Add an accept filter for TCP based DNS requests. It waits until the

whole first request is present before returning from accept.

sys/boot/forth/loader.conf

@@ -391,6 +391,7 @@ bktr_load="NO"			# Brooktree Bt848/Bt878 TV/Video Capture Card
 ispfw_load="NO"			# Qlogic ISP Firmware
 agp_load="NO"			# agp module
 accf_data_load="NO"		# Wait for data accept filter
+accf_dns_load="NO"		# Wait for data accept filter
 accf_http_load="NO"		# Wait for full HTTP request accept filter
 random_load="NO"		# Random device
 speaker_load="NO"		# AT speaker module

sys/conf/NOTES

@@ -887,6 +887,7 @@ options		MBUF_PROFILING
 
 # Statically Link in accept filters
 options 	ACCEPT_FILTER_DATA
+options 	ACCEPT_FILTER_DNS
 options 	ACCEPT_FILTER_HTTP
 
 # TCP_SIGNATURE adds support for RFC 2385 (TCP-MD5) digests. These are

sys/conf/files

@@ -1902,6 +1902,7 @@ netgraph/ng_tee.c		optional netgraph_tee
 netgraph/ng_tty.c		optional netgraph_tty
 netgraph/ng_vjc.c		optional netgraph_vjc
 netinet/accf_data.c		optional accept_filter_data
+netinet/accf_dns.c		optional accept_filter_dns
 netinet/accf_http.c		optional accept_filter_http
 netinet/if_atm.c		optional atm
 netinet/if_ether.c		optional ether

sys/conf/options

@@ -342,6 +342,7 @@ ATA_NOPCI		opt_ata.h
 
 # Net stuff.
 ACCEPT_FILTER_DATA
+ACCEPT_FILTER_DNS
 ACCEPT_FILTER_HTTP
 ALTQ			opt_global.h
 ALTQ_CBQ		opt_altq.h

sys/modules/Makefile

@@ -6,6 +6,7 @@ SUBDIR=	${_3dfx} \
 	${_3dfx_linux} \
 	${_aac} \
 	accf_data \
+	accf_dns \
 	accf_http \
 	${_acpi} \
 	age \

sys/modules/accf_dns/Makefile

@@ -0,0 +1,8 @@
+# $FreeBSD$
+
+.PATH: ${.CURDIR}/../../netinet
+
+KMOD=	accf_dns
+SRCS=	accf_dns.c
+
+.include <bsd.kmod.mk>

sys/netinet/accf_dns.c

@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2007 David Malone <dwmalone@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	$FreeBSD$
+ */
+
+#define ACCEPT_FILTER_MOD
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/mbuf.h>
+#include <sys/module.h>
+#include <sys/signalvar.h>
+#include <sys/sysctl.h>
+#include <sys/socketvar.h>
+
+/* check for full DNS request */
+static void sohasdns(struct socket *so, void *arg, int waitflag);
+
+struct packet {
+	struct mbuf *m;		/* Current mbuf. */
+	struct mbuf *n;		/* nextpkt mbuf. */
+	unsigned long moff;	/* Offset of the beginning of m. */
+	unsigned long offset;	/* Which offset we are working at. */
+	unsigned long len;	/* The number of bytes we have to play with. */
+};
+
+#define DNS_OK 0
+#define DNS_WAIT -1
+#define DNS_RUN -2
+
+/* check we can skip over various parts of DNS request */
+static int skippacket(struct sockbuf *sb);
+
+static struct accept_filter accf_dns_filter = {
+	"dnsready",
+	sohasdns,
+	NULL,
+	NULL
+};
+
+static moduledata_t accf_dns_mod = {
+	"accf_dns",
+	accept_filt_generic_mod_event,
+	&accf_dns_filter
+};
+
+DECLARE_MODULE(accf_dns, accf_dns_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);
+
+static void
+sohasdns(struct socket *so, void *arg, int waitflag)
+{
+	struct sockbuf *sb = &so->so_rcv;
+
+	/* If the socket is full, we're ready. */
+	if (sb->sb_cc >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax)
+		goto ready;
+
+	/* Check and see if we have a request. */
+	if (skippacket(sb) == DNS_WAIT)
+		return;
+
+ready:
+	so->so_upcall = NULL;
+	so->so_rcv.sb_flags &= ~SB_UPCALL;
+	soisconnected(so);
+	return;
+}
+
+#define GET8(p, val) do { \
+	if (p->offset < p->moff) \
+		return DNS_RUN; \
+	while (p->offset >= p->moff + p->m->m_len) { \
+		p->moff += p->m->m_len; \
+		p->m = p->m->m_next; \
+		if (p->m == NULL) { \
+			p->m = p->n; \
+			p->n = p->m->m_nextpkt; \
+		} \
+		if (p->m == NULL) \
+			return DNS_WAIT; \
+	} \
+	val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \
+	p->offset++; \
+	} while (0)
+
+#define GET16(p, val) do { \
+	unsigned int v0, v1; \
+	GET8(p, v0); \
+	GET8(p, v1); \
+	val = v0 * 0x100 + v1; \
+	} while (0)
+
+static int
+skippacket(struct sockbuf *sb) {
+	unsigned long packlen;
+	struct packet q, *p = &q;
+
+	if (sb->sb_cc < 2)
+		return DNS_WAIT;
+
+	q.m = sb->sb_mb;
+	q.n = q.m->m_nextpkt;
+	q.moff = 0;
+	q.offset = 0;
+	q.len = sb->sb_cc;
+
+	GET16(p, packlen);
+	if (packlen + 2 < q.len)
+		return DNS_WAIT;
+
+	return DNS_OK;
+}