/*
 * 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 (kctx->enctype == ENCTYPE_ARCFOUR_HMAC) {
                struct crypto_sync_skcipher *cipher;
                int err;
                cipher = crypto_alloc_sync_skcipher(kctx->gk5e->encrypt_name,
                                                    0, 0);
                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_sync_skcipher(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, 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;

        /*
         * 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;

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

                cipher = crypto_alloc_sync_skcipher(kctx->gk5e->encrypt_name,
                                                    0, 0);
                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_sync_skcipher(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 = ktime_get_real_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_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:
        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,
                    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:
        case ENCTYPE_ARCFOUR_HMAC:
                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);
        }
}