void *)fname->crypto_buf.name;
+	u8 digest[SHA256_DIGEST_SIZE];
+
+	if (likely(fname->disk_name.name)) {
+		if (de_name_len != fname->disk_name.len)
+			return false;
+		return !memcmp(de_name, fname->disk_name.name, de_name_len);
+	}
+	if (de_name_len <= sizeof(nokey_name->bytes))
+		return false;
+	if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
+		return false;
+	sha256(&de_name[sizeof(nokey_name->bytes)],
+	       de_name_len - sizeof(nokey_name->bytes), digest);
+	return !memcmp(digest, nokey_name->sha256, sizeof(digest));
+}
+EXPORT_SYMBOL_GPL(fscrypt_match_name);
+
+/**
+ * fscrypt_fname_siphash() - calculate the SipHash of a filename
+ * @dir: the parent directory
+ * @name: the filename to calculate the SipHash of
+ *
+ * Given a plaintext filename @name and a directory @dir which uses SipHash as
+ * its dirhash method and has had its fscrypt key set up, this function
+ * calculates the SipHash of that name using the directory's secret dirhash key.
+ *
+ * Return: the SipHash of @name using the hash key of @dir
+ */
+u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
+{
+	const struct fscrypt_info *ci = dir->i_crypt_info;
+
+	WARN_ON_ONCE(!ci->ci_dirhash_key_initialized);
+
+	return siphash(name->name, name->len, &ci->ci_dirhash_key);
+}
+EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
+
+/*
+ * Validate dentries in encrypted directories to make sure we aren't potentially
+ * caching stale dentries after a key has been added.
+ */
+int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
+{
+	struct dentry *dir;
+	int err;
+	int valid;
+
+	/*
+	 * Plaintext names are always valid, since fscrypt doesn't support
+	 * reverting to no-key names without evicting the directory's inode
+	 * -- which implies eviction of the dentries in the directory.
+	 */
+	if (!(dentry->d_flags & DCACHE_NOKEY_NAME))
+		return 1;
+
+	/*
+	 * No-key name; valid if the directory's key is still unavailable.
+	 *
+	 * Although fscrypt forbids rename() on no-key names, we still must use
+	 * dget_parent() here rather than use ->d_parent directly.  That's
+	 * because a corrupted fs image may contain directory hard links, which
+	 * the VFS handles by moving the directory's dentry tree in the dcache
+	 * each time ->lookup() finds the directory and it already has a dentry
+	 * elsewhere.  Thus ->d_parent can be changing, and we must safely grab
+	 * a reference to some ->d_parent to prevent it from being freed.
+	 */
+
+	if (flags & LOOKUP_RCU)
+		return -ECHILD;
+
+	dir = dget_parent(dentry);
+	/*
+	 * Pass allow_unsupported=true, so that files with an unsupported
+	 * encryption policy can be deleted.
+	 */
+	err = fscrypt_get_encryption_info(d_inode(dir), true);
+	valid = !fscrypt_has_encryption_key(d_inode(dir));
+	dput(dir);
+
+	if (err < 0)
+		return err;
+
+	return valid;
+}
+EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);