gss_krb5_wrap.c

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

#ifdef RPC_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_CACHE_SHIFT;
        unsigned int offset = (buf->page_base + len - 1)
                    & (PAGE_CACHE_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 = random32();
        i = (i << 32) | random32();
    }

    switch (conflen) {
    case 16:
        *q++ = i++;
        /* fall through */
    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;
    s32         now;
    int         headlen;
    struct page     **tmp_pages;
    u32         seq_send;
    u8          *cksumkey;
    u32         conflen = kctx->gk5e->conflen;

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

    now = get_seconds();

    blocksize = crypto_blkcipher_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;

    *(__be16 *)(ptr + 2) = cpu_to_le16(kctx->gk5e->signalg);
    memset(ptr + 4, 0xff, 4);
    *(__be16 *)(ptr + 4) = cpu_to_le16(kctx->gk5e->sealalg);

    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);

    spin_lock(&krb5_seq_lock);
    seq_send = kctx->seq_send++;
    spin_unlock(&krb5_seq_lock);

    /* 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 (kctx->enctype == ENCTYPE_ARCFOUR_HMAC) {
        struct crypto_blkcipher *cipher;
        int err;
        cipher = crypto_alloc_blkcipher(kctx->gk5e->encrypt_name, 0,
                        CRYPTO_ALG_ASYNC);
        if (IS_ERR(cipher))
            return GSS_S_FAILURE;

        krb5_rc4_setup_enc_key(kctx, cipher, seq_send);

        err = gss_encrypt_xdr_buf(cipher, buf,
                      offset + headlen - conflen, pages);
        crypto_free_blkcipher(cipher);
        if (err)
            return GSS_S_FAILURE;
    } else {
        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, struct xdr_buf *buf)
{
    int         signalg;
    int         sealalg;
    char            cksumdata[GSS_KRB5_MAX_CKSUM_LEN];
    struct xdr_netobj   md5cksum = {.len = sizeof(cksumdata),
                        .data = cksumdata};
    s32         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;

    dprintk("RPC:       gss_unwrap_kerberos\n");

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

    /*
     * Need plaintext seqnum to derive encryption key for arcfour-hmac
     */
    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;

    if (kctx->enctype == ENCTYPE_ARCFOUR_HMAC) {
        struct crypto_blkcipher *cipher;
        int err;

        cipher = crypto_alloc_blkcipher(kctx->gk5e->encrypt_name, 0,
                        CRYPTO_ALG_ASYNC);
        if (IS_ERR(cipher))
            return GSS_S_FAILURE;

        krb5_rc4_setup_enc_key(kctx, cipher, seqnum);

        err = gss_decrypt_xdr_buf(cipher, buf, crypt_offset);
        crypto_free_blkcipher(cipher);
        if (err)
            return GSS_S_DEFECTIVE_TOKEN;
    } else {
        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 = get_seconds();

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

    /* do sequencing checks */

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

    blocksize = crypto_blkcipher_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 -= (data_start - orig_start);

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

    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)
{
    int     blocksize;
    u8      *ptr, *plainhdr;
    s32     now;
    u8      flags = 0x00;
    __be16      *be16ptr, ec = 0;
    __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;

    blocksize = crypto_blkcipher_blocksize(kctx->acceptor_enc);
    *be16ptr++ = cpu_to_be16(ec);
    /* "inner" token header always uses 0 for RRC */
    *be16ptr++ = cpu_to_be16(0);

    be64ptr = (__be64 *)be16ptr;
    spin_lock(&krb5_seq_lock);
    *be64ptr = cpu_to_be64(kctx->seq_send64++);
    spin_unlock(&krb5_seq_lock);

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

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

static u32
gss_unwrap_kerberos_v2(struct krb5_ctx *kctx, int offset, struct xdr_buf *buf)
{
    s32     now;
    u64     seqnum;
    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));

    seqnum = be64_to_cpup((__be64 *)(ptr + 8));

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

    err = (*kctx->gk5e->decrypt_v2)(kctx, offset, 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,
                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 = get_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, buf->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 -= GSS_KRB5_TOK_HDR_LEN + headskip;

    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:
    case ENCTYPE_ARCFOUR_HMAC:
        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, 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:
    case ENCTYPE_ARCFOUR_HMAC:
        return gss_unwrap_kerberos_v1(kctx, offset, buf);
    case ENCTYPE_AES128_CTS_HMAC_SHA1_96:
    case ENCTYPE_AES256_CTS_HMAC_SHA1_96:
        return gss_unwrap_kerberos_v2(kctx, offset, buf);
    }
}