xref: /net/sunrpc/auth_gss/gss_krb5_wrap.c

/*
 * COPYRIGHT (c) 2008
 * The Regents of the University of Michigan
 * ALL RIGHTS RESERVED
 *
 * Permission is granted to use, copy, create derivative works
 * and redistribute this software and such derivative works
 * for any purpose, so long as the name of The University of
 * Michigan is not used in any advertising or publicity
 * pertaining to the use of distribution of this software
 * without specific, written prior authorization.  If the
 * above copyright notice or any other identification of the
 * University of Michigan is included in any copy of any
 * portion of this software, then the disclaimer below must
 * also be included.
 *
 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
 * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
 * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
 * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
 * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
 * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
 * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
 * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
 * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGES.
 */

#include <crypto/skcipher.h>
#include <linux/types.h>
#include <linux/jiffies.h>
#include <linux/sunrpc/gss_krb5.h>
#include <linux/random.h>
#include <linux/pagemap.h>

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY	RPCDBG_AUTH
#endif

static inline int
gss_krb5_padding(int blocksize, int length)
{
	return blocksize - (length % blocksize);
}

static inline void
gss_krb5_add_padding(struct xdr_buf *buf, int offset, int blocksize)
{
	int padding = gss_krb5_padding(blocksize, buf->len - offset);
	char *p;
	struct kvec *iov;

	if (buf->page_len || buf->tail[0].iov_len)
		iov = &buf->tail[0];
	else
		iov = &buf->head[0];
	p = iov->iov_base + iov->iov_len;
	iov->iov_len += padding;
	buf->len += padding;
	memset(p, padding, padding);
}

static inline int
gss_krb5_remove_padding(struct xdr_buf *buf, int blocksize)
{
	u8 *ptr;
	u8 pad;
	size_t len = buf->len;

	if (len <= buf->head[0].iov_len) {
		pad = *(u8 *)(buf->head[0].iov_base + len - 1);
		if (pad > buf->head[0].iov_len)
			return -EINVAL;
		buf->head[0].iov_len -= pad;
		goto out;
	} else
		len -= buf->head[0].iov_len;
	if (len <= buf->page_len) {
		unsigned int last = (buf->page_base + len - 1)
					>>PAGE_SHIFT;
		unsigned int offset = (buf->page_base + len - 1)
					& (PAGE_SIZE - 1);
		ptr = kmap_atomic(buf->pages[last]);
		pad = *(ptr + offset);
		kunmap_atomic(ptr);
		goto out;
	} else
		len -= buf->page_len;
	BUG_ON(len > buf->tail[0].iov_len);
	pad = *(u8 *)(buf->tail[0].iov_base + len - 1);
out:
	/* XXX: NOTE: we do not adjust the page lengths--they represent
	 * a range of data in the real filesystem page cache, and we need
	 * to know that range so the xdr code can properly place read data.
	 * However adjusting the head length, as we do above, is harmless.
	 * In the case of a request that fits into a single page, the server
	 * also uses length and head length together to determine the original
	 * start of the request to copy the request for deferal; so it's
	 * easier on the server if we adjust head and tail length in tandem.
	 * It's not really a problem that we don't fool with the page and
	 * tail lengths, though--at worst badly formed xdr might lead the
	 * server to attempt to parse the padding.
	 * XXX: Document all these weird requirements for gss mechanism
	 * wrap/unwrap functions. */
	if (pad > blocksize)
		return -EINVAL;
	if (buf->len > pad)
		buf->len -= pad;
	else
		return -EINVAL;
	return 0;
}

void
gss_krb5_make_confounder(char *p, u32 conflen)
{
	static u64 i = 0;
	u64 *q = (u64 *)p;

	/* rfc1964 claims this should be "random".  But all that's really
	 * necessary is that it be unique.  And not even that is necessary in
	 * our case since our "gssapi" implementation exists only to support
	 * rpcsec_gss, so we know that the only buffers we will ever encrypt
	 * already begin with a unique sequence number.  Just to hedge my bets
	 * I'll make a half-hearted attempt at something unique, but ensuring
	 * uniqueness would mean worrying about atomicity and rollover, and I
	 * don't care enough. */

	/* initialize to random value */
	if (i == 0) {
		i = prandom_u32();
		i = (i << 32) | prandom_u32();
	}

	switch (conflen) {
	case 16:
		*q++ = i++;
		fallthrough;
	case 8:
		*q++ = i++;
		break;
	default:
		BUG();
	}
}

/* Assumptions: the head and tail of inbuf are ours to play with.
 * The pages, however, may be real pages in the page cache and we replace
 * them with scratch pages from **pages before writing to them. */
/* XXX: obviously the above should be documentation of wrap interface,
 * and shouldn't be in this kerberos-specific file. */

/* XXX factor out common code with seal/unseal. */

static u32
gss_wrap_kerberos_v1(struct krb5_ctx *kctx, int offset,
		struct xdr_buf *buf, struct page **pages)
{
	char			cksumdata[GSS_KRB5_MAX_CKSUM_LEN];
	struct xdr_netobj	md5cksum = {.len = sizeof(cksumdata),
					    .data = cksumdata};
	int			blocksize = 0, plainlen;
	unsigned char		*ptr, *msg_start;
	time64_t		now;
	int			headlen;
	struct page		**tmp_pages;
	u32			seq_send;
	u8			*cksumkey;
	u32			conflen = kctx->gk5e->conflen;

	dprintk("RPC:       %s\n", __func__);

	now = ktime_get_real_seconds();

	blocksize = crypto_sync_skcipher_blocksize(kctx->enc);
	gss_krb5_add_padding(buf, offset, blocksize);
	BUG_ON((buf->len - offset) % blocksize);
	plainlen = conflen + buf->len - offset;

	headlen = g_token_size(&kctx->mech_used,
		GSS_KRB5_TOK_HDR_LEN + kctx->gk5e->cksumlength + plainlen) -
		(buf->len - offset);

	ptr = buf->head[0].iov_base + offset;
	/* shift data to make room for header. */
	xdr_extend_head(buf, offset, headlen);

	/* XXX Would be cleverer to encrypt while copying. */
	BUG_ON((buf->len - offset - headlen) % blocksize);

	g_make_token_header(&kctx->mech_used,
				GSS_KRB5_TOK_HDR_LEN +
				kctx->gk5e->cksumlength + plainlen, &ptr);


	/* ptr now at header described in rfc 1964, section 1.2.1: */
	ptr[0] = (unsigned char) ((KG_TOK_WRAP_MSG >> 8) & 0xff);
	ptr[1] = (unsigned char) (KG_TOK_WRAP_MSG & 0xff);

	msg_start = ptr + GSS_KRB5_TOK_HDR_LEN + kctx->gk5e->cksumlength;

	/*
	 * signalg and sealalg are stored as if they were converted from LE
	 * to host endian, even though they're opaque pairs of bytes according
	 * to the RFC.
	 */
	*(__le16 *)(ptr + 2) = cpu_to_le16(kctx->gk5e->signalg);
	*(__le16 *)(ptr + 4) = cpu_to_le16(kctx->gk5e->sealalg);
	ptr[6] = 0xff;
	ptr[7] = 0xff;

	gss_krb5_make_confounder(msg_start, conflen);

	if (kctx->gk5e->keyed_cksum)
		cksumkey = kctx->cksum;
	else
		cksumkey = NULL;

	/* XXXJBF: UGH!: */
	tmp_pages = buf->pages;
	buf->pages = pages;
	if (make_checksum(kctx, ptr, 8, buf, offset + headlen - conflen,
					cksumkey, KG_USAGE_SEAL, &md5cksum))
		return GSS_S_FAILURE;
	buf->pages = tmp_pages;

	memcpy(ptr + GSS_KRB5_TOK_HDR_LEN, md5cksum.data, md5cksum.len);

	seq_send = atomic_fetch_inc(&kctx->seq_send);

	/* XXX would probably be more efficient to compute checksum
	 * and encrypt at the same time: */
	if ((krb5_make_seq_num(kctx, kctx->seq, kctx->initiate ? 0 : 0xff,
			       seq_send, ptr + GSS_KRB5_TOK_HDR_LEN, ptr + 8)))
		return GSS_S_FAILURE;

	if (gss_encrypt_xdr_buf(kctx->enc, buf,
				offset + headlen - conflen, pages))
		return GSS_S_FAILURE;

	return (kctx->endtime < now) ? GSS_S_CONTEXT_EXPIRED : GSS_S_COMPLETE;
}

static u32
gss_unwrap_kerberos_v1(struct krb5_ctx *kctx, int offset, int len,
		       struct xdr_buf *buf, unsigned int *slack,
		       unsigned int *align)
{
	int			signalg;
	int			sealalg;
	char			cksumdata[GSS_KRB5_MAX_CKSUM_LEN];
	struct xdr_netobj	md5cksum = {.len = sizeof(cksumdata),
					    .data = cksumdata};
	time64_t		now;
	int			direction;
	s32			seqnum;
	unsigned char		*ptr;
	int			bodysize;
	void			*data_start, *orig_start;
	int			data_len;
	int			blocksize;
	u32			conflen = kctx->gk5e->conflen;
	int			crypt_offset;
	u8			*cksumkey;
	unsigned int		saved_len = buf->len;

	dprintk("RPC:       gss_unwrap_kerberos\n");

	ptr = (u8 *)buf->head[0].iov_base + offset;
	if (g_verify_token_header(&kctx->mech_used, &bodysize, &ptr,
					len - offset))
		return GSS_S_DEFECTIVE_TOKEN;

	if ((ptr[0] != ((KG_TOK_WRAP_MSG >> 8) & 0xff)) ||
	    (ptr[1] !=  (KG_TOK_WRAP_MSG & 0xff)))
		return GSS_S_DEFECTIVE_TOKEN;

	/* XXX sanity-check bodysize?? */

	/* get the sign and seal algorithms */

	signalg = ptr[2] + (ptr[3] << 8);
	if (signalg != kctx->gk5e->signalg)
		return GSS_S_DEFECTIVE_TOKEN;

	sealalg = ptr[4] + (ptr[5] << 8);
	if (sealalg != kctx->gk5e->sealalg)
		return GSS_S_DEFECTIVE_TOKEN;

	if ((ptr[6] != 0xff) || (ptr[7] != 0xff))
		return GSS_S_DEFECTIVE_TOKEN;

	/*
	 * Data starts after token header and checksum.  ptr points
	 * to the beginning of the token header
	 */
	crypt_offset = ptr + (GSS_KRB5_TOK_HDR_LEN + kctx->gk5e->cksumlength) -
					(unsigned char *)buf->head[0].iov_base;

	buf->len = len;
	if (gss_decrypt_xdr_buf(kctx->enc, buf, crypt_offset))
		return GSS_S_DEFECTIVE_TOKEN;

	if (kctx->gk5e->keyed_cksum)
		cksumkey = kctx->cksum;
	else
		cksumkey = NULL;

	if (make_checksum(kctx, ptr, 8, buf, crypt_offset,
					cksumkey, KG_USAGE_SEAL, &md5cksum))
		return GSS_S_FAILURE;

	if (memcmp(md5cksum.data, ptr + GSS_KRB5_TOK_HDR_LEN,
						kctx->gk5e->cksumlength))
		return GSS_S_BAD_SIG;

	/* it got through unscathed.  Make sure the context is unexpired */

	now = ktime_get_real_seconds();

	if (now > kctx->endtime)
		return GSS_S_CONTEXT_EXPIRED;

	/* do sequencing checks */

	if (krb5_get_seq_num(kctx, ptr + GSS_KRB5_TOK_HDR_LEN,
			     ptr + 8, &direction, &seqnum))
		return GSS_S_BAD_SIG;

	if ((kctx->initiate && direction != 0xff) ||
	    (!kctx->initiate && direction != 0))
		return GSS_S_BAD_SIG;

	/* Copy the data back to the right position.  XXX: Would probably be
	 * better to copy and encrypt at the same time. */

	blocksize = crypto_sync_skcipher_blocksize(kctx->enc);
	data_start = ptr + (GSS_KRB5_TOK_HDR_LEN + kctx->gk5e->cksumlength) +
					conflen;
	orig_start = buf->head[0].iov_base + offset;
	data_len = (buf->head[0].iov_base + buf->head[0].iov_len) - data_start;
	memmove(orig_start, data_start, data_len);
	buf->head[0].iov_len -= (data_start - orig_start);
	buf->len = len - (data_start - orig_start);

	if (gss_krb5_remove_padding(buf, blocksize))
		return GSS_S_DEFECTIVE_TOKEN;

	/* slack must include room for krb5 padding */
	*slack = XDR_QUADLEN(saved_len - buf->len);
	/* The GSS blob always precedes the RPC message payload */
	*align = *slack;
	return GSS_S_COMPLETE;
}

/*
 * We can shift data by up to LOCAL_BUF_LEN bytes in a pass.  If we need
 * to do more than that, we shift repeatedly.  Kevin Coffman reports
 * seeing 28 bytes as the value used by Microsoft clients and servers
 * with AES, so this constant is chosen to allow handling 28 in one pass
 * without using too much stack space.
 *
 * If that proves to a problem perhaps we could use a more clever
 * algorithm.
 */
#define LOCAL_BUF_LEN 32u

static void rotate_buf_a_little(struct xdr_buf *buf, unsigned int shift)
{
	char head[LOCAL_BUF_LEN];
	char tmp[LOCAL_BUF_LEN];
	unsigned int this_len, i;

	BUG_ON(shift > LOCAL_BUF_LEN);

	read_bytes_from_xdr_buf(buf, 0, head, shift);
	for (i = 0; i + shift < buf->len; i += LOCAL_BUF_LEN) {
		this_len = min(LOCAL_BUF_LEN, buf->len - (i + shift));
		read_bytes_from_xdr_buf(buf, i+shift, tmp, this_len);
		write_bytes_to_xdr_buf(buf, i, tmp, this_len);
	}
	write_bytes_to_xdr_buf(buf, buf->len - shift, head, shift);
}

static void _rotate_left(struct xdr_buf *buf, unsigned int shift)
{
	int shifted = 0;
	int this_shift;

	shift %= buf->len;
	while (shifted < shift) {
		this_shift = min(shift - shifted, LOCAL_BUF_LEN);
		rotate_buf_a_little(buf, this_shift);
		shifted += this_shift;
	}
}

static void rotate_left(u32 base, struct xdr_buf *buf, unsigned int shift)
{
	struct xdr_buf subbuf;

	xdr_buf_subsegment(buf, &subbuf, base, buf->len - base);
	_rotate_left(&subbuf, shift);
}

static u32
gss_wrap_kerberos_v2(struct krb5_ctx *kctx, u32 offset,
		     struct xdr_buf *buf, struct page **pages)
{
	u8		*ptr, *plainhdr;
	time64_t	now;
	u8		flags = 0x00;
	__be16		*be16ptr;
	__be64		*be64ptr;
	u32		err;

	dprintk("RPC:       %s\n", __func__);

	if (kctx->gk5e->encrypt_v2 == NULL)
		return GSS_S_FAILURE;

	/* make room for gss token header */
	if (xdr_extend_head(buf, offset, GSS_KRB5_TOK_HDR_LEN))
		return GSS_S_FAILURE;

	/* construct gss token header */
	ptr = plainhdr = buf->head[0].iov_base + offset;
	*ptr++ = (unsigned char) ((KG2_TOK_WRAP>>8) & 0xff);
	*ptr++ = (unsigned char) (KG2_TOK_WRAP & 0xff);

	if ((kctx->flags & KRB5_CTX_FLAG_INITIATOR) == 0)
		flags |= KG2_TOKEN_FLAG_SENTBYACCEPTOR;
	if ((kctx->flags & KRB5_CTX_FLAG_ACCEPTOR_SUBKEY) != 0)
		flags |= KG2_TOKEN_FLAG_ACCEPTORSUBKEY;
	/* We always do confidentiality in wrap tokens */
	flags |= KG2_TOKEN_FLAG_SEALED;

	*ptr++ = flags;
	*ptr++ = 0xff;
	be16ptr = (__be16 *)ptr;

	*be16ptr++ = 0;
	/* "inner" token header always uses 0 for RRC */
	*be16ptr++ = 0;

	be64ptr = (__be64 *)be16ptr;
	*be64ptr = cpu_to_be64(atomic64_fetch_inc(&kctx->seq_send64));

	err = (*kctx->gk5e->encrypt_v2)(kctx, offset, buf, pages);
	if (err)
		return err;

	now = ktime_get_real_seconds();
	return (kctx->endtime < now) ? GSS_S_CONTEXT_EXPIRED : GSS_S_COMPLETE;
}

static u32
gss_unwrap_kerberos_v2(struct krb5_ctx *kctx, int offset, int len,
		       struct xdr_buf *buf, unsigned int *slack,
		       unsigned int *align)
{
	time64_t	now;
	u8		*ptr;
	u8		flags = 0x00;
	u16		ec, rrc;
	int		err;
	u32		headskip, tailskip;
	u8		decrypted_hdr[GSS_KRB5_TOK_HDR_LEN];
	unsigned int	movelen;


	dprintk("RPC:       %s\n", __func__);

	if (kctx->gk5e->decrypt_v2 == NULL)
		return GSS_S_FAILURE;

	ptr = buf->head[0].iov_base + offset;

	if (be16_to_cpu(*((__be16 *)ptr)) != KG2_TOK_WRAP)
		return GSS_S_DEFECTIVE_TOKEN;

	flags = ptr[2];
	if ((!kctx->initiate && (flags & KG2_TOKEN_FLAG_SENTBYACCEPTOR)) ||
	    (kctx->initiate && !(flags & KG2_TOKEN_FLAG_SENTBYACCEPTOR)))
		return GSS_S_BAD_SIG;

	if ((flags & KG2_TOKEN_FLAG_SEALED) == 0) {
		dprintk("%s: token missing expected sealed flag\n", __func__);
		return GSS_S_DEFECTIVE_TOKEN;
	}

	if (ptr[3] != 0xff)
		return GSS_S_DEFECTIVE_TOKEN;

	ec = be16_to_cpup((__be16 *)(ptr + 4));
	rrc = be16_to_cpup((__be16 *)(ptr + 6));

	/*
	 * NOTE: the sequence number at ptr + 8 is skipped, rpcsec_gss
	 * doesn't want it checked; see page 6 of rfc 2203.
	 */

	if (rrc != 0)
		rotate_left(offset + 16, buf, rrc);

	err = (*kctx->gk5e->decrypt_v2)(kctx, offset, len, buf,
					&headskip, &tailskip);
	if (err)
		return GSS_S_FAILURE;

	/*
	 * Retrieve the decrypted gss token header and verify
	 * it against the original
	 */
	err = read_bytes_from_xdr_buf(buf,
				len - GSS_KRB5_TOK_HDR_LEN - tailskip,
				decrypted_hdr, GSS_KRB5_TOK_HDR_LEN);
	if (err) {
		dprintk("%s: error %u getting decrypted_hdr\n", __func__, err);
		return GSS_S_FAILURE;
	}
	if (memcmp(ptr, decrypted_hdr, 6)
				|| memcmp(ptr + 8, decrypted_hdr + 8, 8)) {
		dprintk("%s: token hdr, plaintext hdr mismatch!\n", __func__);
		return GSS_S_FAILURE;
	}

	/* do sequencing checks */

	/* it got through unscathed.  Make sure the context is unexpired */
	now = ktime_get_real_seconds();
	if (now > kctx->endtime)
		return GSS_S_CONTEXT_EXPIRED;

	/*
	 * Move the head data back to the right position in xdr_buf.
	 * We ignore any "ec" data since it might be in the head or
	 * the tail, and we really don't need to deal with it.
	 * Note that buf->head[0].iov_len may indicate the available
	 * head buffer space rather than that actually occupied.
	 */
	movelen = min_t(unsigned int, buf->head[0].iov_len, len);
	movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip;
	BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >
							buf->head[0].iov_len);
	memmove(ptr, ptr + GSS_KRB5_TOK_HDR_LEN + headskip, movelen);
	buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;
	buf->len = len - (GSS_KRB5_TOK_HDR_LEN + headskip);

	/* Trim off the trailing "extra count" and checksum blob */
	xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);

	*align = XDR_QUADLEN(GSS_KRB5_TOK_HDR_LEN + headskip);
	*slack = *align + XDR_QUADLEN(ec + GSS_KRB5_TOK_HDR_LEN + tailskip);
	return GSS_S_COMPLETE;
}

u32
gss_wrap_kerberos(struct gss_ctx *gctx, int offset,
		  struct xdr_buf *buf, struct page **pages)
{
	struct krb5_ctx	*kctx = gctx->internal_ctx_id;

	switch (kctx->enctype) {
	default:
		BUG();
	case ENCTYPE_DES_CBC_RAW:
	case ENCTYPE_DES3_CBC_RAW:
		return gss_wrap_kerberos_v1(kctx, offset, buf, pages);
	case ENCTYPE_AES128_CTS_HMAC_SHA1_96:
	case ENCTYPE_AES256_CTS_HMAC_SHA1_96:
		return gss_wrap_kerberos_v2(kctx, offset, buf, pages);
	}
}

u32
gss_unwrap_kerberos(struct gss_ctx *gctx, int offset,
		    int len, struct xdr_buf *buf)
{
	struct krb5_ctx	*kctx = gctx->internal_ctx_id;

	switch (kctx->enctype) {
	default:
		BUG();
	case ENCTYPE_DES_CBC_RAW:
	case ENCTYPE_DES3_CBC_RAW:
		return gss_unwrap_kerberos_v1(kctx, offset, len, buf,
					      &gctx->slack, &gctx->align);
	case ENCTYPE_AES128_CTS_HMAC_SHA1_96:
	case ENCTYPE_AES256_CTS_HMAC_SHA1_96:
		return gss_unwrap_kerberos_v2(kctx, offset, len, buf,
					      &gctx->slack, &gctx->align);
	}
}