[ipv4] Generalise fragment reassembly mechanism

Generalise the concept of fragment reassembly to allow for code
sharing between IPv4 and IPv6 protocols.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/fragment.h

@@ -0,0 +1,68 @@
+#ifndef _IPXE_FRAGMENT_H
+#define _IPXE_FRAGMENT_H
+
+/** @file
+ *
+ * Fragment reassembly
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <ipxe/list.h>
+#include <ipxe/iobuf.h>
+#include <ipxe/retry.h>
+
+/** Fragment reassembly timeout */
+#define FRAGMENT_TIMEOUT ( TICKS_PER_SEC / 2 )
+
+/** A fragment reassembly buffer */
+struct fragment {
+	/* List of fragment reassembly buffers */
+	struct list_head list;
+	/** Reassembled packet */
+	struct io_buffer *iobuf;
+	/** Length of non-fragmentable portion of reassembled packet */
+	size_t hdrlen;
+	/** Reassembly timer */
+	struct retry_timer timer;
+};
+
+/** A fragment reassembler */
+struct fragment_reassembler {
+	/** List of fragment reassembly buffers */
+	struct list_head list;
+	/**
+	 * Check if fragment matches fragment reassembly buffer
+	 *
+	 * @v fragment		Fragment reassembly buffer
+	 * @v iobuf		I/O buffer
+	 * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+	 * @ret is_fragment	Fragment matches this reassembly buffer
+	 */
+	int ( * is_fragment ) ( struct fragment *fragment,
+				struct io_buffer *iobuf, size_t hdrlen );
+	/**
+	 * Get fragment offset
+	 *
+	 * @v iobuf		I/O buffer
+	 * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+	 * @ret offset		Offset
+	 */
+	size_t ( * fragment_offset ) ( struct io_buffer *iobuf, size_t hdrlen );
+	/**
+	 * Check if more fragments exist
+	 *
+	 * @v iobuf		I/O buffer
+	 * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+	 * @ret more_frags	More fragments exist
+	 */
+	int ( * more_fragments ) ( struct io_buffer *iobuf, size_t hdrlen );
+};
+
+extern struct io_buffer *
+fragment_reassemble ( struct fragment_reassembler *fragments,
+		      struct io_buffer *iobuf, size_t *hdrlen );
+
+#endif /* _IPXE_FRAGMENT_H */

src/include/ipxe/ip.h

@@ -70,18 +70,6 @@ struct ipv4_miniroute {
 	struct in_addr gateway;
 };
 
-/* IPv4 fragment reassembly buffer */
-struct ipv4_fragment {
-	/* List of fragment reassembly buffers */
-	struct list_head list;
-	/** Reassembled packet */
-	struct io_buffer *iobuf;
-	/** Current offset */
-	size_t offset;
-	/** Reassembly timer */
-	struct retry_timer timer;
-};
-
 extern struct list_head ipv4_miniroutes;
 
 extern struct net_protocol ipv4_protocol __net_protocol;

src/net/fragment.c

@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2013 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that 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 Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ipxe/retry.h>
+#include <ipxe/timer.h>
+#include <ipxe/fragment.h>
+
+/** @file
+ *
+ * Fragment reassembly
+ *
+ */
+
+/**
+ * Expire fragment reassembly buffer
+ *
+ * @v timer		Retry timer
+ * @v fail		Failure indicator
+ */
+static void fragment_expired ( struct retry_timer *timer, int fail __unused ) {
+	struct fragment *fragment =
+		container_of ( timer, struct fragment, timer );
+
+	DBGC ( fragment, "FRAG %p expired\n", fragment );
+	free_iob ( fragment->iobuf );
+	list_del ( &fragment->list );
+	free ( fragment );
+}
+
+/**
+ * Find fragment reassembly buffer
+ *
+ * @v fragments		Fragment reassembler
+ * @v iobuf		I/O buffer
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret fragment	Fragment reassembly buffer, or NULL if not found
+ */
+static struct fragment * fragment_find ( struct fragment_reassembler *fragments,
+					 struct io_buffer *iobuf,
+					 size_t hdrlen ) {
+	struct fragment *fragment;
+
+	list_for_each_entry ( fragment, &fragments->list, list ) {
+		if ( fragments->is_fragment ( fragment, iobuf, hdrlen ) )
+			return fragment;
+	}
+	return NULL;
+}
+
+/**
+ * Reassemble packet
+ *
+ * @v fragments		Fragment reassembler
+ * @v iobuf		I/O buffer
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret iobuf		Reassembled packet, or NULL
+ *
+ * This function takes ownership of the I/O buffer.  Note that the
+ * length of the non-fragmentable portion may be modified.
+ */
+struct io_buffer * fragment_reassemble ( struct fragment_reassembler *fragments,
+					 struct io_buffer *iobuf,
+					 size_t *hdrlen ) {
+	struct fragment *fragment;
+	struct io_buffer *new_iobuf;
+	size_t new_len;
+	size_t offset;
+	size_t expected_offset;
+	int more_frags;
+
+	/* Find matching fragment reassembly buffer, if any */
+	fragment = fragment_find ( fragments, iobuf, *hdrlen );
+
+	/* Drop out-of-order fragments */
+	offset = fragments->fragment_offset ( iobuf, *hdrlen );
+	expected_offset = ( fragment ? ( iob_len ( fragment->iobuf ) -
+					 fragment->hdrlen ) : 0 );
+	if ( offset != expected_offset ) {
+		DBGC ( fragment, "FRAG %p dropping out-of-sequence fragment "
+		       "[%zd,%zd), expected [%zd,...)\n", fragment, offset,
+		       ( offset + iob_len ( iobuf ) - *hdrlen ),
+		       expected_offset );
+		goto drop;
+	}
+
+	/* Create or extend fragment reassembly buffer as applicable */
+	if ( ! fragment ) {
+
+		/* Create new fragment reassembly buffer */
+		fragment = zalloc ( sizeof ( *fragment ) );
+		if ( ! fragment )
+			goto drop;
+		list_add ( &fragment->list, &fragments->list );
+		fragment->iobuf = iobuf;
+		fragment->hdrlen = *hdrlen;
+		timer_init ( &fragment->timer, fragment_expired, NULL );
+		DBGC ( fragment, "FRAG %p [0,%zd)\n", fragment,
+		       ( iob_len ( iobuf ) - *hdrlen ) );
+
+	} else {
+
+		/* Check if this is the final fragment */
+		more_frags = fragments->more_fragments ( iobuf, *hdrlen );
+		DBGC ( fragment, "FRAG %p [%zd,%zd)%s\n", fragment,
+		       offset, ( offset + iob_len ( iobuf ) - *hdrlen ),
+		       ( more_frags ? "" : " complete" ) );
+
+		/* Extend fragment reassembly buffer.  Preserve I/O
+		 * buffer headroom to allow for code which modifies
+		 * and resends the buffer (e.g. ICMP echo responses).
+		 */
+		iob_pull ( iobuf, *hdrlen );
+		new_len = ( iob_headroom ( fragment->iobuf ) +
+			    iob_len ( fragment->iobuf ) + iob_len ( iobuf ) );
+		new_iobuf = alloc_iob ( new_len );
+		if ( ! new_iobuf ) {
+			DBGC ( fragment, "FRAG %p could not extend reassembly "
+			       "buffer to %zd bytes\n", fragment, new_len );
+			goto drop;
+		}
+		iob_reserve ( new_iobuf, iob_headroom ( fragment->iobuf ) );
+		memcpy ( iob_put ( new_iobuf, iob_len ( fragment->iobuf ) ),
+			 fragment->iobuf->data, iob_len ( fragment->iobuf ) );
+		memcpy ( iob_put ( new_iobuf, iob_len ( iobuf ) ),
+			 iobuf->data, iob_len ( iobuf ) );
+		free_iob ( fragment->iobuf );
+		fragment->iobuf = new_iobuf;
+		free_iob ( iobuf );
+
+		/* Stop fragment reassembly timer */
+		stop_timer ( &fragment->timer );
+
+		/* If this is the final fragment, return it */
+		if ( ! more_frags ) {
+			iobuf = fragment->iobuf;
+			*hdrlen = fragment->hdrlen;
+			list_del ( &fragment->list );
+			free ( fragment );
+			return iobuf;
+		}
+	}
+
+	/* (Re)start fragment reassembly timer */
+	start_timer_fixed ( &fragment->timer, FRAGMENT_TIMEOUT );
+
+	return NULL;
+
+ drop:
+	free_iob ( iobuf );
+	return NULL;
+}

src/net/ipv4.c

@@ -14,7 +14,7 @@
 #include <ipxe/tcpip.h>
 #include <ipxe/dhcp.h>
 #include <ipxe/settings.h>
-#include <ipxe/timer.h>
+#include <ipxe/fragment.h>
 
 /** @file
  *
@@ -30,12 +30,6 @@ static uint8_t next_ident_high = 0;
 /** List of IPv4 miniroutes */
 struct list_head ipv4_miniroutes = LIST_HEAD_INIT ( ipv4_miniroutes );
 
-/** List of fragment reassembly buffers */
-static LIST_HEAD ( ipv4_fragments );
-
-/** Fragment reassembly timeout */
-#define IP_FRAG_TIMEOUT ( TICKS_PER_SEC / 2 )
-
 /**
  * Add IPv4 minirouting table entry
  *
@@ -133,131 +127,59 @@ static struct ipv4_miniroute * ipv4_route ( struct in_addr *dest ) {
 }
 
 /**
- * Expire fragment reassembly buffer
+ * Check if IPv4 fragment matches fragment reassembly buffer
  *
- * @v timer		Retry timer
- * @v fail		Failure indicator
+ * @v fragment		Fragment reassembly buffer
+ * @v iobuf		I/O buffer
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret is_fragment	Fragment matches this reassembly buffer
  */
-static void ipv4_fragment_expired ( struct retry_timer *timer,
-				    int fail __unused ) {
-	struct ipv4_fragment *frag =
-		container_of ( timer, struct ipv4_fragment, timer );
-	struct iphdr *iphdr = frag->iobuf->data;
-
-	DBGC ( iphdr->src, "IPv4 fragment %04x expired\n",
-	       ntohs ( iphdr->ident ) );
-	free_iob ( frag->iobuf );
-	list_del ( &frag->list );
-	free ( frag );
+static int ipv4_is_fragment ( struct fragment *fragment,
+			      struct io_buffer *iobuf,
+			      size_t hdrlen __unused ) {
+	struct iphdr *frag_iphdr = fragment->iobuf->data;
+	struct iphdr *iphdr = iobuf->data;
+
+	return ( ( iphdr->src.s_addr == frag_iphdr->src.s_addr ) &&
+		 ( iphdr->ident == frag_iphdr->ident ) );
 }
 
 /**
- * Find matching fragment reassembly buffer
+ * Get IPv4 fragment offset
  *
- * @v iphdr		IPv4 header
- * @ret frag		Fragment reassembly buffer, or NULL
+ * @v iobuf		I/O buffer
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret offset		Offset
  */
-static struct ipv4_fragment * ipv4_fragment ( struct iphdr *iphdr ) {
-	struct ipv4_fragment *frag;
-	struct iphdr *frag_iphdr;
-
-	list_for_each_entry ( frag, &ipv4_fragments, list ) {
-		frag_iphdr = frag->iobuf->data;
-
-		if ( ( iphdr->src.s_addr == frag_iphdr->src.s_addr ) &&
-		     ( iphdr->ident == frag_iphdr->ident ) ) {
-			return frag;
-		}
-	}
+static size_t ipv4_fragment_offset ( struct io_buffer *iobuf,
+				     size_t hdrlen __unused ) {
+	struct iphdr *iphdr = iobuf->data;
 
-	return NULL;
+	return ( ( ntohs ( iphdr->frags ) & IP_MASK_OFFSET ) << 3 );
 }
 
 /**
- * Fragment reassembler
+ * Check if more fragments exist
  *
  * @v iobuf		I/O buffer
- * @ret iobuf		Reassembled packet, or NULL
+ * @v hdrlen		Length of non-fragmentable potion of I/O buffer
+ * @ret more_frags	More fragments exist
  */
-static struct io_buffer * ipv4_reassemble ( struct io_buffer *iobuf ) {
+static int ipv4_more_fragments ( struct io_buffer *iobuf,
+				 size_t hdrlen __unused ) {
 	struct iphdr *iphdr = iobuf->data;
-	size_t offset = ( ( ntohs ( iphdr->frags ) & IP_MASK_OFFSET ) << 3 );
-	unsigned int more_frags = ( iphdr->frags & htons ( IP_MASK_MOREFRAGS ));
-	size_t hdrlen = ( ( iphdr->verhdrlen & IP_MASK_HLEN ) * 4 );
-	struct ipv4_fragment *frag;
-	size_t expected_offset;
-	struct io_buffer *new_iobuf;
-
-	/* Find matching fragment reassembly buffer, if any */
-	frag = ipv4_fragment ( iphdr );
-
-	/* Drop out-of-order fragments */
-	expected_offset = ( frag ? frag->offset : 0 );
-	if ( offset != expected_offset ) {
-		DBGC ( iphdr->src, "IPv4 dropping out-of-sequence fragment "
-		       "%04x (%zd+%zd, expected %zd)\n",
-		       ntohs ( iphdr->ident ), offset,
-		      ( iob_len ( iobuf ) - hdrlen ), expected_offset );
-		goto drop;
-	}
-
-	/* Create or extend fragment reassembly buffer as applicable */
-	if ( frag == NULL ) {
 
-		/* Create new fragment reassembly buffer */
-		frag = zalloc ( sizeof ( *frag ) );
-		if ( ! frag )
-			goto drop;
-		list_add ( &frag->list, &ipv4_fragments );
-		frag->iobuf = iobuf;
-		frag->offset = ( iob_len ( iobuf ) - hdrlen );
-		timer_init ( &frag->timer, ipv4_fragment_expired, NULL );
-
-	} else {
-
-		/* Extend reassembly buffer */
-		iob_pull ( iobuf, hdrlen );
-		new_iobuf = alloc_iob ( iob_len ( frag->iobuf ) +
-					iob_len ( iobuf ) );
-		if ( ! new_iobuf ) {
-			DBGC ( iphdr->src, "IPv4 could not extend reassembly "
-			       "buffer to %zd bytes\n",
-			       iob_len ( frag->iobuf ) + iob_len ( iobuf ) );
-			goto drop;
-		}
-		memcpy ( iob_put ( new_iobuf, iob_len ( frag->iobuf ) ),
-			 frag->iobuf->data, iob_len ( frag->iobuf ) );
-		memcpy ( iob_put ( new_iobuf, iob_len ( iobuf ) ),
-			 iobuf->data, iob_len ( iobuf ) );
-		free_iob ( frag->iobuf );
-		frag->iobuf = new_iobuf;
-		frag->offset += iob_len ( iobuf );
-		free_iob ( iobuf );
-		iphdr = frag->iobuf->data;
-		iphdr->len = ntohs ( iob_len ( frag->iobuf ) );
-
-		/* Stop fragment reassembly timer */
-		stop_timer ( &frag->timer );
-
-		/* If this is the final fragment, return it */
-		if ( ! more_frags ) {
-			iobuf = frag->iobuf;
-			list_del ( &frag->list );
-			free ( frag );
-			return iobuf;
-		}
-	}
-
-	/* (Re)start fragment reassembly timer */
-	start_timer_fixed ( &frag->timer, IP_FRAG_TIMEOUT );
-
-	return NULL;
-
- drop:
-	free_iob ( iobuf );
-	return NULL;
+	return ( iphdr->frags & htons ( IP_MASK_MOREFRAGS ) );
 }
 
+/** IPv4 fragment reassembler */
+static struct fragment_reassembler ipv4_reassembler = {
+	.list = LIST_HEAD_INIT ( ipv4_reassembler.list ),
+	.is_fragment = ipv4_is_fragment,
+	.fragment_offset = ipv4_fragment_offset,
+	.more_fragments = ipv4_more_fragments,
+};
+
 /**
  * Add IPv4 pseudo-header checksum to existing checksum
  *
@@ -526,14 +448,14 @@ static int ipv4_rx ( struct io_buffer *iobuf,
 
 	/* Perform fragment reassembly if applicable */
 	if ( iphdr->frags & htons ( IP_MASK_OFFSET | IP_MASK_MOREFRAGS ) ) {
-		/* Pass the fragment to ipv4_reassemble() which returns
+		/* Pass the fragment to fragment_reassemble() which returns
 		 * either a fully reassembled I/O buffer or NULL.
 		 */
-		iobuf = ipv4_reassemble ( iobuf );
+		iobuf = fragment_reassemble ( &ipv4_reassembler, iobuf,
+					      &hdrlen );
 		if ( ! iobuf )
 			return 0;
 		iphdr = iobuf->data;
-		hdrlen = ( ( iphdr->verhdrlen & IP_MASK_HLEN ) * 4 );
 	}
 
 	/* Construct socket addresses, calculate pseudo-header