xfrm: Support anti-replay window size bigger than 32 packets

As it is, the anti-replay bitmap in struct xfrm_replay_state can
only accomodate 32 packets. Even though it is possible to configure
anti-replay window sizes up to 255 packets from userspace. So we
reject any packet with a sequence number within the configured window
but outside the bitmap. With this patch, we represent the anti-replay
window as a bitmap of variable length that can be accessed via the
new struct xfrm_replay_state_esn. Thus, we have no limit on the
window size anymore. To use the new anti-replay window implementantion,
new userspace tools are required. We leave the old implementation
untouched to stay in sync with old userspace tools.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/xfrm/xfrm_replay.c

 /*
  * 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 <net/xfrm.h>
@@ -125,6 +141,178 @@ static void xfrm_replay_advance(struct xfrm_state *x, __be32 net_seq)
 		xfrm_replay_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 seq = ntohl(net_seq);
+	u32 diff =  replay_esn->seq - seq;
+	u32 pos = (replay_esn->seq - 1) % replay_esn->replay_window;
+
+	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;
+	}
+
+	if (pos >= diff) {
+		bitnr = (pos - diff) % replay_esn->replay_window;
+		nr = bitnr >> 5;
+		bitnr = bitnr & 0x1F;
+		if (replay_esn->bmp[nr] & (1U << bitnr))
+			goto err_replay;
+	} 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 = (replay_esn->seq - 1) % replay_esn->replay_window;
+
+	if (!replay_esn->replay_window)
+		return;
+
+	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);
+			}
+
+			bitnr = (pos + diff) % replay_esn->replay_window;
+			nr = bitnr >> 5;
+			bitnr = bitnr & 0x1F;
+			replay_esn->bmp[nr] |= (1U << bitnr);
+		} else {
+			nr = replay_esn->replay_window >> 5;
+			for (i = 0; i <= nr; i++)
+				replay_esn->bmp[i] = 0;
+
+			bitnr = (pos + diff) % replay_esn->replay_window;
+			nr = bitnr >> 5;
+			bitnr = bitnr & 0x1F;
+			replay_esn->bmp[nr] |= (1U << bitnr);
+		}
+
+		replay_esn->seq = seq;
+	} else {
+		diff = replay_esn->seq - seq;
+
+		if (pos >= diff) {
+			bitnr = (pos - diff) % replay_esn->replay_window;
+			nr = bitnr >> 5;
+			bitnr = bitnr & 0x1F;
+			replay_esn->bmp[nr] |= (1U << bitnr);
+		} 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)))
+		xfrm_replay_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 struct xfrm_replay xfrm_replay_legacy = {
 	.advance	= xfrm_replay_advance,
 	.check		= xfrm_replay_check,
@@ -132,10 +320,27 @@ static struct xfrm_replay xfrm_replay_legacy = {
 	.overflow	= xfrm_replay_overflow,
 };
 
+static struct xfrm_replay xfrm_replay_bmp = {
+	.advance	= xfrm_replay_advance_bmp,
+	.check		= xfrm_replay_check_bmp,
+	.notify		= xfrm_replay_notify_bmp,
+	.overflow	= xfrm_replay_overflow_bmp,
+};
+
 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))
+			return -EINVAL;
+
+		x->repl = &xfrm_replay_bmp;
+	} else
 		x->repl = &xfrm_replay_legacy;
 
+
 	return 0;
 }
 EXPORT_SYMBOL(xfrm_init_replay);