pf: Count holes rather than fragments for reassembly

Avoid traversing the list of fragment entris to check whether the
pf(4) reassembly is complete.  Instead count the holes that are
created when inserting a fragment.  If there are no holes left, the
fragments are continuous.

Obtained from:	OpenBSD
Differential Revision:	https://reviews.freebsd.org/D17732

(cherry picked from commit 2b1c354ee6fb075953d2c3e81c8221f4115ce981)

1 files changed, 45 insertions, 38 deletions

diff --git a/sys/netpfil/pf/pf_norm.c b/sys/netpfil/pf/pf_norm.c
index cadc7a73dca4..cd94d1de7cf7 100644
--- a/sys/netpfil/pf/pf_norm.c
+++ b/sys/netpfil/pf/pf_norm.c
@@ -2,7 +2,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright 2001 Niels Provos <provos@citi.umich.edu>
- * Copyright 2011 Alexander Bluhm <bluhm@openbsd.org>
+ * Copyright 2011-2018 Alexander Bluhm <bluhm@openbsd.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -91,6 +91,7 @@ struct pf_fragment {
 	TAILQ_ENTRY(pf_fragment) frag_next;
 	uint32_t	fr_timeout;
 	uint16_t	fr_maxlen;	/* maximum length of single fragment */
+	u_int16_t	fr_holes;	/* number of holes in the queue */
 	TAILQ_HEAD(pf_fragq, pf_frent) fr_queue;
 };
 
@@ -132,11 +133,11 @@ static void	pf_remove_fragment(struct pf_fragment *);
 static int	pf_normalize_tcpopt(struct pf_krule *, struct mbuf *,
 		    struct tcphdr *, int, sa_family_t);
 static struct pf_frent *pf_create_fragment(u_short *);
+static int	pf_frent_holes(struct pf_frent *frent);
 static struct pf_fragment *pf_find_fragment(struct pf_fragment_cmp *key,
 		    struct pf_frag_tree *tree);
 static struct pf_fragment *pf_fillup_fragment(struct pf_fragment_cmp *,
 		    struct pf_frent *, u_short *);
-static int	pf_isfull_fragment(struct pf_fragment *);
 static struct mbuf *pf_join_fragment(struct pf_fragment *);
 #ifdef INET
 static void	pf_scrub_ip(struct mbuf **, uint32_t, uint8_t, uint8_t);
@@ -333,6 +334,39 @@ pf_create_fragment(u_short *reason)
 	return (frent);
 }
 
+/*
+ * Calculate the additional holes that were created in the fragment
+ * queue by inserting this fragment.  A fragment in the middle
+ * creates one more hole by splitting.  For each connected side,
+ * it loses one hole.
+ * Fragment entry must be in the queue when calling this function.
+ */
+static int
+pf_frent_holes(struct pf_frent *frent)
+{
+	struct pf_frent *prev = TAILQ_PREV(frent, pf_fragq, fr_next);
+	struct pf_frent *next = TAILQ_NEXT(frent, fr_next);
+	int holes = 1;
+
+	if (prev == NULL) {
+		if (frent->fe_off == 0)
+			holes--;
+	} else {
+		KASSERT(frent->fe_off != 0, ("frent->fe_off != 0"));
+		if (frent->fe_off == prev->fe_off + prev->fe_len)
+			holes--;
+	}
+	if (next == NULL) {
+		if (!frent->fe_mff)
+			holes--;
+	} else {
+		KASSERT(frent->fe_mff, ("frent->fe_mff"));
+		if (next->fe_off == frent->fe_off + frent->fe_len)
+			holes--;
+	}
+	return holes;
+}
+
 static struct pf_fragment *
 pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 		u_short *reason)
@@ -384,6 +418,7 @@ pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 		*(struct pf_fragment_cmp *)frag = *key;
 		frag->fr_timeout = time_uptime;
 		frag->fr_maxlen = frent->fe_len;
+		frag->fr_holes = 1;
 		TAILQ_INIT(&frag->fr_queue);
 
 		RB_INSERT(pf_frag_tree, &V_pf_frag_tree, frag);
@@ -391,6 +426,7 @@ pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 
 		/* We do not have a previous fragment. */
 		TAILQ_INSERT_HEAD(&frag->fr_queue, frent, fr_next);
+		frag->fr_holes += pf_frent_holes(frent);
 
 		return (frag);
 	}
@@ -457,6 +493,7 @@ pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 
 		/* This fragment is completely overlapped, lose it. */
 		next = TAILQ_NEXT(after, fr_next);
+		frag->fr_holes -= pf_frent_holes(after);
 		m_freem(after->fe_m);
 		TAILQ_REMOVE(&frag->fr_queue, after, fr_next);
 		uma_zfree(V_pf_frent_z, after);
@@ -466,6 +503,7 @@ pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 		TAILQ_INSERT_HEAD(&frag->fr_queue, frent, fr_next);
 	else
 		TAILQ_INSERT_AFTER(&frag->fr_queue, prev, frent, fr_next);
+	frag->fr_holes += pf_frent_holes(frent);
 
 	return (frag);
 
@@ -476,40 +514,6 @@ drop_fragment:
 	return (NULL);
 }
 
-static int
-pf_isfull_fragment(struct pf_fragment *frag)
-{
-	struct pf_frent	*frent, *next;
-	uint16_t off, total;
-
-	/* Check if we are completely reassembled */
-	if (TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_mff)
-		return (0);
-
-	/* Maximum data we have seen already */
-	total = TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_off +
-		TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_len;
-
-	/* Check if we have all the data */
-	off = 0;
-	for (frent = TAILQ_FIRST(&frag->fr_queue); frent; frent = next) {
-		next = TAILQ_NEXT(frent, fr_next);
-
-		off += frent->fe_len;
-		if (off < total && (next == NULL || next->fe_off != off)) {
-			DPFPRINTF(("missing fragment at %d, next %d, total %d",
-			    off, next == NULL ? -1 : next->fe_off, total));
-			return (0);
-		}
-	}
-	DPFPRINTF(("%d < %d?", off, total));
-	if (off < total)
-		return (0);
-	KASSERT(off == total, ("off == total"));
-
-	return (1);
-}
-
 static struct mbuf *
 pf_join_fragment(struct pf_fragment *frag)
 {
@@ -570,8 +574,10 @@ pf_reassemble(struct mbuf **m0, struct ip *ip, int dir, u_short *reason)
 	/* The mbuf is part of the fragment entry, no direct free or access */
 	m = *m0 = NULL;
 
-	if (!pf_isfull_fragment(frag))
+	if (frag->fr_holes) {
+		DPFPRINTF(("frag %d, holes %d", frag->fr_id, frag->fr_holes));
 		return (PF_PASS);  /* drop because *m0 is NULL, no error */
+	}
 
 	/* We have all the data */
 	frent = TAILQ_FIRST(&frag->fr_queue);
@@ -654,7 +660,8 @@ pf_reassemble6(struct mbuf **m0, struct ip6_hdr *ip6, struct ip6_frag *fraghdr,
 	/* The mbuf is part of the fragment entry, no direct free or access. */
 	m = *m0 = NULL;
 
-	if (!pf_isfull_fragment(frag)) {
+	if (frag->fr_holes) {
+		DPFPRINTF(("frag %d, holes %d", frag->fr_id, frag->fr_holes));
 		PF_FRAG_UNLOCK();
 		return (PF_PASS);  /* Drop because *m0 is NULL, no error. */
 	}