/*
 * xfrm_replay.c - xfrm replay detection, derived from xfrm_state.c.
 *
 * Copyright (C) 2010 secunet Security Networks AG
 * Copyright (C) 2010 Steffen Klassert <steffen.klassert@secunet.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <linux/export.h>
#include <net/xfrm.h>

u32 xfrm_replay_seqhi(struct xfrm_state *x, __be32 net_seq)
{
        u32 seq, seq_hi, bottom;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;

        if (!(x->props.flags & XFRM_STATE_ESN))
                return 0;

        seq = ntohl(net_seq);
        seq_hi = replay_esn->seq_hi;
        bottom = replay_esn->seq - replay_esn->replay_window + 1;

        if (likely(replay_esn->seq >= replay_esn->replay_window - 1)) {
                /* A. same subspace */
                if (unlikely(seq < bottom))
                        seq_hi++;
        } else {
                /* B. window spans two subspaces */
                if (unlikely(seq >= bottom))
                        seq_hi--;
        }

        return seq_hi;
}

static void xfrm_replay_notify(struct xfrm_state *x, int event)
{
        struct km_event c;
        /* we send notify messages in case
         *  1. we updated on of the sequence numbers, and the seqno difference
         *     is at least x->replay_maxdiff, in this case we also update the
         *     timeout of our timer function
         *  2. if x->replay_maxage has elapsed since last update,
         *     and there were changes
         *
         *  The state structure must be locked!
         */

        switch (event) {
        case XFRM_REPLAY_UPDATE:
                if (!x->replay_maxdiff ||
                    ((x->replay.seq - x->preplay.seq < x->replay_maxdiff) &&
                    (x->replay.oseq - x->preplay.oseq < x->replay_maxdiff))) {
                        if (x->xflags & XFRM_TIME_DEFER)
                                event = XFRM_REPLAY_TIMEOUT;
                        else
                                return;
                }

                break;

        case XFRM_REPLAY_TIMEOUT:
                if (memcmp(&x->replay, &x->preplay,
                           sizeof(struct xfrm_replay_state)) == 0) {
                        x->xflags |= XFRM_TIME_DEFER;
                        return;
                }

                break;
        }

        memcpy(&x->preplay, &x->replay, sizeof(struct xfrm_replay_state));
        c.event = XFRM_MSG_NEWAE;
        c.data.aevent = event;
        km_state_notify(x, &c);

        if (x->replay_maxage &&
            !mod_timer(&x->rtimer, jiffies + x->replay_maxage))
                x->xflags &= ~XFRM_TIME_DEFER;
}

static int xfrm_replay_overflow(struct xfrm_state *x, struct sk_buff *skb)
{
        int err = 0;
        struct net *net = xs_net(x);

        if (x->type->flags & XFRM_TYPE_REPLAY_PROT) {
                XFRM_SKB_CB(skb)->seq.output.low = ++x->replay.oseq;
                if (unlikely(x->replay.oseq == 0)) {
                        x->replay.oseq--;
                        xfrm_audit_state_replay_overflow(x, skb);
                        err = -EOVERFLOW;

                        return err;
                }
                if (xfrm_aevent_is_on(net))
                        x->repl->notify(x, XFRM_REPLAY_UPDATE);
        }

        return err;
}

static int xfrm_replay_check(struct xfrm_state *x,
                      struct sk_buff *skb, __be32 net_seq)
{
        u32 diff;
        u32 seq = ntohl(net_seq);

        if (!x->props.replay_window)
                return 0;

        if (unlikely(seq == 0))
                goto err;

        if (likely(seq > x->replay.seq))
                return 0;

        diff = x->replay.seq - seq;
        if (diff >= x->props.replay_window) {
                x->stats.replay_window++;
                goto err;
        }

        if (x->replay.bitmap & (1U << diff)) {
                x->stats.replay++;
                goto err;
        }
        return 0;

err:
        xfrm_audit_state_replay(x, skb, net_seq);
        return -EINVAL;
}

static void xfrm_replay_advance(struct xfrm_state *x, __be32 net_seq)
{
        u32 diff;
        u32 seq = ntohl(net_seq);

        if (!x->props.replay_window)
                return;

        if (seq > x->replay.seq) {
                diff = seq - x->replay.seq;
                if (diff < x->props.replay_window)
                        x->replay.bitmap = ((x->replay.bitmap) << diff) | 1;
                else
                        x->replay.bitmap = 1;
                x->replay.seq = seq;
        } else {
                diff = x->replay.seq - seq;
                x->replay.bitmap |= (1U << diff);
        }

        if (xfrm_aevent_is_on(xs_net(x)))
                x->repl->notify(x, XFRM_REPLAY_UPDATE);
}

static int xfrm_replay_overflow_bmp(struct xfrm_state *x, struct sk_buff *skb)
{
        int err = 0;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        struct net *net = xs_net(x);

        if (x->type->flags & XFRM_TYPE_REPLAY_PROT) {
                XFRM_SKB_CB(skb)->seq.output.low = ++replay_esn->oseq;
                if (unlikely(replay_esn->oseq == 0)) {
                        replay_esn->oseq--;
                        xfrm_audit_state_replay_overflow(x, skb);
                        err = -EOVERFLOW;

                        return err;
                }
                if (xfrm_aevent_is_on(net))
                        x->repl->notify(x, XFRM_REPLAY_UPDATE);
        }

        return err;
}

static int xfrm_replay_check_bmp(struct xfrm_state *x,
                                 struct sk_buff *skb, __be32 net_seq)
{
        unsigned int bitnr, nr;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        u32 pos;
        u32 seq = ntohl(net_seq);
        u32 diff =  replay_esn->seq - seq;

        if (!replay_esn->replay_window)
                return 0;

        if (unlikely(seq == 0))
                goto err;

        if (likely(seq > replay_esn->seq))
                return 0;

        if (diff >= replay_esn->replay_window) {
                x->stats.replay_window++;
                goto err;
        }

        pos = (replay_esn->seq - 1) % replay_esn->replay_window;

        if (pos >= diff)
                bitnr = (pos - diff) % replay_esn->replay_window;
        else
                bitnr = replay_esn->replay_window - (diff - pos);

        nr = bitnr >> 5;
        bitnr = bitnr & 0x1F;
        if (replay_esn->bmp[nr] & (1U << bitnr))
                goto err_replay;

        return 0;

err_replay:
        x->stats.replay++;
err:
        xfrm_audit_state_replay(x, skb, net_seq);
        return -EINVAL;
}

static void xfrm_replay_advance_bmp(struct xfrm_state *x, __be32 net_seq)
{
        unsigned int bitnr, nr, i;
        u32 diff;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        u32 seq = ntohl(net_seq);
        u32 pos;

        if (!replay_esn->replay_window)
                return;

        pos = (replay_esn->seq - 1) % replay_esn->replay_window;

        if (seq > replay_esn->seq) {
                diff = seq - replay_esn->seq;

                if (diff < replay_esn->replay_window) {
                        for (i = 1; i < diff; i++) {
                                bitnr = (pos + i) % replay_esn->replay_window;
                                nr = bitnr >> 5;
                                bitnr = bitnr & 0x1F;
                                replay_esn->bmp[nr] &=  ~(1U << bitnr);
                        }
                } else {
                        nr = (replay_esn->replay_window - 1) >> 5;
                        for (i = 0; i <= nr; i++)
                                replay_esn->bmp[i] = 0;
                }

                bitnr = (pos + diff) % replay_esn->replay_window;
                replay_esn->seq = seq;
        } else {
                diff = replay_esn->seq - seq;

                if (pos >= diff)
                        bitnr = (pos - diff) % replay_esn->replay_window;
                else
                        bitnr = replay_esn->replay_window - (diff - pos);
        }

        nr = bitnr >> 5;
        bitnr = bitnr & 0x1F;
        replay_esn->bmp[nr] |= (1U << bitnr);

        if (xfrm_aevent_is_on(xs_net(x)))
                x->repl->notify(x, XFRM_REPLAY_UPDATE);
}

static void xfrm_replay_notify_bmp(struct xfrm_state *x, int event)
{
        struct km_event c;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        struct xfrm_replay_state_esn *preplay_esn = x->preplay_esn;

        /* we send notify messages in case
         *  1. we updated on of the sequence numbers, and the seqno difference
         *     is at least x->replay_maxdiff, in this case we also update the
         *     timeout of our timer function
         *  2. if x->replay_maxage has elapsed since last update,
         *     and there were changes
         *
         *  The state structure must be locked!
         */

        switch (event) {
        case XFRM_REPLAY_UPDATE:
                if (!x->replay_maxdiff ||
                    ((replay_esn->seq - preplay_esn->seq < x->replay_maxdiff) &&
                    (replay_esn->oseq - preplay_esn->oseq
                     < x->replay_maxdiff))) {
                        if (x->xflags & XFRM_TIME_DEFER)
                                event = XFRM_REPLAY_TIMEOUT;
                        else
                                return;
                }

                break;

        case XFRM_REPLAY_TIMEOUT:
                if (memcmp(x->replay_esn, x->preplay_esn,
                           xfrm_replay_state_esn_len(replay_esn)) == 0) {
                        x->xflags |= XFRM_TIME_DEFER;
                        return;
                }

                break;
        }

        memcpy(x->preplay_esn, x->replay_esn,
               xfrm_replay_state_esn_len(replay_esn));
        c.event = XFRM_MSG_NEWAE;
        c.data.aevent = event;
        km_state_notify(x, &c);

        if (x->replay_maxage &&
            !mod_timer(&x->rtimer, jiffies + x->replay_maxage))
                x->xflags &= ~XFRM_TIME_DEFER;
}

static void xfrm_replay_notify_esn(struct xfrm_state *x, int event)
{
        u32 seq_diff, oseq_diff;
        struct km_event c;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        struct xfrm_replay_state_esn *preplay_esn = x->preplay_esn;

        /* we send notify messages in case
         *  1. we updated on of the sequence numbers, and the seqno difference
         *     is at least x->replay_maxdiff, in this case we also update the
         *     timeout of our timer function
         *  2. if x->replay_maxage has elapsed since last update,
         *     and there were changes
         *
         *  The state structure must be locked!
         */

        switch (event) {
        case XFRM_REPLAY_UPDATE:
                if (x->replay_maxdiff) {
                        if (replay_esn->seq_hi == preplay_esn->seq_hi)
                                seq_diff = replay_esn->seq - preplay_esn->seq;
                        else
                                seq_diff = ~preplay_esn->seq + replay_esn->seq
                                           + 1;

                        if (replay_esn->oseq_hi == preplay_esn->oseq_hi)
                                oseq_diff = replay_esn->oseq
                                            - preplay_esn->oseq;
                        else
                                oseq_diff = ~preplay_esn->oseq
                                            + replay_esn->oseq + 1;

                        if (seq_diff >= x->replay_maxdiff ||
                            oseq_diff >= x->replay_maxdiff)
                                break;
                }

                if (x->xflags & XFRM_TIME_DEFER)
                        event = XFRM_REPLAY_TIMEOUT;
                else
                        return;

                break;

        case XFRM_REPLAY_TIMEOUT:
                if (memcmp(x->replay_esn, x->preplay_esn,
                           xfrm_replay_state_esn_len(replay_esn)) == 0) {
                        x->xflags |= XFRM_TIME_DEFER;
                        return;
                }

                break;
        }

        memcpy(x->preplay_esn, x->replay_esn,
               xfrm_replay_state_esn_len(replay_esn));
        c.event = XFRM_MSG_NEWAE;
        c.data.aevent = event;
        km_state_notify(x, &c);

        if (x->replay_maxage &&
            !mod_timer(&x->rtimer, jiffies + x->replay_maxage))
                x->xflags &= ~XFRM_TIME_DEFER;
}

static int xfrm_replay_overflow_esn(struct xfrm_state *x, struct sk_buff *skb)
{
        int err = 0;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        struct net *net = xs_net(x);

        if (x->type->flags & XFRM_TYPE_REPLAY_PROT) {
                XFRM_SKB_CB(skb)->seq.output.low = ++replay_esn->oseq;
                XFRM_SKB_CB(skb)->seq.output.hi = replay_esn->oseq_hi;

                if (unlikely(replay_esn->oseq == 0)) {
                        XFRM_SKB_CB(skb)->seq.output.hi = ++replay_esn->oseq_hi;

                        if (replay_esn->oseq_hi == 0) {
                                replay_esn->oseq--;
                                replay_esn->oseq_hi--;
                                xfrm_audit_state_replay_overflow(x, skb);
                                err = -EOVERFLOW;

                                return err;
                        }
                }
                if (xfrm_aevent_is_on(net))
                        x->repl->notify(x, XFRM_REPLAY_UPDATE);
        }

        return err;
}

static int xfrm_replay_check_esn(struct xfrm_state *x,
                                 struct sk_buff *skb, __be32 net_seq)
{
        unsigned int bitnr, nr;
        u32 diff;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
        u32 pos;
        u32 seq = ntohl(net_seq);
        u32 wsize = replay_esn->replay_window;
        u32 top = replay_esn->seq;
        u32 bottom = top - wsize + 1;

        if (!wsize)
                return 0;

        if (unlikely(seq == 0 && replay_esn->seq_hi == 0 &&
                     (replay_esn->seq < replay_esn->replay_window - 1)))
                goto err;

        diff = top - seq;

        if (likely(top >= wsize - 1)) {
                /* A. same subspace */
                if (likely(seq > top) || seq < bottom)
                        return 0;
        } else {
                /* B. window spans two subspaces */
                if (likely(seq > top && seq < bottom))
                        return 0;
                if (seq >= bottom)
                        diff = ~seq + top + 1;
        }

        if (diff >= replay_esn->replay_window) {
                x->stats.replay_window++;
                goto err;
        }

        pos = (replay_esn->seq - 1) % replay_esn->replay_window;

        if (pos >= diff)
                bitnr = (pos - diff) % replay_esn->replay_window;
        else
                bitnr = replay_esn->replay_window - (diff - pos);

        nr = bitnr >> 5;
        bitnr = bitnr & 0x1F;
        if (replay_esn->bmp[nr] & (1U << bitnr))
                goto err_replay;

        return 0;

err_replay:
        x->stats.replay++;
err:
        xfrm_audit_state_replay(x, skb, net_seq);
        return -EINVAL;
}

static int xfrm_replay_recheck_esn(struct xfrm_state *x,
                                   struct sk_buff *skb, __be32 net_seq)
{
        if (unlikely(XFRM_SKB_CB(skb)->seq.input.hi !=
                     htonl(xfrm_replay_seqhi(x, net_seq)))) {
                        x->stats.replay_window++;
                        return -EINVAL;
        }

        return xfrm_replay_check_esn(x, skb, net_seq);
}

static void xfrm_replay_advance_esn(struct xfrm_state *x, __be32 net_seq)
{
        unsigned int bitnr, nr, i;
        int wrap;
        u32 diff, pos, seq, seq_hi;
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;

        if (!replay_esn->replay_window)
                return;

        seq = ntohl(net_seq);
        pos = (replay_esn->seq - 1) % replay_esn->replay_window;
        seq_hi = xfrm_replay_seqhi(x, net_seq);
        wrap = seq_hi - replay_esn->seq_hi;

        if ((!wrap && seq > replay_esn->seq) || wrap > 0) {
                if (likely(!wrap))
                        diff = seq - replay_esn->seq;
                else
                        diff = ~replay_esn->seq + seq + 1;

                if (diff < replay_esn->replay_window) {
                        for (i = 1; i < diff; i++) {
                                bitnr = (pos + i) % replay_esn->replay_window;
                                nr = bitnr >> 5;
                                bitnr = bitnr & 0x1F;
                                replay_esn->bmp[nr] &=  ~(1U << bitnr);
                        }
                } else {
                        nr = (replay_esn->replay_window - 1) >> 5;
                        for (i = 0; i <= nr; i++)
                                replay_esn->bmp[i] = 0;
                }

                bitnr = (pos + diff) % replay_esn->replay_window;
                replay_esn->seq = seq;

                if (unlikely(wrap > 0))
                        replay_esn->seq_hi++;
        } else {
                diff = replay_esn->seq - seq;

                if (pos >= diff)
                        bitnr = (pos - diff) % replay_esn->replay_window;
                else
                        bitnr = replay_esn->replay_window - (diff - pos);
        }

        nr = bitnr >> 5;
        bitnr = bitnr & 0x1F;
        replay_esn->bmp[nr] |= (1U << bitnr);

        if (xfrm_aevent_is_on(xs_net(x)))
                x->repl->notify(x, XFRM_REPLAY_UPDATE);
}

static struct xfrm_replay xfrm_replay_legacy = {
        .advance        = xfrm_replay_advance,
        .check          = xfrm_replay_check,
        .recheck        = xfrm_replay_check,
        .notify         = xfrm_replay_notify,
        .overflow       = xfrm_replay_overflow,
};

static struct xfrm_replay xfrm_replay_bmp = {
        .advance        = xfrm_replay_advance_bmp,
        .check          = xfrm_replay_check_bmp,
        .recheck        = xfrm_replay_check_bmp,
        .notify         = xfrm_replay_notify_bmp,
        .overflow       = xfrm_replay_overflow_bmp,
};

static struct xfrm_replay xfrm_replay_esn = {
        .advance        = xfrm_replay_advance_esn,
        .check          = xfrm_replay_check_esn,
        .recheck        = xfrm_replay_recheck_esn,
        .notify         = xfrm_replay_notify_esn,
        .overflow       = xfrm_replay_overflow_esn,
};

int xfrm_init_replay(struct xfrm_state *x)
{
        struct xfrm_replay_state_esn *replay_esn = x->replay_esn;

        if (replay_esn) {
                if (replay_esn->replay_window >
                    replay_esn->bmp_len * sizeof(__u32) * 8)
                        return -EINVAL;

                if (x->props.flags & XFRM_STATE_ESN) {
                        if (replay_esn->replay_window == 0)
                                return -EINVAL;
                        x->repl = &xfrm_replay_esn;
                } else
                        x->repl = &xfrm_replay_bmp;
        } else
                x->repl = &xfrm_replay_legacy;

        return 0;
}
EXPORT_SYMBOL(xfrm_init_replay);