1 files changed, 719 insertions, 0 deletions

diff --git a/kernel/fs/ext4/crypto_fname.c b/kernel/fs/ext4/crypto_fname.c
new file mode 100644
index 000000000..fded02f72
--- /dev/null
+++ b/kernel/fs/ext4/crypto_fname.c
@@ -0,0 +1,719 @@
+/*
+ * linux/fs/ext4/crypto_fname.c
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains functions for filename crypto management in ext4
+ *
+ * Written by Uday Savagaonkar, 2014.
+ *
+ * This has not yet undergone a rigorous security audit.
+ *
+ */
+
+#include <crypto/hash.h>
+#include <crypto/sha.h>
+#include <keys/encrypted-type.h>
+#include <keys/user-type.h>
+#include <linux/crypto.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/key.h>
+#include <linux/key.h>
+#include <linux/list.h>
+#include <linux/mempool.h>
+#include <linux/random.h>
+#include <linux/scatterlist.h>
+#include <linux/spinlock_types.h>
+
+#include "ext4.h"
+#include "ext4_crypto.h"
+#include "xattr.h"
+
+/**
+ * ext4_dir_crypt_complete() -
+ */
+static void ext4_dir_crypt_complete(struct crypto_async_request *req, int res)
+{
+	struct ext4_completion_result *ecr = req->data;
+
+	if (res == -EINPROGRESS)
+		return;
+	ecr->res = res;
+	complete(&ecr->completion);
+}
+
+bool ext4_valid_filenames_enc_mode(uint32_t mode)
+{
+	return (mode == EXT4_ENCRYPTION_MODE_AES_256_CTS);
+}
+
+/**
+ * ext4_fname_encrypt() -
+ *
+ * This function encrypts the input filename, and returns the length of the
+ * ciphertext. Errors are returned as negative numbers.  We trust the caller to
+ * allocate sufficient memory to oname string.
+ */
+static int ext4_fname_encrypt(struct ext4_fname_crypto_ctx *ctx,
+			      const struct qstr *iname,
+			      struct ext4_str *oname)
+{
+	u32 ciphertext_len;
+	struct ablkcipher_request *req = NULL;
+	DECLARE_EXT4_COMPLETION_RESULT(ecr);
+	struct crypto_ablkcipher *tfm = ctx->ctfm;
+	int res = 0;
+	char iv[EXT4_CRYPTO_BLOCK_SIZE];
+	struct scatterlist sg[1];
+	int padding = 4 << (ctx->flags & EXT4_POLICY_FLAGS_PAD_MASK);
+	char *workbuf;
+
+	if (iname->len <= 0 || iname->len > ctx->lim)
+		return -EIO;
+
+	ciphertext_len = (iname->len < EXT4_CRYPTO_BLOCK_SIZE) ?
+		EXT4_CRYPTO_BLOCK_SIZE : iname->len;
+	ciphertext_len = ext4_fname_crypto_round_up(ciphertext_len, padding);
+	ciphertext_len = (ciphertext_len > ctx->lim)
+			? ctx->lim : ciphertext_len;
+
+	/* Allocate request */
+	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
+	if (!req) {
+		printk_ratelimited(
+		    KERN_ERR "%s: crypto_request_alloc() failed\n", __func__);
+		return -ENOMEM;
+	}
+	ablkcipher_request_set_callback(req,
+		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+		ext4_dir_crypt_complete, &ecr);
+
+	/* Map the workpage */
+	workbuf = kmap(ctx->workpage);
+
+	/* Copy the input */
+	memcpy(workbuf, iname->name, iname->len);
+	if (iname->len < ciphertext_len)
+		memset(workbuf + iname->len, 0, ciphertext_len - iname->len);
+
+	/* Initialize IV */
+	memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
+
+	/* Create encryption request */
+	sg_init_table(sg, 1);
+	sg_set_page(sg, ctx->workpage, PAGE_SIZE, 0);
+	ablkcipher_request_set_crypt(req, sg, sg, ciphertext_len, iv);
+	res = crypto_ablkcipher_encrypt(req);
+	if (res == -EINPROGRESS || res == -EBUSY) {
+		BUG_ON(req->base.data != &ecr);
+		wait_for_completion(&ecr.completion);
+		res = ecr.res;
+	}
+	if (res >= 0) {
+		/* Copy the result to output */
+		memcpy(oname->name, workbuf, ciphertext_len);
+		res = ciphertext_len;
+	}
+	kunmap(ctx->workpage);
+	ablkcipher_request_free(req);
+	if (res < 0) {
+		printk_ratelimited(
+		    KERN_ERR "%s: Error (error code %d)\n", __func__, res);
+	}
+	oname->len = ciphertext_len;
+	return res;
+}
+
+/*
+ * ext4_fname_decrypt()
+ *	This function decrypts the input filename, and returns
+ *	the length of the plaintext.
+ *	Errors are returned as negative numbers.
+ *	We trust the caller to allocate sufficient memory to oname string.
+ */
+static int ext4_fname_decrypt(struct ext4_fname_crypto_ctx *ctx,
+			      const struct ext4_str *iname,
+			      struct ext4_str *oname)
+{
+	struct ext4_str tmp_in[2], tmp_out[1];
+	struct ablkcipher_request *req = NULL;
+	DECLARE_EXT4_COMPLETION_RESULT(ecr);
+	struct scatterlist sg[1];
+	struct crypto_ablkcipher *tfm = ctx->ctfm;
+	int res = 0;
+	char iv[EXT4_CRYPTO_BLOCK_SIZE];
+	char *workbuf;
+
+	if (iname->len <= 0 || iname->len > ctx->lim)
+		return -EIO;
+
+	tmp_in[0].name = iname->name;
+	tmp_in[0].len = iname->len;
+	tmp_out[0].name = oname->name;
+
+	/* Allocate request */
+	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
+	if (!req) {
+		printk_ratelimited(
+		    KERN_ERR "%s: crypto_request_alloc() failed\n",  __func__);
+		return -ENOMEM;
+	}
+	ablkcipher_request_set_callback(req,
+		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+		ext4_dir_crypt_complete, &ecr);
+
+	/* Map the workpage */
+	workbuf = kmap(ctx->workpage);
+
+	/* Copy the input */
+	memcpy(workbuf, iname->name, iname->len);
+
+	/* Initialize IV */
+	memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
+
+	/* Create encryption request */
+	sg_init_table(sg, 1);
+	sg_set_page(sg, ctx->workpage, PAGE_SIZE, 0);
+	ablkcipher_request_set_crypt(req, sg, sg, iname->len, iv);
+	res = crypto_ablkcipher_decrypt(req);
+	if (res == -EINPROGRESS || res == -EBUSY) {
+		BUG_ON(req->base.data != &ecr);
+		wait_for_completion(&ecr.completion);
+		res = ecr.res;
+	}
+	if (res >= 0) {
+		/* Copy the result to output */
+		memcpy(oname->name, workbuf, iname->len);
+		res = iname->len;
+	}
+	kunmap(ctx->workpage);
+	ablkcipher_request_free(req);
+	if (res < 0) {
+		printk_ratelimited(
+		    KERN_ERR "%s: Error in ext4_fname_encrypt (error code %d)\n",
+		    __func__, res);
+		return res;
+	}
+
+	oname->len = strnlen(oname->name, iname->len);
+	return oname->len;
+}
+
+static const char *lookup_table =
+	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
+
+/**
+ * ext4_fname_encode_digest() -
+ *
+ * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
+ * The encoded string is roughly 4/3 times the size of the input string.
+ */
+static int digest_encode(const char *src, int len, char *dst)
+{
+	int i = 0, bits = 0, ac = 0;
+	char *cp = dst;
+
+	while (i < len) {
+		ac += (((unsigned char) src[i]) << bits);
+		bits += 8;
+		do {
+			*cp++ = lookup_table[ac & 0x3f];
+			ac >>= 6;
+			bits -= 6;
+		} while (bits >= 6);
+		i++;
+	}
+	if (bits)
+		*cp++ = lookup_table[ac & 0x3f];
+	return cp - dst;
+}
+
+static int digest_decode(const char *src, int len, char *dst)
+{
+	int i = 0, bits = 0, ac = 0;
+	const char *p;
+	char *cp = dst;
+
+	while (i < len) {
+		p = strchr(lookup_table, src[i]);
+		if (p == NULL || src[i] == 0)
+			return -2;
+		ac += (p - lookup_table) << bits;
+		bits += 6;
+		if (bits >= 8) {
+			*cp++ = ac & 0xff;
+			ac >>= 8;
+			bits -= 8;
+		}
+		i++;
+	}
+	if (ac)
+		return -1;
+	return cp - dst;
+}
+
+/**
+ * ext4_free_fname_crypto_ctx() -
+ *
+ * Frees up a crypto context.
+ */
+void ext4_free_fname_crypto_ctx(struct ext4_fname_crypto_ctx *ctx)
+{
+	if (ctx == NULL || IS_ERR(ctx))
+		return;
+
+	if (ctx->ctfm && !IS_ERR(ctx->ctfm))
+		crypto_free_ablkcipher(ctx->ctfm);
+	if (ctx->htfm && !IS_ERR(ctx->htfm))
+		crypto_free_hash(ctx->htfm);
+	if (ctx->workpage && !IS_ERR(ctx->workpage))
+		__free_page(ctx->workpage);
+	kfree(ctx);
+}
+
+/**
+ * ext4_put_fname_crypto_ctx() -
+ *
+ * Return: The crypto context onto free list. If the free list is above a
+ * threshold, completely frees up the context, and returns the memory.
+ *
+ * TODO: Currently we directly free the crypto context. Eventually we should
+ * add code it to return to free list. Such an approach will increase
+ * efficiency of directory lookup.
+ */
+void ext4_put_fname_crypto_ctx(struct ext4_fname_crypto_ctx **ctx)
+{
+	if (*ctx == NULL || IS_ERR(*ctx))
+		return;
+	ext4_free_fname_crypto_ctx(*ctx);
+	*ctx = NULL;
+}
+
+/**
+ * ext4_search_fname_crypto_ctx() -
+ */
+static struct ext4_fname_crypto_ctx *ext4_search_fname_crypto_ctx(
+		const struct ext4_encryption_key *key)
+{
+	return NULL;
+}
+
+/**
+ * ext4_alloc_fname_crypto_ctx() -
+ */
+struct ext4_fname_crypto_ctx *ext4_alloc_fname_crypto_ctx(
+	const struct ext4_encryption_key *key)
+{
+	struct ext4_fname_crypto_ctx *ctx;
+
+	ctx = kmalloc(sizeof(struct ext4_fname_crypto_ctx), GFP_NOFS);
+	if (ctx == NULL)
+		return ERR_PTR(-ENOMEM);
+	if (key->mode == EXT4_ENCRYPTION_MODE_INVALID) {
+		/* This will automatically set key mode to invalid
+		 * As enum for ENCRYPTION_MODE_INVALID is zero */
+		memset(&ctx->key, 0, sizeof(ctx->key));
+	} else {
+		memcpy(&ctx->key, key, sizeof(struct ext4_encryption_key));
+	}
+	ctx->has_valid_key = (EXT4_ENCRYPTION_MODE_INVALID == key->mode)
+		? 0 : 1;
+	ctx->ctfm_key_is_ready = 0;
+	ctx->ctfm = NULL;
+	ctx->htfm = NULL;
+	ctx->workpage = NULL;
+	return ctx;
+}
+
+/**
+ * ext4_get_fname_crypto_ctx() -
+ *
+ * Allocates a free crypto context and initializes it to hold
+ * the crypto material for the inode.
+ *
+ * Return: NULL if not encrypted. Error value on error. Valid pointer otherwise.
+ */
+struct ext4_fname_crypto_ctx *ext4_get_fname_crypto_ctx(
+	struct inode *inode, u32 max_ciphertext_len)
+{
+	struct ext4_fname_crypto_ctx *ctx;
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	int res;
+
+	/* Check if the crypto policy is set on the inode */
+	res = ext4_encrypted_inode(inode);
+	if (res == 0)
+		return NULL;
+
+	if (!ext4_has_encryption_key(inode))
+		ext4_generate_encryption_key(inode);
+
+	/* Get a crypto context based on the key.
+	 * A new context is allocated if no context matches the requested key.
+	 */
+	ctx = ext4_search_fname_crypto_ctx(&(ei->i_encryption_key));
+	if (ctx == NULL)
+		ctx = ext4_alloc_fname_crypto_ctx(&(ei->i_encryption_key));
+	if (IS_ERR(ctx))
+		return ctx;
+
+	ctx->flags = ei->i_crypt_policy_flags;
+	if (ctx->has_valid_key) {
+		if (ctx->key.mode != EXT4_ENCRYPTION_MODE_AES_256_CTS) {
+			printk_once(KERN_WARNING
+				    "ext4: unsupported key mode %d\n",
+				    ctx->key.mode);
+			return ERR_PTR(-ENOKEY);
+		}
+
+		/* As a first cut, we will allocate new tfm in every call.
+		 * later, we will keep the tfm around, in case the key gets
+		 * re-used */
+		if (ctx->ctfm == NULL) {
+			ctx->ctfm = crypto_alloc_ablkcipher("cts(cbc(aes))",
+					0, 0);
+		}
+		if (IS_ERR(ctx->ctfm)) {
+			res = PTR_ERR(ctx->ctfm);
+			printk(
+			    KERN_DEBUG "%s: error (%d) allocating crypto tfm\n",
+			    __func__, res);
+			ctx->ctfm = NULL;
+			ext4_put_fname_crypto_ctx(&ctx);
+			return ERR_PTR(res);
+		}
+		if (ctx->ctfm == NULL) {
+			printk(
+			    KERN_DEBUG "%s: could not allocate crypto tfm\n",
+			    __func__);
+			ext4_put_fname_crypto_ctx(&ctx);
+			return ERR_PTR(-ENOMEM);
+		}
+		if (ctx->workpage == NULL)
+			ctx->workpage = alloc_page(GFP_NOFS);
+		if (IS_ERR(ctx->workpage)) {
+			res = PTR_ERR(ctx->workpage);
+			printk(
+			    KERN_DEBUG "%s: error (%d) allocating work page\n",
+			    __func__, res);
+			ctx->workpage = NULL;
+			ext4_put_fname_crypto_ctx(&ctx);
+			return ERR_PTR(res);
+		}
+		if (ctx->workpage == NULL) {
+			printk(
+			    KERN_DEBUG "%s: could not allocate work page\n",
+			    __func__);
+			ext4_put_fname_crypto_ctx(&ctx);
+			return ERR_PTR(-ENOMEM);
+		}
+		ctx->lim = max_ciphertext_len;
+		crypto_ablkcipher_clear_flags(ctx->ctfm, ~0);
+		crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctx->ctfm),
+			CRYPTO_TFM_REQ_WEAK_KEY);
+
+		/* If we are lucky, we will get a context that is already
+		 * set up with the right key. Else, we will have to
+		 * set the key */
+		if (!ctx->ctfm_key_is_ready) {
+			/* Since our crypto objectives for filename encryption
+			 * are pretty weak,
+			 * we directly use the inode master key */
+			res = crypto_ablkcipher_setkey(ctx->ctfm,
+					ctx->key.raw, ctx->key.size);
+			if (res) {
+				ext4_put_fname_crypto_ctx(&ctx);
+				return ERR_PTR(-EIO);
+			}
+			ctx->ctfm_key_is_ready = 1;
+		} else {
+			/* In the current implementation, key should never be
+			 * marked "ready" for a context that has just been
+			 * allocated. So we should never reach here */
+			 BUG();
+		}
+	}
+	if (ctx->htfm == NULL)
+		ctx->htfm = crypto_alloc_hash("sha256", 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(ctx->htfm)) {
+		res = PTR_ERR(ctx->htfm);
+		printk(KERN_DEBUG "%s: error (%d) allocating hash tfm\n",
+			__func__, res);
+		ctx->htfm = NULL;
+		ext4_put_fname_crypto_ctx(&ctx);
+		return ERR_PTR(res);
+	}
+	if (ctx->htfm == NULL) {
+		printk(KERN_DEBUG "%s: could not allocate hash tfm\n",
+				__func__);
+		ext4_put_fname_crypto_ctx(&ctx);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	return ctx;
+}
+
+/**
+ * ext4_fname_crypto_round_up() -
+ *
+ * Return: The next multiple of block size
+ */
+u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
+{
+	return ((size+blksize-1)/blksize)*blksize;
+}
+
+/**
+ * ext4_fname_crypto_namelen_on_disk() -
+ */
+int ext4_fname_crypto_namelen_on_disk(struct ext4_fname_crypto_ctx *ctx,
+				      u32 namelen)
+{
+	u32 ciphertext_len;
+	int padding = 4 << (ctx->flags & EXT4_POLICY_FLAGS_PAD_MASK);
+
+	if (ctx == NULL)
+		return -EIO;
+	if (!(ctx->has_valid_key))
+		return -EACCES;
+	ciphertext_len = (namelen < EXT4_CRYPTO_BLOCK_SIZE) ?
+		EXT4_CRYPTO_BLOCK_SIZE : namelen;
+	ciphertext_len = ext4_fname_crypto_round_up(ciphertext_len, padding);
+	ciphertext_len = (ciphertext_len > ctx->lim)
+			? ctx->lim : ciphertext_len;
+	return (int) ciphertext_len;
+}
+
+/**
+ * ext4_fname_crypto_alloc_obuff() -
+ *
+ * Allocates an output buffer that is sufficient for the crypto operation
+ * specified by the context and the direction.
+ */
+int ext4_fname_crypto_alloc_buffer(struct ext4_fname_crypto_ctx *ctx,
+				   u32 ilen, struct ext4_str *crypto_str)
+{
+	unsigned int olen;
+	int padding = 4 << (ctx->flags & EXT4_POLICY_FLAGS_PAD_MASK);
+
+	if (!ctx)
+		return -EIO;
+	if (padding < EXT4_CRYPTO_BLOCK_SIZE)
+		padding = EXT4_CRYPTO_BLOCK_SIZE;
+	olen = ext4_fname_crypto_round_up(ilen, padding);
+	crypto_str->len = olen;
+	if (olen < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2)
+		olen = EXT4_FNAME_CRYPTO_DIGEST_SIZE*2;
+	/* Allocated buffer can hold one more character to null-terminate the
+	 * string */
+	crypto_str->name = kmalloc(olen+1, GFP_NOFS);
+	if (!(crypto_str->name))
+		return -ENOMEM;
+	return 0;
+}
+
+/**
+ * ext4_fname_crypto_free_buffer() -
+ *
+ * Frees the buffer allocated for crypto operation.
+ */
+void ext4_fname_crypto_free_buffer(struct ext4_str *crypto_str)
+{
+	if (!crypto_str)
+		return;
+	kfree(crypto_str->name);
+	crypto_str->name = NULL;
+}
+
+/**
+ * ext4_fname_disk_to_usr() - converts a filename from disk space to user space
+ */
+int _ext4_fname_disk_to_usr(struct ext4_fname_crypto_ctx *ctx,
+			    struct dx_hash_info *hinfo,
+			    const struct ext4_str *iname,
+			    struct ext4_str *oname)
+{
+	char buf[24];
+	int ret;
+
+	if (ctx == NULL)
+		return -EIO;
+	if (iname->len < 3) {
+		/*Check for . and .. */
+		if (iname->name[0] == '.' && iname->name[iname->len-1] == '.') {
+			oname->name[0] = '.';
+			oname->name[iname->len-1] = '.';
+			oname->len = iname->len;
+			return oname->len;
+		}
+	}
+	if (ctx->has_valid_key)
+		return ext4_fname_decrypt(ctx, iname, oname);
+
+	if (iname->len <= EXT4_FNAME_CRYPTO_DIGEST_SIZE) {
+		ret = digest_encode(iname->name, iname->len, oname->name);
+		oname->len = ret;
+		return ret;
+	}
+	if (hinfo) {
+		memcpy(buf, &hinfo->hash, 4);
+		memcpy(buf+4, &hinfo->minor_hash, 4);
+	} else
+		memset(buf, 0, 8);
+	memcpy(buf + 8, iname->name + iname->len - 16, 16);
+	oname->name[0] = '_';
+	ret = digest_encode(buf, 24, oname->name+1);
+	oname->len = ret + 1;
+	return ret + 1;
+}
+
+int ext4_fname_disk_to_usr(struct ext4_fname_crypto_ctx *ctx,
+			   struct dx_hash_info *hinfo,
+			   const struct ext4_dir_entry_2 *de,
+			   struct ext4_str *oname)
+{
+	struct ext4_str iname = {.name = (unsigned char *) de->name,
+				 .len = de->name_len };
+
+	return _ext4_fname_disk_to_usr(ctx, hinfo, &iname, oname);
+}
+
+
+/**
+ * ext4_fname_usr_to_disk() - converts a filename from user space to disk space
+ */
+int ext4_fname_usr_to_disk(struct ext4_fname_crypto_ctx *ctx,
+			   const struct qstr *iname,
+			   struct ext4_str *oname)
+{
+	int res;
+
+	if (ctx == NULL)
+		return -EIO;
+	if (iname->len < 3) {
+		/*Check for . and .. */
+		if (iname->name[0] == '.' &&
+				iname->name[iname->len-1] == '.') {
+			oname->name[0] = '.';
+			oname->name[iname->len-1] = '.';
+			oname->len = iname->len;
+			return oname->len;
+		}
+	}
+	if (ctx->has_valid_key) {
+		res = ext4_fname_encrypt(ctx, iname, oname);
+		return res;
+	}
+	/* Without a proper key, a user is not allowed to modify the filenames
+	 * in a directory. Consequently, a user space name cannot be mapped to
+	 * a disk-space name */
+	return -EACCES;
+}
+
+/*
+ * Calculate the htree hash from a filename from user space
+ */
+int ext4_fname_usr_to_hash(struct ext4_fname_crypto_ctx *ctx,
+			    const struct qstr *iname,
+			    struct dx_hash_info *hinfo)
+{
+	struct ext4_str tmp;
+	int ret = 0;
+	char buf[EXT4_FNAME_CRYPTO_DIGEST_SIZE+1];
+
+	if (!ctx ||
+	    ((iname->name[0] == '.') &&
+	     ((iname->len == 1) ||
+	      ((iname->name[1] == '.') && (iname->len == 2))))) {
+		ext4fs_dirhash(iname->name, iname->len, hinfo);
+		return 0;
+	}
+
+	if (!ctx->has_valid_key && iname->name[0] == '_') {
+		if (iname->len != 33)
+			return -ENOENT;
+		ret = digest_decode(iname->name+1, iname->len, buf);
+		if (ret != 24)
+			return -ENOENT;
+		memcpy(&hinfo->hash, buf, 4);
+		memcpy(&hinfo->minor_hash, buf + 4, 4);
+		return 0;
+	}
+
+	if (!ctx->has_valid_key && iname->name[0] != '_') {
+		if (iname->len > 43)
+			return -ENOENT;
+		ret = digest_decode(iname->name, iname->len, buf);
+		ext4fs_dirhash(buf, ret, hinfo);
+		return 0;
+	}
+
+	/* First encrypt the plaintext name */
+	ret = ext4_fname_crypto_alloc_buffer(ctx, iname->len, &tmp);
+	if (ret < 0)
+		return ret;
+
+	ret = ext4_fname_encrypt(ctx, iname, &tmp);
+	if (ret >= 0) {
+		ext4fs_dirhash(tmp.name, tmp.len, hinfo);
+		ret = 0;
+	}
+
+	ext4_fname_crypto_free_buffer(&tmp);
+	return ret;
+}
+
+int ext4_fname_match(struct ext4_fname_crypto_ctx *ctx, struct ext4_str *cstr,
+		     int len, const char * const name,
+		     struct ext4_dir_entry_2 *de)
+{
+	int ret = -ENOENT;
+	int bigname = (*name == '_');
+
+	if (ctx->has_valid_key) {
+		if (cstr->name == NULL) {
+			struct qstr istr;
+
+			ret = ext4_fname_crypto_alloc_buffer(ctx, len, cstr);
+			if (ret < 0)
+				goto errout;
+			istr.name = name;
+			istr.len = len;
+			ret = ext4_fname_encrypt(ctx, &istr, cstr);
+			if (ret < 0)
+				goto errout;
+		}
+	} else {
+		if (cstr->name == NULL) {
+			cstr->name = kmalloc(32, GFP_KERNEL);
+			if (cstr->name == NULL)
+				return -ENOMEM;
+			if ((bigname && (len != 33)) ||
+			    (!bigname && (len > 43)))
+				goto errout;
+			ret = digest_decode(name+bigname, len-bigname,
+					    cstr->name);
+			if (ret < 0) {
+				ret = -ENOENT;
+				goto errout;
+			}
+			cstr->len = ret;
+		}
+		if (bigname) {
+			if (de->name_len < 16)
+				return 0;
+			ret = memcmp(de->name + de->name_len - 16,
+				     cstr->name + 8, 16);
+			return (ret == 0) ? 1 : 0;
+		}
+	}
+	if (de->name_len != cstr->len)
+		return 0;
+	ret = memcmp(de->name, cstr->name, cstr->len);
+	return (ret == 0) ? 1 : 0;
+errout:
+	kfree(cstr->name);
+	cstr->name = NULL;
+	return ret;
+}