/*
 * 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/pagemap.h>

#include "gss_krb5_internal.h"

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

/*
 * 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);
}

u32
gss_krb5_wrap_v2(struct krb5_ctx *kctx, int offset,
                 struct xdr_buf *buf, struct page **pages)
{
        u8              *ptr;
        time64_t        now;
        u8              flags = 0x00;
        __be16          *be16ptr;
        __be64          *be64ptr;
        u32             err;

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

        /* 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 = 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)(kctx, offset, buf, pages);
        if (err)
                return err;

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

u32
gss_krb5_unwrap_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__);

        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)(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;
}