linux/net/sunrpc/auth_gss/gss_krb5_crypto.c

/*
 *  linux/net/sunrpc/gss_krb5_crypto.c
 *
 *  Copyright (c) 2000-2008 The Regents of the University of Michigan.
 *  All rights reserved.
 *
 *  Andy Adamson   <[email protected]>
 *  Bruce Fields   <[email protected]>
 */

/*
 * Copyright (C) 1998 by the FundsXpress, INC.
 *
 * All rights reserved.
 *
 * Export of this software from the United States of America may require
 * a specific license from the United States Government.  It is the
 * responsibility of any person or organization contemplating export to
 * obtain such a license before exporting.
 *
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of FundsXpress. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  FundsXpress makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <crypto/hash.h>
#include <crypto/skcipher.h>
#include <crypto/utils.h>
#include <linux/err.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/scatterlist.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#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 …
#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)
{ … }

/**
 * 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_sync_skcipher *tfm,
	void * iv,
	void * in,
	void * out,
	int length)
{ … }

/**
 * krb5_decrypt - simple decryption of an RPCSEC GSS payload
 * @tfm: initialized cipher transform
 * @iv: pointer to an IV
 * @in: ciphertext to decrypt
 * @out: OUT: plaintext
 * @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 decrypted into @out
 *   negative errno: @in not decrypted
 */
u32
krb5_decrypt(
     struct crypto_sync_skcipher *tfm,
     void * iv,
     void * in,
     void * out,
     int length)
{ … }

static int
checksummer(struct scatterlist *sg, void *data)
{ … }

/*
 * 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
 */
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 - 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
gss_krb5_checksum(struct crypto_ahash *tfm, char *header, int hdrlen,
		  const struct xdr_buf *body, int body_offset,
		  struct xdr_netobj *cksumout)
{ … }
EXPORT_SYMBOL_IF_KUNIT(…);

struct encryptor_desc { … };

static int
encryptor(struct scatterlist *sg, void *data)
{ … }

int
gss_encrypt_xdr_buf(struct crypto_sync_skcipher *tfm, struct xdr_buf *buf,
		    int offset, struct page **pages)
{ … }

struct decryptor_desc { … };

static int
decryptor(struct scatterlist *sg, void *data)
{ … }

int
gss_decrypt_xdr_buf(struct crypto_sync_skcipher *tfm, struct xdr_buf *buf,
		    int offset)
{ … }

/*
 * This function makes the assumption that it was ultimately called
 * from gss_wrap().
 *
 * The client auth_gss code moves any existing tail data into a
 * separate page before calling gss_wrap.
 * The server svcauth_gss code ensures that both the head and the
 * tail have slack space of RPC_MAX_AUTH_SIZE before calling gss_wrap.
 *
 * Even with that guarantee, this function may be called more than
 * once in the processing of gss_wrap().  The best we can do is
 * verify at compile-time (see GSS_KRB5_SLACK_CHECK) that the
 * largest expected shift will fit within RPC_MAX_AUTH_SIZE.
 * At run-time we can verify that a single invocation of this
 * function doesn't attempt to use more the RPC_MAX_AUTH_SIZE.
 */

int
xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
{ … }

static u32
gss_krb5_cts_crypt(struct crypto_sync_skcipher *cipher, struct xdr_buf *buf,
		   u32 offset, u8 *iv, struct page **pages, int encrypt)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL_IF_KUNIT(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL_IF_KUNIT(…);

u32
gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
		     struct xdr_buf *buf, struct page **pages)
{ … }

u32
gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
		     struct xdr_buf *buf, u32 *headskip, u32 *tailskip)
{ … }

/**
 * 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
 */
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)
{ … }
EXPORT_SYMBOL_IF_KUNIT(…);

/**
 * 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)
{ … }

/**
 * krb5_etm_decrypt - Decrypt using the RFC 8009 rules
 * @kctx: Kerberos context
 * @offset: starting offset of the ciphertext, in bytes
 * @len:
 * @buf:
 * @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
 */
u32
krb5_etm_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
		 struct xdr_buf *buf, u32 *headskip, u32 *tailskip)
{ … }