1 files changed, 483 insertions, 611 deletions

diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index 12649c9fedab..16dcf115de1e 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -34,9 +34,9 @@
  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */
 
-#include <crypto/algapi.h>
 #include <crypto/hash.h>
 #include <crypto/skcipher.h>
+#include <crypto/utils.h>
 #include <linux/err.h>
 #include <linux/types.h>
 #include <linux/mm.h>
@@ -46,14 +46,62 @@
 #include <linux/random.h>
 #include <linux/sunrpc/gss_krb5.h>
 #include <linux/sunrpc/xdr.h>
+#include <kunit/visibility.h>
+
+#include "gss_krb5_internal.h"
 
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 # define RPCDBG_FACILITY        RPCDBG_AUTH
 #endif
 
+/**
+ * krb5_make_confounder - Generate a confounder string
+ * @p: memory location into which to write the string
+ * @conflen: string length to write, in octets
+ *
+ * RFCs 1964 and 3961 mention only "a random confounder" without going
+ * into detail about its function or cryptographic requirements. The
+ * assumed purpose is to prevent repeated encryption of a plaintext with
+ * the same key from generating the same ciphertext. It is also used to
+ * pad minimum plaintext length to at least a single cipher block.
+ *
+ * However, in situations like the GSS Kerberos 5 mechanism, where the
+ * encryption IV is always all zeroes, the confounder also effectively
+ * functions like an IV. Thus, not only must it be unique from message
+ * to message, but it must also be difficult to predict. Otherwise an
+ * attacker can correlate the confounder to previous or future values,
+ * making the encryption easier to break.
+ *
+ * Given that the primary consumer of this encryption mechanism is a
+ * network storage protocol, a type of traffic that often carries
+ * predictable payloads (eg, all zeroes when reading unallocated blocks
+ * from a file), our confounder generation has to be cryptographically
+ * strong.
+ */
+void krb5_make_confounder(u8 *p, int conflen)
+{
+	get_random_bytes(p, conflen);
+}
+
+/**
+ * krb5_encrypt - simple encryption of an RPCSEC GSS payload
+ * @tfm: initialized cipher transform
+ * @iv: pointer to an IV
+ * @in: plaintext to encrypt
+ * @out: OUT: ciphertext
+ * @length: length of input and output buffers, in bytes
+ *
+ * @iv may be NULL to force the use of an all-zero IV.
+ * The buffer containing the IV must be as large as the
+ * cipher's ivsize.
+ *
+ * Return values:
+ *   %0: @in successfully encrypted into @out
+ *   negative errno: @in not encrypted
+ */
 u32
 krb5_encrypt(
-	struct crypto_skcipher *tfm,
+	struct crypto_sync_skcipher *tfm,
 	void * iv,
 	void * in,
 	void * out,
@@ -62,24 +110,24 @@ krb5_encrypt(
 	u32 ret = -EINVAL;
 	struct scatterlist sg[1];
 	u8 local_iv[GSS_KRB5_MAX_BLOCKSIZE] = {0};
-	SKCIPHER_REQUEST_ON_STACK(req, tfm);
+	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);
 
-	if (length % crypto_skcipher_blocksize(tfm) != 0)
+	if (length % crypto_sync_skcipher_blocksize(tfm) != 0)
 		goto out;
 
-	if (crypto_skcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
+	if (crypto_sync_skcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
 		dprintk("RPC:       gss_k5encrypt: tfm iv size too large %d\n",
-			crypto_skcipher_ivsize(tfm));
+			crypto_sync_skcipher_ivsize(tfm));
 		goto out;
 	}
 
 	if (iv)
-		memcpy(local_iv, iv, crypto_skcipher_ivsize(tfm));
+		memcpy(local_iv, iv, crypto_sync_skcipher_ivsize(tfm));
 
 	memcpy(out, in, length);
 	sg_init_one(sg, out, length);
 
-	skcipher_request_set_tfm(req, tfm);
+	skcipher_request_set_sync_tfm(req, tfm);
 	skcipher_request_set_callback(req, 0, NULL, NULL);
 	skcipher_request_set_crypt(req, sg, sg, length, local_iv);
 
@@ -90,44 +138,6 @@ out:
 	return ret;
 }
 
-u32
-krb5_decrypt(
-     struct crypto_skcipher *tfm,
-     void * iv,
-     void * in,
-     void * out,
-     int length)
-{
-	u32 ret = -EINVAL;
-	struct scatterlist sg[1];
-	u8 local_iv[GSS_KRB5_MAX_BLOCKSIZE] = {0};
-	SKCIPHER_REQUEST_ON_STACK(req, tfm);
-
-	if (length % crypto_skcipher_blocksize(tfm) != 0)
-		goto out;
-
-	if (crypto_skcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
-		dprintk("RPC:       gss_k5decrypt: tfm iv size too large %d\n",
-			crypto_skcipher_ivsize(tfm));
-		goto out;
-	}
-	if (iv)
-		memcpy(local_iv,iv, crypto_skcipher_ivsize(tfm));
-
-	memcpy(out, in, length);
-	sg_init_one(sg, out, length);
-
-	skcipher_request_set_tfm(req, tfm);
-	skcipher_request_set_callback(req, 0, NULL, NULL);
-	skcipher_request_set_crypt(req, sg, sg, length, local_iv);
-
-	ret = crypto_skcipher_decrypt(req);
-	skcipher_request_zero(req);
-out:
-	dprintk("RPC:       gss_k5decrypt returns %d\n",ret);
-	return ret;
-}
-
 static int
 checksummer(struct scatterlist *sg, void *data)
 {
@@ -138,315 +148,78 @@ checksummer(struct scatterlist *sg, void *data)
 	return crypto_ahash_update(req);
 }
 
-static int
-arcfour_hmac_md5_usage_to_salt(unsigned int usage, u8 salt[4])
-{
-	unsigned int ms_usage;
-
-	switch (usage) {
-	case KG_USAGE_SIGN:
-		ms_usage = 15;
-		break;
-	case KG_USAGE_SEAL:
-		ms_usage = 13;
-		break;
-	default:
-		return -EINVAL;
-	}
-	salt[0] = (ms_usage >> 0) & 0xff;
-	salt[1] = (ms_usage >> 8) & 0xff;
-	salt[2] = (ms_usage >> 16) & 0xff;
-	salt[3] = (ms_usage >> 24) & 0xff;
-
-	return 0;
-}
-
-static u32
-make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
-		       struct xdr_buf *body, int body_offset, u8 *cksumkey,
-		       unsigned int usage, struct xdr_netobj *cksumout)
-{
-	struct scatterlist              sg[1];
-	int err = -1;
-	u8 *checksumdata;
-	u8 rc4salt[4];
-	struct crypto_ahash *md5;
-	struct crypto_ahash *hmac_md5;
-	struct ahash_request *req;
-
-	if (cksumkey == NULL)
-		return GSS_S_FAILURE;
-
-	if (cksumout->len < kctx->gk5e->cksumlength) {
-		dprintk("%s: checksum buffer length, %u, too small for %s\n",
-			__func__, cksumout->len, kctx->gk5e->name);
-		return GSS_S_FAILURE;
-	}
-
-	if (arcfour_hmac_md5_usage_to_salt(usage, rc4salt)) {
-		dprintk("%s: invalid usage value %u\n", __func__, usage);
-		return GSS_S_FAILURE;
-	}
-
-	checksumdata = kmalloc(GSS_KRB5_MAX_CKSUM_LEN, GFP_NOFS);
-	if (!checksumdata)
-		return GSS_S_FAILURE;
-
-	md5 = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC);
-	if (IS_ERR(md5))
-		goto out_free_cksum;
-
-	hmac_md5 = crypto_alloc_ahash(kctx->gk5e->cksum_name, 0,
-				      CRYPTO_ALG_ASYNC);
-	if (IS_ERR(hmac_md5))
-		goto out_free_md5;
-
-	req = ahash_request_alloc(md5, GFP_NOFS);
-	if (!req)
-		goto out_free_hmac_md5;
-
-	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
-
-	err = crypto_ahash_init(req);
-	if (err)
-		goto out;
-	sg_init_one(sg, rc4salt, 4);
-	ahash_request_set_crypt(req, sg, NULL, 4);
-	err = crypto_ahash_update(req);
-	if (err)
-		goto out;
-
-	sg_init_one(sg, header, hdrlen);
-	ahash_request_set_crypt(req, sg, NULL, hdrlen);
-	err = crypto_ahash_update(req);
-	if (err)
-		goto out;
-	err = xdr_process_buf(body, body_offset, body->len - body_offset,
-			      checksummer, req);
-	if (err)
-		goto out;
-	ahash_request_set_crypt(req, NULL, checksumdata, 0);
-	err = crypto_ahash_final(req);
-	if (err)
-		goto out;
-
-	ahash_request_free(req);
-	req = ahash_request_alloc(hmac_md5, GFP_NOFS);
-	if (!req)
-		goto out_free_hmac_md5;
-
-	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
-
-	err = crypto_ahash_init(req);
-	if (err)
-		goto out;
-	err = crypto_ahash_setkey(hmac_md5, cksumkey, kctx->gk5e->keylength);
-	if (err)
-		goto out;
-
-	sg_init_one(sg, checksumdata, crypto_ahash_digestsize(md5));
-	ahash_request_set_crypt(req, sg, checksumdata,
-				crypto_ahash_digestsize(md5));
-	err = crypto_ahash_digest(req);
-	if (err)
-		goto out;
-
-	memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
-	cksumout->len = kctx->gk5e->cksumlength;
-out:
-	ahash_request_free(req);
-out_free_hmac_md5:
-	crypto_free_ahash(hmac_md5);
-out_free_md5:
-	crypto_free_ahash(md5);
-out_free_cksum:
-	kfree(checksumdata);
-	return err ? GSS_S_FAILURE : 0;
-}
-
-/*
- * checksum the plaintext data and hdrlen bytes of the token header
- * The checksum is performed over the first 8 bytes of the
- * gss token header and then over the data body
+/**
+ * gss_krb5_checksum - Compute the MAC for a GSS Wrap or MIC token
+ * @tfm: an initialized hash transform
+ * @header: pointer to a buffer containing the token header, or NULL
+ * @hdrlen: number of octets in @header
+ * @body: xdr_buf containing an RPC message (body.len is the message length)
+ * @body_offset: byte offset into @body to start checksumming
+ * @cksumout: OUT: a buffer to be filled in with the computed HMAC
+ *
+ * Usually expressed as H = HMAC(K, message)[1..h] .
+ *
+ * Caller provides the truncation length of the output token (h) in
+ * cksumout.len.
+ *
+ * Return values:
+ *   %GSS_S_COMPLETE: Digest computed, @cksumout filled in
+ *   %GSS_S_FAILURE: Call failed
  */
 u32
-make_checksum(struct krb5_ctx *kctx, char *header, int hdrlen,
-	      struct xdr_buf *body, int body_offset, u8 *cksumkey,
-	      unsigned int usage, struct xdr_netobj *cksumout)
+gss_krb5_checksum(struct crypto_ahash *tfm, char *header, int hdrlen,
+		  const struct xdr_buf *body, int body_offset,
+		  struct xdr_netobj *cksumout)
 {
-	struct crypto_ahash *tfm;
 	struct ahash_request *req;
-	struct scatterlist              sg[1];
-	int err = -1;
+	int err = -ENOMEM;
 	u8 *checksumdata;
-	unsigned int checksumlen;
-
-	if (kctx->gk5e->ctype == CKSUMTYPE_HMAC_MD5_ARCFOUR)
-		return make_checksum_hmac_md5(kctx, header, hdrlen,
-					      body, body_offset,
-					      cksumkey, usage, cksumout);
-
-	if (cksumout->len < kctx->gk5e->cksumlength) {
-		dprintk("%s: checksum buffer length, %u, too small for %s\n",
-			__func__, cksumout->len, kctx->gk5e->name);
-		return GSS_S_FAILURE;
-	}
 
-	checksumdata = kmalloc(GSS_KRB5_MAX_CKSUM_LEN, GFP_NOFS);
-	if (checksumdata == NULL)
+	checksumdata = kmalloc(crypto_ahash_digestsize(tfm), GFP_KERNEL);
+	if (!checksumdata)
 		return GSS_S_FAILURE;
 
-	tfm = crypto_alloc_ahash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
-	if (IS_ERR(tfm))
-		goto out_free_cksum;
-
-	req = ahash_request_alloc(tfm, GFP_NOFS);
+	req = ahash_request_alloc(tfm, GFP_KERNEL);
 	if (!req)
-		goto out_free_ahash;
-
+		goto out_free_cksum;
 	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
-
-	checksumlen = crypto_ahash_digestsize(tfm);
-
-	if (cksumkey != NULL) {
-		err = crypto_ahash_setkey(tfm, cksumkey,
-					  kctx->gk5e->keylength);
-		if (err)
-			goto out;
-	}
-
 	err = crypto_ahash_init(req);
 	if (err)
-		goto out;
-	sg_init_one(sg, header, hdrlen);
-	ahash_request_set_crypt(req, sg, NULL, hdrlen);
-	err = crypto_ahash_update(req);
-	if (err)
-		goto out;
-	err = xdr_process_buf(body, body_offset, body->len - body_offset,
-			      checksummer, req);
-	if (err)
-		goto out;
-	ahash_request_set_crypt(req, NULL, checksumdata, 0);
-	err = crypto_ahash_final(req);
-	if (err)
-		goto out;
-
-	switch (kctx->gk5e->ctype) {
-	case CKSUMTYPE_RSA_MD5:
-		err = kctx->gk5e->encrypt(kctx->seq, NULL, checksumdata,
-					  checksumdata, checksumlen);
-		if (err)
-			goto out;
-		memcpy(cksumout->data,
-		       checksumdata + checksumlen - kctx->gk5e->cksumlength,
-		       kctx->gk5e->cksumlength);
-		break;
-	case CKSUMTYPE_HMAC_SHA1_DES3:
-		memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
-		break;
-	default:
-		BUG();
-		break;
-	}
-	cksumout->len = kctx->gk5e->cksumlength;
-out:
-	ahash_request_free(req);
-out_free_ahash:
-	crypto_free_ahash(tfm);
-out_free_cksum:
-	kfree(checksumdata);
-	return err ? GSS_S_FAILURE : 0;
-}
-
-/*
- * checksum the plaintext data and hdrlen bytes of the token header
- * Per rfc4121, sec. 4.2.4, the checksum is performed over the data
- * body then over the first 16 octets of the MIC token
- * Inclusion of the header data in the calculation of the
- * checksum is optional.
- */
-u32
-make_checksum_v2(struct krb5_ctx *kctx, char *header, int hdrlen,
-		 struct xdr_buf *body, int body_offset, u8 *cksumkey,
-		 unsigned int usage, struct xdr_netobj *cksumout)
-{
-	struct crypto_ahash *tfm;
-	struct ahash_request *req;
-	struct scatterlist sg[1];
-	int err = -1;
-	u8 *checksumdata;
-	unsigned int checksumlen;
-
-	if (kctx->gk5e->keyed_cksum == 0) {
-		dprintk("%s: expected keyed hash for %s\n",
-			__func__, kctx->gk5e->name);
-		return GSS_S_FAILURE;
-	}
-	if (cksumkey == NULL) {
-		dprintk("%s: no key supplied for %s\n",
-			__func__, kctx->gk5e->name);
-		return GSS_S_FAILURE;
-	}
-
-	checksumdata = kmalloc(GSS_KRB5_MAX_CKSUM_LEN, GFP_NOFS);
-	if (!checksumdata)
-		return GSS_S_FAILURE;
-
-	tfm = crypto_alloc_ahash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
-	if (IS_ERR(tfm))
-		goto out_free_cksum;
-	checksumlen = crypto_ahash_digestsize(tfm);
-
-	req = ahash_request_alloc(tfm, GFP_NOFS);
-	if (!req)
 		goto out_free_ahash;
 
-	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
-
-	err = crypto_ahash_setkey(tfm, cksumkey, kctx->gk5e->keylength);
-	if (err)
-		goto out;
-
-	err = crypto_ahash_init(req);
-	if (err)
-		goto out;
+	/*
+	 * Per RFC 4121 Section 4.2.4, the checksum is performed over the
+	 * data body first, then over the octets in "header".
+	 */
 	err = xdr_process_buf(body, body_offset, body->len - body_offset,
 			      checksummer, req);
 	if (err)
-		goto out;
-	if (header != NULL) {
+		goto out_free_ahash;
+	if (header) {
+		struct scatterlist sg[1];
+
 		sg_init_one(sg, header, hdrlen);
 		ahash_request_set_crypt(req, sg, NULL, hdrlen);
 		err = crypto_ahash_update(req);
 		if (err)
-			goto out;
+			goto out_free_ahash;
 	}
+
 	ahash_request_set_crypt(req, NULL, checksumdata, 0);
 	err = crypto_ahash_final(req);
 	if (err)
-		goto out;
+		goto out_free_ahash;
+
+	memcpy(cksumout->data, checksumdata,
+	       min_t(int, cksumout->len, crypto_ahash_digestsize(tfm)));
 
-	cksumout->len = kctx->gk5e->cksumlength;
-
-	switch (kctx->gk5e->ctype) {
-	case CKSUMTYPE_HMAC_SHA1_96_AES128:
-	case CKSUMTYPE_HMAC_SHA1_96_AES256:
-		/* note that this truncates the hash */
-		memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
-		break;
-	default:
-		BUG();
-		break;
-	}
-out:
-	ahash_request_free(req);
 out_free_ahash:
-	crypto_free_ahash(tfm);
+	ahash_request_free(req);
 out_free_cksum:
-	kfree(checksumdata);
-	return err ? GSS_S_FAILURE : 0;
+	kfree_sensitive(checksumdata);
+	return err ? GSS_S_FAILURE : GSS_S_COMPLETE;
 }
+EXPORT_SYMBOL_IF_KUNIT(gss_krb5_checksum);
 
 struct encryptor_desc {
 	u8 iv[GSS_KRB5_MAX_BLOCKSIZE];
@@ -465,7 +238,8 @@ encryptor(struct scatterlist *sg, void *data)
 {
 	struct encryptor_desc *desc = data;
 	struct xdr_buf *outbuf = desc->outbuf;
-	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(desc->req);
+	struct crypto_sync_skcipher *tfm =
+		crypto_sync_skcipher_reqtfm(desc->req);
 	struct page *in_page;
 	int thislen = desc->fraglen + sg->length;
 	int fraglen, ret;
@@ -491,7 +265,7 @@ encryptor(struct scatterlist *sg, void *data)
 	desc->fraglen += sg->length;
 	desc->pos += sg->length;
 
-	fraglen = thislen & (crypto_skcipher_blocksize(tfm) - 1);
+	fraglen = thislen & (crypto_sync_skcipher_blocksize(tfm) - 1);
 	thislen -= fraglen;
 
 	if (thislen == 0)
@@ -524,35 +298,6 @@ encryptor(struct scatterlist *sg, void *data)
 	return 0;
 }
 
-int
-gss_encrypt_xdr_buf(struct crypto_skcipher *tfm, struct xdr_buf *buf,
-		    int offset, struct page **pages)
-{
-	int ret;
-	struct encryptor_desc desc;
-	SKCIPHER_REQUEST_ON_STACK(req, tfm);
-
-	BUG_ON((buf->len - offset) % crypto_skcipher_blocksize(tfm) != 0);
-
-	skcipher_request_set_tfm(req, tfm);
-	skcipher_request_set_callback(req, 0, NULL, NULL);
-
-	memset(desc.iv, 0, sizeof(desc.iv));
-	desc.req = req;
-	desc.pos = offset;
-	desc.outbuf = buf;
-	desc.pages = pages;
-	desc.fragno = 0;
-	desc.fraglen = 0;
-
-	sg_init_table(desc.infrags, 4);
-	sg_init_table(desc.outfrags, 4);
-
-	ret = xdr_process_buf(buf, offset, buf->len - offset, encryptor, &desc);
-	skcipher_request_zero(req);
-	return ret;
-}
-
 struct decryptor_desc {
 	u8 iv[GSS_KRB5_MAX_BLOCKSIZE];
 	struct skcipher_request *req;
@@ -566,7 +311,8 @@ decryptor(struct scatterlist *sg, void *data)
 {
 	struct decryptor_desc *desc = data;
 	int thislen = desc->fraglen + sg->length;
-	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(desc->req);
+	struct crypto_sync_skcipher *tfm =
+		crypto_sync_skcipher_reqtfm(desc->req);
 	int fraglen, ret;
 
 	/* Worst case is 4 fragments: head, end of page 1, start
@@ -577,7 +323,7 @@ decryptor(struct scatterlist *sg, void *data)
 	desc->fragno++;
 	desc->fraglen += sg->length;
 
-	fraglen = thislen & (crypto_skcipher_blocksize(tfm) - 1);
+	fraglen = thislen & (crypto_sync_skcipher_blocksize(tfm) - 1);
 	thislen -= fraglen;
 
 	if (thislen == 0)
@@ -606,32 +352,6 @@ decryptor(struct scatterlist *sg, void *data)
 	return 0;
 }
 
-int
-gss_decrypt_xdr_buf(struct crypto_skcipher *tfm, struct xdr_buf *buf,
-		    int offset)
-{
-	int ret;
-	struct decryptor_desc desc;
-	SKCIPHER_REQUEST_ON_STACK(req, tfm);
-
-	/* XXXJBF: */
-	BUG_ON((buf->len - offset) % crypto_skcipher_blocksize(tfm) != 0);
-
-	skcipher_request_set_tfm(req, tfm);
-	skcipher_request_set_callback(req, 0, NULL, NULL);
-
-	memset(desc.iv, 0, sizeof(desc.iv));
-	desc.req = req;
-	desc.fragno = 0;
-	desc.fraglen = 0;
-
-	sg_init_table(desc.frags, 4);
-
-	ret = xdr_process_buf(buf, offset, buf->len - offset, decryptor, &desc);
-	skcipher_request_zero(req);
-	return ret;
-}
-
 /*
  * This function makes the assumption that it was ultimately called
  * from gss_wrap().
@@ -657,7 +377,6 @@ xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
 	if (shiftlen == 0)
 		return 0;
 
-	BUILD_BUG_ON(GSS_KRB5_MAX_SLACK_NEEDED > RPC_MAX_AUTH_SIZE);
 	BUG_ON(shiftlen > RPC_MAX_AUTH_SIZE);
 
 	p = buf->head[0].iov_base + base;
@@ -671,12 +390,12 @@ xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
 }
 
 static u32
-gss_krb5_cts_crypt(struct crypto_skcipher *cipher, struct xdr_buf *buf,
+gss_krb5_cts_crypt(struct crypto_sync_skcipher *cipher, struct xdr_buf *buf,
 		   u32 offset, u8 *iv, struct page **pages, int encrypt)
 {
 	u32 ret;
 	struct scatterlist sg[1];
-	SKCIPHER_REQUEST_ON_STACK(req, cipher);
+	SYNC_SKCIPHER_REQUEST_ON_STACK(req, cipher);
 	u8 *data;
 	struct page **save_pages;
 	u32 len = buf->len - offset;
@@ -685,7 +404,7 @@ gss_krb5_cts_crypt(struct crypto_skcipher *cipher, struct xdr_buf *buf,
 		WARN_ON(0);
 		return -ENOMEM;
 	}
-	data = kmalloc(GSS_KRB5_MAX_BLOCKSIZE * 2, GFP_NOFS);
+	data = kmalloc(GSS_KRB5_MAX_BLOCKSIZE * 2, GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
 
@@ -705,7 +424,7 @@ gss_krb5_cts_crypt(struct crypto_skcipher *cipher, struct xdr_buf *buf,
 
 	sg_init_one(sg, data, len);
 
-	skcipher_request_set_tfm(req, cipher);
+	skcipher_request_set_sync_tfm(req, cipher);
 	skcipher_request_set_callback(req, 0, NULL, NULL);
 	skcipher_request_set_crypt(req, sg, sg, len, iv);
 
@@ -721,45 +440,172 @@ gss_krb5_cts_crypt(struct crypto_skcipher *cipher, struct xdr_buf *buf,
 
 	ret = write_bytes_to_xdr_buf(buf, offset, data, len);
 
+#if IS_ENABLED(CONFIG_KUNIT)
+	/*
+	 * CBC-CTS does not define an output IV but RFC 3962 defines it as the
+	 * penultimate block of ciphertext, so copy that into the IV buffer
+	 * before returning.
+	 */
+	if (encrypt)
+		memcpy(iv, data, crypto_sync_skcipher_ivsize(cipher));
+#endif
+
 out:
 	kfree(data);
 	return ret;
 }
 
+/**
+ * krb5_cbc_cts_encrypt - encrypt in CBC mode with CTS
+ * @cts_tfm: CBC cipher with CTS
+ * @cbc_tfm: base CBC cipher
+ * @offset: starting byte offset for plaintext
+ * @buf: OUT: output buffer
+ * @pages: plaintext
+ * @iv: output CBC initialization vector, or NULL
+ * @ivsize: size of @iv, in octets
+ *
+ * To provide confidentiality, encrypt using cipher block chaining
+ * with ciphertext stealing. Message integrity is handled separately.
+ *
+ * Return values:
+ *   %0: encryption successful
+ *   negative errno: encryption could not be completed
+ */
+VISIBLE_IF_KUNIT
+int krb5_cbc_cts_encrypt(struct crypto_sync_skcipher *cts_tfm,
+			 struct crypto_sync_skcipher *cbc_tfm,
+			 u32 offset, struct xdr_buf *buf, struct page **pages,
+			 u8 *iv, unsigned int ivsize)
+{
+	u32 blocksize, nbytes, nblocks, cbcbytes;
+	struct encryptor_desc desc;
+	int err;
+
+	blocksize = crypto_sync_skcipher_blocksize(cts_tfm);
+	nbytes = buf->len - offset;
+	nblocks = (nbytes + blocksize - 1) / blocksize;
+	cbcbytes = 0;
+	if (nblocks > 2)
+		cbcbytes = (nblocks - 2) * blocksize;
+
+	memset(desc.iv, 0, sizeof(desc.iv));
+
+	/* Handle block-sized chunks of plaintext with CBC. */
+	if (cbcbytes) {
+		SYNC_SKCIPHER_REQUEST_ON_STACK(req, cbc_tfm);
+
+		desc.pos = offset;
+		desc.fragno = 0;
+		desc.fraglen = 0;
+		desc.pages = pages;
+		desc.outbuf = buf;
+		desc.req = req;
+
+		skcipher_request_set_sync_tfm(req, cbc_tfm);
+		skcipher_request_set_callback(req, 0, NULL, NULL);
+
+		sg_init_table(desc.infrags, 4);
+		sg_init_table(desc.outfrags, 4);
+
+		err = xdr_process_buf(buf, offset, cbcbytes, encryptor, &desc);
+		skcipher_request_zero(req);
+		if (err)
+			return err;
+	}
+
+	/* Remaining plaintext is handled with CBC-CTS. */
+	err = gss_krb5_cts_crypt(cts_tfm, buf, offset + cbcbytes,
+				 desc.iv, pages, 1);
+	if (err)
+		return err;
+
+	if (unlikely(iv))
+		memcpy(iv, desc.iv, ivsize);
+	return 0;
+}
+EXPORT_SYMBOL_IF_KUNIT(krb5_cbc_cts_encrypt);
+
+/**
+ * krb5_cbc_cts_decrypt - decrypt in CBC mode with CTS
+ * @cts_tfm: CBC cipher with CTS
+ * @cbc_tfm: base CBC cipher
+ * @offset: starting byte offset for plaintext
+ * @buf: OUT: output buffer
+ *
+ * Return values:
+ *   %0: decryption successful
+ *   negative errno: decryption could not be completed
+ */
+VISIBLE_IF_KUNIT
+int krb5_cbc_cts_decrypt(struct crypto_sync_skcipher *cts_tfm,
+			 struct crypto_sync_skcipher *cbc_tfm,
+			 u32 offset, struct xdr_buf *buf)
+{
+	u32 blocksize, nblocks, cbcbytes;
+	struct decryptor_desc desc;
+	int err;
+
+	blocksize = crypto_sync_skcipher_blocksize(cts_tfm);
+	nblocks = (buf->len + blocksize - 1) / blocksize;
+	cbcbytes = 0;
+	if (nblocks > 2)
+		cbcbytes = (nblocks - 2) * blocksize;
+
+	memset(desc.iv, 0, sizeof(desc.iv));
+
+	/* Handle block-sized chunks of plaintext with CBC. */
+	if (cbcbytes) {
+		SYNC_SKCIPHER_REQUEST_ON_STACK(req, cbc_tfm);
+
+		desc.fragno = 0;
+		desc.fraglen = 0;
+		desc.req = req;
+
+		skcipher_request_set_sync_tfm(req, cbc_tfm);
+		skcipher_request_set_callback(req, 0, NULL, NULL);
+
+		sg_init_table(desc.frags, 4);
+
+		err = xdr_process_buf(buf, 0, cbcbytes, decryptor, &desc);
+		skcipher_request_zero(req);
+		if (err)
+			return err;
+	}
+
+	/* Remaining plaintext is handled with CBC-CTS. */
+	return gss_krb5_cts_crypt(cts_tfm, buf, cbcbytes, desc.iv, NULL, 0);
+}
+EXPORT_SYMBOL_IF_KUNIT(krb5_cbc_cts_decrypt);
+
 u32
 gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
 		     struct xdr_buf *buf, struct page **pages)
 {
 	u32 err;
 	struct xdr_netobj hmac;
-	u8 *cksumkey;
 	u8 *ecptr;
-	struct crypto_skcipher *cipher, *aux_cipher;
-	int blocksize;
+	struct crypto_sync_skcipher *cipher, *aux_cipher;
+	struct crypto_ahash *ahash;
 	struct page **save_pages;
-	int nblocks, nbytes;
-	struct encryptor_desc desc;
-	u32 cbcbytes;
-	unsigned int usage;
+	unsigned int conflen;
 
 	if (kctx->initiate) {
 		cipher = kctx->initiator_enc;
 		aux_cipher = kctx->initiator_enc_aux;
-		cksumkey = kctx->initiator_integ;
-		usage = KG_USAGE_INITIATOR_SEAL;
+		ahash = kctx->initiator_integ;
 	} else {
 		cipher = kctx->acceptor_enc;
 		aux_cipher = kctx->acceptor_enc_aux;
-		cksumkey = kctx->acceptor_integ;
-		usage = KG_USAGE_ACCEPTOR_SEAL;
+		ahash = kctx->acceptor_integ;
 	}
-	blocksize = crypto_skcipher_blocksize(cipher);
+	conflen = crypto_sync_skcipher_blocksize(cipher);
 
 	/* hide the gss token header and insert the confounder */
 	offset += GSS_KRB5_TOK_HDR_LEN;
-	if (xdr_extend_head(buf, offset, kctx->gk5e->conflen))
+	if (xdr_extend_head(buf, offset, conflen))
 		return GSS_S_FAILURE;
-	gss_krb5_make_confounder(buf->head[0].iov_base + offset, kctx->gk5e->conflen);
+	krb5_make_confounder(buf->head[0].iov_base + offset, conflen);
 	offset -= GSS_KRB5_TOK_HDR_LEN;
 
 	if (buf->tail[0].iov_base != NULL) {
@@ -776,8 +622,7 @@ gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
 	buf->tail[0].iov_len += GSS_KRB5_TOK_HDR_LEN;
 	buf->len += GSS_KRB5_TOK_HDR_LEN;
 
-	/* Do the HMAC */
-	hmac.len = GSS_KRB5_MAX_CKSUM_LEN;
+	hmac.len = kctx->gk5e->cksumlength;
 	hmac.data = buf->tail[0].iov_base + buf->tail[0].iov_len;
 
 	/*
@@ -790,140 +635,64 @@ gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
 	save_pages = buf->pages;
 	buf->pages = pages;
 
-	err = make_checksum_v2(kctx, NULL, 0, buf,
-			       offset + GSS_KRB5_TOK_HDR_LEN,
-			       cksumkey, usage, &hmac);
+	err = gss_krb5_checksum(ahash, NULL, 0, buf,
+				offset + GSS_KRB5_TOK_HDR_LEN, &hmac);
 	buf->pages = save_pages;
 	if (err)
 		return GSS_S_FAILURE;
 
-	nbytes = buf->len - offset - GSS_KRB5_TOK_HDR_LEN;
-	nblocks = (nbytes + blocksize - 1) / blocksize;
-	cbcbytes = 0;
-	if (nblocks > 2)
-		cbcbytes = (nblocks - 2) * blocksize;
-
-	memset(desc.iv, 0, sizeof(desc.iv));
-
-	if (cbcbytes) {
-		SKCIPHER_REQUEST_ON_STACK(req, aux_cipher);
-
-		desc.pos = offset + GSS_KRB5_TOK_HDR_LEN;
-		desc.fragno = 0;
-		desc.fraglen = 0;
-		desc.pages = pages;
-		desc.outbuf = buf;
-		desc.req = req;
-
-		skcipher_request_set_tfm(req, aux_cipher);
-		skcipher_request_set_callback(req, 0, NULL, NULL);
-
-		sg_init_table(desc.infrags, 4);
-		sg_init_table(desc.outfrags, 4);
-
-		err = xdr_process_buf(buf, offset + GSS_KRB5_TOK_HDR_LEN,
-				      cbcbytes, encryptor, &desc);
-		skcipher_request_zero(req);
-		if (err)
-			goto out_err;
-	}
-
-	/* Make sure IV carries forward from any CBC results. */
-	err = gss_krb5_cts_crypt(cipher, buf,
-				 offset + GSS_KRB5_TOK_HDR_LEN + cbcbytes,
-				 desc.iv, pages, 1);
-	if (err) {
-		err = GSS_S_FAILURE;
-		goto out_err;
-	}
+	err = krb5_cbc_cts_encrypt(cipher, aux_cipher,
+				   offset + GSS_KRB5_TOK_HDR_LEN,
+				   buf, pages, NULL, 0);
+	if (err)
+		return GSS_S_FAILURE;
 
 	/* Now update buf to account for HMAC */
 	buf->tail[0].iov_len += kctx->gk5e->cksumlength;
 	buf->len += kctx->gk5e->cksumlength;
 
-out_err:
-	if (err)
-		err = GSS_S_FAILURE;
-	return err;
+	return GSS_S_COMPLETE;
 }
 
 u32
-gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, struct xdr_buf *buf,
-		     u32 *headskip, u32 *tailskip)
+gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
+		     struct xdr_buf *buf, u32 *headskip, u32 *tailskip)
 {
-	struct xdr_buf subbuf;
-	u32 ret = 0;
-	u8 *cksum_key;
-	struct crypto_skcipher *cipher, *aux_cipher;
+	struct crypto_sync_skcipher *cipher, *aux_cipher;
+	struct crypto_ahash *ahash;
 	struct xdr_netobj our_hmac_obj;
 	u8 our_hmac[GSS_KRB5_MAX_CKSUM_LEN];
 	u8 pkt_hmac[GSS_KRB5_MAX_CKSUM_LEN];
-	int nblocks, blocksize, cbcbytes;
-	struct decryptor_desc desc;
-	unsigned int usage;
+	struct xdr_buf subbuf;
+	u32 ret = 0;
 
 	if (kctx->initiate) {
 		cipher = kctx->acceptor_enc;
 		aux_cipher = kctx->acceptor_enc_aux;
-		cksum_key = kctx->acceptor_integ;
-		usage = KG_USAGE_ACCEPTOR_SEAL;
+		ahash = kctx->acceptor_integ;
 	} else {
 		cipher = kctx->initiator_enc;
 		aux_cipher = kctx->initiator_enc_aux;
-		cksum_key = kctx->initiator_integ;
-		usage = KG_USAGE_INITIATOR_SEAL;
+		ahash = kctx->initiator_integ;
 	}
-	blocksize = crypto_skcipher_blocksize(cipher);
-
 
 	/* create a segment skipping the header and leaving out the checksum */
 	xdr_buf_subsegment(buf, &subbuf, offset + GSS_KRB5_TOK_HDR_LEN,
-				    (buf->len - offset - GSS_KRB5_TOK_HDR_LEN -
+				    (len - offset - GSS_KRB5_TOK_HDR_LEN -
 				     kctx->gk5e->cksumlength));
 
-	nblocks = (subbuf.len + blocksize - 1) / blocksize;
-
-	cbcbytes = 0;
-	if (nblocks > 2)
-		cbcbytes = (nblocks - 2) * blocksize;
-
-	memset(desc.iv, 0, sizeof(desc.iv));
-
-	if (cbcbytes) {
-		SKCIPHER_REQUEST_ON_STACK(req, aux_cipher);
-
-		desc.fragno = 0;
-		desc.fraglen = 0;
-		desc.req = req;
-
-		skcipher_request_set_tfm(req, aux_cipher);
-		skcipher_request_set_callback(req, 0, NULL, NULL);
-
-		sg_init_table(desc.frags, 4);
-
-		ret = xdr_process_buf(&subbuf, 0, cbcbytes, decryptor, &desc);
-		skcipher_request_zero(req);
-		if (ret)
-			goto out_err;
-	}
-
-	/* Make sure IV carries forward from any CBC results. */
-	ret = gss_krb5_cts_crypt(cipher, &subbuf, cbcbytes, desc.iv, NULL, 0);
+	ret = krb5_cbc_cts_decrypt(cipher, aux_cipher, 0, &subbuf);
 	if (ret)
 		goto out_err;
 
-
-	/* Calculate our hmac over the plaintext data */
-	our_hmac_obj.len = sizeof(our_hmac);
+	our_hmac_obj.len = kctx->gk5e->cksumlength;
 	our_hmac_obj.data = our_hmac;
-
-	ret = make_checksum_v2(kctx, NULL, 0, &subbuf, 0,
-			       cksum_key, usage, &our_hmac_obj);
+	ret = gss_krb5_checksum(ahash, NULL, 0, &subbuf, 0, &our_hmac_obj);
 	if (ret)
 		goto out_err;
 
 	/* Get the packet's hmac value */
-	ret = read_bytes_from_xdr_buf(buf, buf->len - kctx->gk5e->cksumlength,
+	ret = read_bytes_from_xdr_buf(buf, len - kctx->gk5e->cksumlength,
 				      pkt_hmac, kctx->gk5e->cksumlength);
 	if (ret)
 		goto out_err;
@@ -932,7 +701,7 @@ gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, struct xdr_buf *buf,
 		ret = GSS_S_BAD_SIG;
 		goto out_err;
 	}
-	*headskip = kctx->gk5e->conflen;
+	*headskip = crypto_sync_skcipher_blocksize(cipher);
 	*tailskip = kctx->gk5e->cksumlength;
 out_err:
 	if (ret && ret != GSS_S_BAD_SIG)
@@ -940,144 +709,247 @@ out_err:
 	return ret;
 }
 
-/*
- * Compute Kseq given the initial session key and the checksum.
- * Set the key of the given cipher.
+/**
+ * krb5_etm_checksum - Compute a MAC for a GSS Wrap token
+ * @cipher: an initialized cipher transform
+ * @tfm: an initialized hash transform
+ * @body: xdr_buf containing an RPC message (body.len is the message length)
+ * @body_offset: byte offset into @body to start checksumming
+ * @cksumout: OUT: a buffer to be filled in with the computed HMAC
+ *
+ * Usually expressed as H = HMAC(K, IV | ciphertext)[1..h] .
+ *
+ * Caller provides the truncation length of the output token (h) in
+ * cksumout.len.
+ *
+ * Return values:
+ *   %GSS_S_COMPLETE: Digest computed, @cksumout filled in
+ *   %GSS_S_FAILURE: Call failed
  */
-int
-krb5_rc4_setup_seq_key(struct krb5_ctx *kctx, struct crypto_skcipher *cipher,
-		       unsigned char *cksum)
+VISIBLE_IF_KUNIT
+u32 krb5_etm_checksum(struct crypto_sync_skcipher *cipher,
+		      struct crypto_ahash *tfm, const struct xdr_buf *body,
+		      int body_offset, struct xdr_netobj *cksumout)
 {
-	struct crypto_shash *hmac;
-	struct shash_desc *desc;
-	u8 Kseq[GSS_KRB5_MAX_KEYLEN];
-	u32 zeroconstant = 0;
-	int err;
-
-	dprintk("%s: entered\n", __func__);
-
-	hmac = crypto_alloc_shash(kctx->gk5e->cksum_name, 0, 0);
-	if (IS_ERR(hmac)) {
-		dprintk("%s: error %ld, allocating hash '%s'\n",
-			__func__, PTR_ERR(hmac), kctx->gk5e->cksum_name);
-		return PTR_ERR(hmac);
-	}
-
-	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac),
-		       GFP_NOFS);
-	if (!desc) {
-		dprintk("%s: failed to allocate shash descriptor for '%s'\n",
-			__func__, kctx->gk5e->cksum_name);
-		crypto_free_shash(hmac);
-		return -ENOMEM;
-	}
+	unsigned int ivsize = crypto_sync_skcipher_ivsize(cipher);
+	struct ahash_request *req;
+	struct scatterlist sg[1];
+	u8 *iv, *checksumdata;
+	int err = -ENOMEM;
 
-	desc->tfm = hmac;
-	desc->flags = 0;
+	checksumdata = kmalloc(crypto_ahash_digestsize(tfm), GFP_KERNEL);
+	if (!checksumdata)
+		return GSS_S_FAILURE;
+	/* For RPCSEC, the "initial cipher state" is always all zeroes. */
+	iv = kzalloc(ivsize, GFP_KERNEL);
+	if (!iv)
+		goto out_free_mem;
 
-	/* Compute intermediate Kseq from session key */
-	err = crypto_shash_setkey(hmac, kctx->Ksess, kctx->gk5e->keylength);
+	req = ahash_request_alloc(tfm, GFP_KERNEL);
+	if (!req)
+		goto out_free_mem;
+	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
+	err = crypto_ahash_init(req);
 	if (err)
-		goto out_err;
+		goto out_free_ahash;
 
-	err = crypto_shash_digest(desc, (u8 *)&zeroconstant, 4, Kseq);
+	sg_init_one(sg, iv, ivsize);
+	ahash_request_set_crypt(req, sg, NULL, ivsize);
+	err = crypto_ahash_update(req);
 	if (err)
-		goto out_err;
+		goto out_free_ahash;
+	err = xdr_process_buf(body, body_offset, body->len - body_offset,
+			      checksummer, req);
+	if (err)
+		goto out_free_ahash;
 
-	/* Compute final Kseq from the checksum and intermediate Kseq */
-	err = crypto_shash_setkey(hmac, Kseq, kctx->gk5e->keylength);
+	ahash_request_set_crypt(req, NULL, checksumdata, 0);
+	err = crypto_ahash_final(req);
 	if (err)
-		goto out_err;
+		goto out_free_ahash;
+	memcpy(cksumout->data, checksumdata, cksumout->len);
+
+out_free_ahash:
+	ahash_request_free(req);
+out_free_mem:
+	kfree(iv);
+	kfree_sensitive(checksumdata);
+	return err ? GSS_S_FAILURE : GSS_S_COMPLETE;
+}
+EXPORT_SYMBOL_IF_KUNIT(krb5_etm_checksum);
+
+/**
+ * krb5_etm_encrypt - Encrypt using the RFC 8009 rules
+ * @kctx: Kerberos context
+ * @offset: starting offset of the payload, in bytes
+ * @buf: OUT: send buffer to contain the encrypted payload
+ * @pages: plaintext payload
+ *
+ * The main difference with aes_encrypt is that "The HMAC is
+ * calculated over the cipher state concatenated with the AES
+ * output, instead of being calculated over the confounder and
+ * plaintext.  This allows the message receiver to verify the
+ * integrity of the message before decrypting the message."
+ *
+ * RFC 8009 Section 5:
+ *
+ * encryption function: as follows, where E() is AES encryption in
+ * CBC-CS3 mode, and h is the size of truncated HMAC (128 bits or
+ * 192 bits as described above).
+ *
+ *    N = random value of length 128 bits (the AES block size)
+ *    IV = cipher state
+ *    C = E(Ke, N | plaintext, IV)
+ *    H = HMAC(Ki, IV | C)
+ *    ciphertext = C | H[1..h]
+ *
+ * This encryption formula provides AEAD EtM with key separation.
+ *
+ * Return values:
+ *   %GSS_S_COMPLETE: Encryption successful
+ *   %GSS_S_FAILURE: Encryption failed
+ */
+u32
+krb5_etm_encrypt(struct krb5_ctx *kctx, u32 offset,
+		 struct xdr_buf *buf, struct page **pages)
+{
+	struct crypto_sync_skcipher *cipher, *aux_cipher;
+	struct crypto_ahash *ahash;
+	struct xdr_netobj hmac;
+	unsigned int conflen;
+	u8 *ecptr;
+	u32 err;
 
-	err = crypto_shash_digest(desc, cksum, 8, Kseq);
+	if (kctx->initiate) {
+		cipher = kctx->initiator_enc;
+		aux_cipher = kctx->initiator_enc_aux;
+		ahash = kctx->initiator_integ;
+	} else {
+		cipher = kctx->acceptor_enc;
+		aux_cipher = kctx->acceptor_enc_aux;
+		ahash = kctx->acceptor_integ;
+	}
+	conflen = crypto_sync_skcipher_blocksize(cipher);
+
+	offset += GSS_KRB5_TOK_HDR_LEN;
+	if (xdr_extend_head(buf, offset, conflen))
+		return GSS_S_FAILURE;
+	krb5_make_confounder(buf->head[0].iov_base + offset, conflen);
+	offset -= GSS_KRB5_TOK_HDR_LEN;
+
+	if (buf->tail[0].iov_base) {
+		ecptr = buf->tail[0].iov_base + buf->tail[0].iov_len;
+	} else {
+		buf->tail[0].iov_base = buf->head[0].iov_base
+							+ buf->head[0].iov_len;
+		buf->tail[0].iov_len = 0;
+		ecptr = buf->tail[0].iov_base;
+	}
+
+	memcpy(ecptr, buf->head[0].iov_base + offset, GSS_KRB5_TOK_HDR_LEN);
+	buf->tail[0].iov_len += GSS_KRB5_TOK_HDR_LEN;
+	buf->len += GSS_KRB5_TOK_HDR_LEN;
+
+	err = krb5_cbc_cts_encrypt(cipher, aux_cipher,
+				   offset + GSS_KRB5_TOK_HDR_LEN,
+				   buf, pages, NULL, 0);
 	if (err)
-		goto out_err;
+		return GSS_S_FAILURE;
 
-	err = crypto_skcipher_setkey(cipher, Kseq, kctx->gk5e->keylength);
+	hmac.data = buf->tail[0].iov_base + buf->tail[0].iov_len;
+	hmac.len = kctx->gk5e->cksumlength;
+	err = krb5_etm_checksum(cipher, ahash,
+				buf, offset + GSS_KRB5_TOK_HDR_LEN, &hmac);
 	if (err)
 		goto out_err;
+	buf->tail[0].iov_len += kctx->gk5e->cksumlength;
+	buf->len += kctx->gk5e->cksumlength;
 
-	err = 0;
+	return GSS_S_COMPLETE;
 
 out_err:
-	kzfree(desc);
-	crypto_free_shash(hmac);
-	dprintk("%s: returning %d\n", __func__, err);
-	return err;
+	return GSS_S_FAILURE;
 }
 
-/*
- * Compute Kcrypt given the initial session key and the plaintext seqnum.
- * Set the key of cipher kctx->enc.
+/**
+ * krb5_etm_decrypt - Decrypt using the RFC 8009 rules
+ * @kctx: Kerberos context
+ * @offset: starting offset of the ciphertext, in bytes
+ * @len: size of ciphertext to unwrap
+ * @buf: ciphertext to unwrap
+ * @headskip: OUT: the enctype's confounder length, in octets
+ * @tailskip: OUT: the enctype's HMAC length, in octets
+ *
+ * RFC 8009 Section 5:
+ *
+ * decryption function: as follows, where D() is AES decryption in
+ * CBC-CS3 mode, and h is the size of truncated HMAC.
+ *
+ *    (C, H) = ciphertext
+ *        (Note: H is the last h bits of the ciphertext.)
+ *    IV = cipher state
+ *    if H != HMAC(Ki, IV | C)[1..h]
+ *        stop, report error
+ *    (N, P) = D(Ke, C, IV)
+ *
+ * Return values:
+ *   %GSS_S_COMPLETE: Decryption successful
+ *   %GSS_S_BAD_SIG: computed HMAC != received HMAC
+ *   %GSS_S_FAILURE: Decryption failed
  */
-int
-krb5_rc4_setup_enc_key(struct krb5_ctx *kctx, struct crypto_skcipher *cipher,
-		       s32 seqnum)
+u32
+krb5_etm_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
+		 struct xdr_buf *buf, u32 *headskip, u32 *tailskip)
 {
-	struct crypto_shash *hmac;
-	struct shash_desc *desc;
-	u8 Kcrypt[GSS_KRB5_MAX_KEYLEN];
-	u8 zeroconstant[4] = {0};
-	u8 seqnumarray[4];
-	int err, i;
-
-	dprintk("%s: entered, seqnum %u\n", __func__, seqnum);
-
-	hmac = crypto_alloc_shash(kctx->gk5e->cksum_name, 0, 0);
-	if (IS_ERR(hmac)) {
-		dprintk("%s: error %ld, allocating hash '%s'\n",
-			__func__, PTR_ERR(hmac), kctx->gk5e->cksum_name);
-		return PTR_ERR(hmac);
-	}
+	struct crypto_sync_skcipher *cipher, *aux_cipher;
+	u8 our_hmac[GSS_KRB5_MAX_CKSUM_LEN];
+	u8 pkt_hmac[GSS_KRB5_MAX_CKSUM_LEN];
+	struct xdr_netobj our_hmac_obj;
+	struct crypto_ahash *ahash;
+	struct xdr_buf subbuf;
+	u32 ret = 0;
 
-	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac),
-		       GFP_NOFS);
-	if (!desc) {
-		dprintk("%s: failed to allocate shash descriptor for '%s'\n",
-			__func__, kctx->gk5e->cksum_name);
-		crypto_free_shash(hmac);
-		return -ENOMEM;
+	if (kctx->initiate) {
+		cipher = kctx->acceptor_enc;
+		aux_cipher = kctx->acceptor_enc_aux;
+		ahash = kctx->acceptor_integ;
+	} else {
+		cipher = kctx->initiator_enc;
+		aux_cipher = kctx->initiator_enc_aux;
+		ahash = kctx->initiator_integ;
 	}
 
-	desc->tfm = hmac;
-	desc->flags = 0;
-
-	/* Compute intermediate Kcrypt from session key */
-	for (i = 0; i < kctx->gk5e->keylength; i++)
-		Kcrypt[i] = kctx->Ksess[i] ^ 0xf0;
-
-	err = crypto_shash_setkey(hmac, Kcrypt, kctx->gk5e->keylength);
-	if (err)
-		goto out_err;
+	/* Extract the ciphertext into @subbuf. */
+	xdr_buf_subsegment(buf, &subbuf, offset + GSS_KRB5_TOK_HDR_LEN,
+			   (len - offset - GSS_KRB5_TOK_HDR_LEN -
+			    kctx->gk5e->cksumlength));
 
-	err = crypto_shash_digest(desc, zeroconstant, 4, Kcrypt);
-	if (err)
+	our_hmac_obj.data = our_hmac;
+	our_hmac_obj.len = kctx->gk5e->cksumlength;
+	ret = krb5_etm_checksum(cipher, ahash, &subbuf, 0, &our_hmac_obj);
+	if (ret)
 		goto out_err;
-
-	/* Compute final Kcrypt from the seqnum and intermediate Kcrypt */
-	err = crypto_shash_setkey(hmac, Kcrypt, kctx->gk5e->keylength);
-	if (err)
+	ret = read_bytes_from_xdr_buf(buf, len - kctx->gk5e->cksumlength,
+				      pkt_hmac, kctx->gk5e->cksumlength);
+	if (ret)
 		goto out_err;
-
-	seqnumarray[0] = (unsigned char) ((seqnum >> 24) & 0xff);
-	seqnumarray[1] = (unsigned char) ((seqnum >> 16) & 0xff);
-	seqnumarray[2] = (unsigned char) ((seqnum >> 8) & 0xff);
-	seqnumarray[3] = (unsigned char) ((seqnum >> 0) & 0xff);
-
-	err = crypto_shash_digest(desc, seqnumarray, 4, Kcrypt);
-	if (err)
+	if (crypto_memneq(pkt_hmac, our_hmac, kctx->gk5e->cksumlength) != 0) {
+		ret = GSS_S_BAD_SIG;
 		goto out_err;
+	}
 
-	err = crypto_skcipher_setkey(cipher, Kcrypt, kctx->gk5e->keylength);
-	if (err)
+	ret = krb5_cbc_cts_decrypt(cipher, aux_cipher, 0, &subbuf);
+	if (ret) {
+		ret = GSS_S_FAILURE;
 		goto out_err;
+	}
 
-	err = 0;
+	*headskip = crypto_sync_skcipher_blocksize(cipher);
+	*tailskip = kctx->gk5e->cksumlength;
+	return GSS_S_COMPLETE;
 
 out_err:
-	kzfree(desc);
-	crypto_free_shash(hmac);
-	dprintk("%s: returning %d\n", __func__, err);
-	return err;
+	if (ret != GSS_S_BAD_SIG)
+		ret = GSS_S_FAILURE;
+	return ret;
 }
-