#include <linux/types.h>
#include <linux/slab.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)
{
        /* Most of the code is block-size independent but currently we
         * use only 8: */
        BUG_ON(blocksize != 8);
        return 8 - (length & 7);
}

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], KM_USER0);
                pad = *(ptr + offset);
                kunmap_atomic(ptr, KM_USER0);
                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;
}

static void
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. */

u32
gss_wrap_kerberos(struct gss_ctx *ctx, int offset,
                struct xdr_buf *buf, struct page **pages)
{
        struct krb5_ctx         *kctx = ctx->internal_ctx_id;
        char                    cksumdata[16];
        struct xdr_netobj       md5cksum = {.len = 0, .data = cksumdata};
        int                     blocksize = 0, plainlen;
        unsigned char           *ptr, *msg_start;
        s32                     now;
        int                     headlen;
        struct page             **tmp_pages;
        u32                     seq_send;

        dprintk("RPC:       gss_wrap_kerberos\n");

        now = get_seconds();

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

        headlen = g_token_size(&kctx->mech_used, 24 + plainlen) -
                                                (buf->len - offset);

        ptr = buf->head[0].iov_base + offset;
        /* shift data to make room for header. */
        /* XXX Would be cleverer to encrypt while copying. */
        /* XXX bounds checking, slack, etc. */
        memmove(ptr + headlen, ptr, buf->head[0].iov_len - offset);
        buf->head[0].iov_len += headlen;
        buf->len += headlen;
        BUG_ON((buf->len - offset - headlen) % blocksize);

        g_make_token_header(&kctx->mech_used,
                                GSS_KRB5_TOK_HDR_LEN + 8 + 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 + 24;

        *(__be16 *)(ptr + 2) = htons(SGN_ALG_DES_MAC_MD5);
        memset(ptr + 4, 0xff, 4);
        *(__be16 *)(ptr + 4) = htons(SEAL_ALG_DES);

        make_confounder(msg_start, blocksize);

        /* XXXJBF: UGH!: */
        tmp_pages = buf->pages;
        buf->pages = pages;
        if (make_checksum("md5", ptr, 8, buf,
                                offset + headlen - blocksize, &md5cksum))
                return GSS_S_FAILURE;
        buf->pages = tmp_pages;

        if (krb5_encrypt(kctx->seq, NULL, md5cksum.data,
                          md5cksum.data, md5cksum.len))
                return GSS_S_FAILURE;
        memcpy(ptr + GSS_KRB5_TOK_HDR_LEN, md5cksum.data + md5cksum.len - 8, 8);

        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->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 - blocksize,
                                                                        pages))
                return GSS_S_FAILURE;

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

u32
gss_unwrap_kerberos(struct gss_ctx *ctx, int offset, struct xdr_buf *buf)
{
        struct krb5_ctx         *kctx = ctx->internal_ctx_id;
        int                     signalg;
        int                     sealalg;
        char                    cksumdata[16];
        struct xdr_netobj       md5cksum = {.len = 0, .data = cksumdata};
        s32                     now;
        int                     direction;
        s32                     seqnum;
        unsigned char           *ptr;
        int                     bodysize;
        void                    *data_start, *orig_start;
        int                     data_len;
        int                     blocksize;

        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 != SGN_ALG_DES_MAC_MD5)
                return GSS_S_DEFECTIVE_TOKEN;

        sealalg = ptr[4] + (ptr[5] << 8);
        if (sealalg != SEAL_ALG_DES)
                return GSS_S_DEFECTIVE_TOKEN;

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

        if (gss_decrypt_xdr_buf(kctx->enc, buf,
                        ptr + GSS_KRB5_TOK_HDR_LEN + 8 - (unsigned char *)buf->head[0].iov_base))
                return GSS_S_DEFECTIVE_TOKEN;

        if (make_checksum("md5", ptr, 8, buf,
                 ptr + GSS_KRB5_TOK_HDR_LEN + 8 - (unsigned char *)buf->head[0].iov_base, &md5cksum))
                return GSS_S_FAILURE;

        if (krb5_encrypt(kctx->seq, NULL, md5cksum.data,
                           md5cksum.data, md5cksum.len))
                return GSS_S_FAILURE;

        if (memcmp(md5cksum.data + 8, ptr + GSS_KRB5_TOK_HDR_LEN, 8))
                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 */

        if (krb5_get_seq_num(kctx->seq, 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_blkcipher_blocksize(kctx->enc);
        data_start = ptr + GSS_KRB5_TOK_HDR_LEN + 8 + blocksize;
        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;
}