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Add packet-dump debugging facility.

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This commit is contained in:
Simon Kelley 2018-05-08 18:32:14 +01:00
parent 07ed585c38
commit 6b17335209
10 changed files with 329 additions and 11 deletions
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6
CHANGELOG
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@ -17,6 +17,12 @@ version 2.80
Fix DHCP broken-ness when --no-ping AND --dhcp-sequential-ip
are set. Thanks to Daniel Miess for help with this.
Add a facilty to store DNS packets sent/recieved in a
pcap-format file for later debugging. The file location
is given by the --dumpfile option, and a bitmap controlling
which packets should be dumped is given by the --dumpmask
option.
version 2.79
Fix parsing of CNAME arguments, which are confused by extra spaces.

2
Makefile
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@ -76,7 +76,7 @@ objs = cache.o rfc1035.o util.o option.o forward.o network.o \
helper.o tftp.o log.o conntrack.o dhcp6.o rfc3315.o \
dhcp-common.o outpacket.o radv.o slaac.o auth.o ipset.o \
domain.o dnssec.o blockdata.o tables.o loop.o inotify.o \
poll.o rrfilter.o edns0.o arp.o crypto.o
poll.o rrfilter.o edns0.o arp.o crypto.o dump.o
hdrs = dnsmasq.h config.h dhcp-protocol.h dhcp6-protocol.h \
dns-protocol.h radv-protocol.h ip6addr.h

3
bld/Android.mk
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@ -10,7 +10,8 @@ LOCAL_SRC_FILES := bpf.c cache.c dbus.c dhcp.c dnsmasq.c \
dhcp6.c rfc3315.c dhcp-common.c outpacket.c \
radv.c slaac.c auth.c ipset.c domain.c \
dnssec.c dnssec-openssl.c blockdata.c tables.c \
loop.c inotify.c poll.c rrfilter.c edns0.c arp.c crypto.c
loop.c inotify.c poll.c rrfilter.c edns0.c arp.c \
crypto.c dump.c
LOCAL_MODULE := dnsmasq

7
man/dnsmasq.8
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@ -647,6 +647,13 @@ V4 mapped IPv6 addresses, which have a representation like ::ffff:1.2.3.4 are ha
The address range can be of the form
<ip address>,<ip address> or <ip address>/<netmask> in both forms of the option.
.TP
.B --dumpfile=<path/to/file>
Specify the location of a pcap-format file which dnsmasq uses to dump copies of network packets for debugging purposes. If the file exists when dnsmasq starts, it is not deleted; new packets are added to the end.
.TP
.B --dumpmask=<mask>
Specify which types of packets should be added to the dumpfile. The argument should be the OR of the bitmasks for each type of packet to be dumped: it can be specified in hex by preceding the number with 0x in the normal way. Each time a packet is written to the dumpfile, dnsmasq logs the packet sequence and the mask
representing its type. The current types are: 0x0001 - DNS queries from clients 0x0002 DNS replies to clients 0x0004 - DNS queries to upstream 0x0008 - DNS replies from upstream 0x0010 - queries send upstream for DNSSEC validation 0x0020 - replies to queries for DNSSEC validation 0x0040 - replies to client queries which fail DNSSEC validation 0x0080 replies to queries for DNSSEC validation which fail validation.
.TP
.B --add-mac[=base64|text]
Add the MAC address of the requestor to DNS queries which are
forwarded upstream. This may be used to DNS filtering by the upstream

16
src/config.h
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@ -117,6 +117,9 @@ HAVE_AUTH
HAVE_DNSSEC
include DNSSEC validator.
HAVE_DUMPFILE
include code to dump packets to a libpcap-format file for debugging.
HAVE_LOOP
include functionality to probe for and remove DNS forwarding loops.
@ -132,6 +135,7 @@ NO_DHCP6
NO_SCRIPT
NO_LARGEFILE
NO_AUTH
NO_DUMPFILE
NO_INOTIFY
these are available to explicitly disable compile time options which would
otherwise be enabled automatically (HAVE_IPV6, >2Gb file sizes) or
@ -164,6 +168,7 @@ RESOLVFILE
#define HAVE_AUTH
#define HAVE_IPSET
#define HAVE_LOOP
#define HAVE_DUMPFILE
/* Build options which require external libraries.
@ -363,6 +368,10 @@ HAVE_SOCKADDR_SA_LEN
#undef HAVE_LOOP
#endif
#ifdef NO_DUMPFILE
#undef HAVE_DUMPFILE
#endif
#if defined (HAVE_LINUX_NETWORK) && !defined(NO_INOTIFY)
#define HAVE_INOTIFY
#endif
@ -451,8 +460,11 @@ static char *compile_opts =
#ifndef HAVE_INOTIFY
"no-"
#endif
"inotify";
"inotify "
#ifndef HAVE_DUMPFILE
"no-"
#endif
"dumpfile";
#endif

16
src/dnsmasq.c
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@ -366,7 +366,16 @@ int main (int argc, char **argv)
else
daemon->inotifyfd = -1;
#endif
if (daemon->dump_file)
#ifdef HAVE_DUMPFILE
dump_init();
else
daemon->dumpfd = -1;
#else
die(_("Packet dumps not available: set HAVE_DUMP in src/config.h"), NULL, EC_BADCONF);
#endif
if (option_bool(OPT_DBUS))
#ifdef HAVE_DBUS
{
@ -1424,6 +1433,11 @@ static void async_event(int pipe, time_t now)
if (daemon->runfile)
unlink(daemon->runfile);
#ifdef HAVE_DUMPFILE
if (daemon->dumpfd != -1)
close(daemon->dumpfd);
#endif
my_syslog(LOG_INFO, _("exiting on receipt of SIGTERM"));
flush_log();

29
src/dnsmasq.h
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@ -119,6 +119,9 @@ typedef unsigned long long u64;
#include <net/if_arp.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#ifdef HAVE_IPV6
#include <netinet/ip6.h>
#endif
#include <netinet/ip_icmp.h>
#include <sys/uio.h>
#include <syslog.h>
@ -598,6 +601,16 @@ struct hostsfile {
unsigned int index; /* matches to cache entries for logging */
};
/* packet-dump flags */
#define DUMP_QUERY 0x0001
#define DUMP_REPLY 0x0002
#define DUMP_UP_QUERY 0x0004
#define DUMP_UP_REPLY 0x0008
#define DUMP_SEC_QUERY 0x0010
#define DUMP_SEC_REPLY 0x0020
#define DUMP_BOGUS 0x0040
#define DUMP_SEC_BOGUS 0x0080
/* DNSSEC status values. */
#define STAT_SECURE 1
@ -1020,14 +1033,14 @@ extern struct daemon {
unsigned int duid_enterprise, duid_config_len;
unsigned char *duid_config;
char *dbus_name;
char *dump_file;
int dump_mask;
unsigned long soa_sn, soa_refresh, soa_retry, soa_expiry;
#ifdef OPTION6_PREFIX_CLASS
struct prefix_class *prefix_classes;
#endif
#ifdef HAVE_DNSSEC
struct ds_config *ds;
int dnssec_no_time_check;
int back_to_the_future;
char *timestamp_file;
#endif
@ -1040,6 +1053,8 @@ extern struct daemon {
char *workspacename; /* ditto */
char *rr_status; /* flags for individual RRs */
int rr_status_sz;
int dnssec_no_time_check;
int back_to_the_future;
#endif
unsigned int local_answer, queries_forwarded, auth_answer;
struct frec *frec_list;
@ -1094,6 +1109,10 @@ extern struct daemon {
char *addrbuff;
char *addrbuff2; /* only allocated when OPT_EXTRALOG */
#ifdef HAVE_DUMPFILE
/* file for packet dumps. */
int dumpfd;
#endif
} *daemon;
/* cache.c */
@ -1588,3 +1607,9 @@ int check_source(struct dns_header *header, size_t plen, unsigned char *pseudohe
/* arp.c */
int find_mac(union mysockaddr *addr, unsigned char *mac, int lazy, time_t now);
int do_arp_script_run(void);
/* dump.c */
#ifdef HAVE_DUMPFILE
void dump_init(void);
void dump_packet(int mask, void *packet, size_t len, union mysockaddr *src, union mysockaddr *dst);
#endif

210
src/dump.c Normal file
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@ -0,0 +1,210 @@
/* dnsmasq is Copyright (c) 2000-2018 Simon Kelley
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; version 2 dated June, 1991, or
(at your option) version 3 dated 29 June, 2007.
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, see <http://www.gnu.org/licenses/>.
*/
#include "dnsmasq.h"
#ifdef HAVE_DUMPFILE
static u32 packet_count;
/* https://wiki.wireshark.org/Development/LibpcapFileFormat */
struct pcap_hdr_s {
u32 magic_number; /* magic number */
u16 version_major; /* major version number */
u16 version_minor; /* minor version number */
u32 thiszone; /* GMT to local correction */
u32 sigfigs; /* accuracy of timestamps */
u32 snaplen; /* max length of captured packets, in octets */
u32 network; /* data link type */
};
struct pcaprec_hdr_s {
u32 ts_sec; /* timestamp seconds */
u32 ts_usec; /* timestamp microseconds */
u32 incl_len; /* number of octets of packet saved in file */
u32 orig_len; /* actual length of packet */
};
void dump_init(void)
{
struct stat buf;
struct pcap_hdr_s header;
struct pcaprec_hdr_s pcap_header;
packet_count = 0;
if (stat(daemon->dump_file, &buf) == -1)
{
/* doesn't exist, create and add header */
header.magic_number = 0xa1b2c3d4;
header.version_major = 2;
header.version_minor = 4;
header.thiszone = 0;
header.sigfigs = 0;
header.snaplen = daemon->edns_pktsz + 200; /* slop for IP/UDP headers */
header.network = 101; /* DLT_RAW http://www.tcpdump.org/linktypes.html */
if (errno != ENOENT ||
(daemon->dumpfd = creat(daemon->dump_file, S_IRUSR | S_IWUSR)) == -1 ||
!read_write(daemon->dumpfd, (void *)&header, sizeof(header), 0))
die(_("cannot create %s: %s"), daemon->dump_file, EC_FILE);
}
else if ((daemon->dumpfd = open(daemon->dump_file, O_APPEND | O_RDWR)) == -1 ||
!read_write(daemon->dumpfd, (void *)&header, sizeof(header), 1) ||
header.magic_number != 0xa1b2c3d4)
die(_("cannot access %s: %s"), daemon->dump_file, EC_FILE);
else
{
/* count existing records */
while (read_write(daemon->dumpfd, (void *)&pcap_header, sizeof(pcap_header), 1))
{
lseek(daemon->dumpfd, pcap_header.incl_len, SEEK_CUR);
packet_count++;
}
}
}
void dump_packet(int mask, void *packet, size_t len, union mysockaddr *src, union mysockaddr *dst)
{
struct ip ip;
#ifdef HAVE_IPV6
struct ip6_hdr ip6;
int family;
#endif
struct udphdr {
u16 uh_sport; /* source port */
u16 uh_dport; /* destination port */
u16 uh_ulen; /* udp length */
u16 uh_sum; /* udp checksum */
} udp;
struct pcaprec_hdr_s pcap_header;
struct timeval time;
u32 i, sum;
void *iphdr;
size_t ipsz;
int rc;
if (daemon->dumpfd == -1 || !(mask & daemon->dump_mask))
return;
/* So wireshark can Id the packet. */
udp.uh_sport = udp.uh_dport = htons(NAMESERVER_PORT);
#ifdef HAVE_IPV6
if (src)
family = src->sa.sa_family;
else
family = dst->sa.sa_family;
if (family == AF_INET6)
{
iphdr = &ip6;
ipsz = sizeof(ip6);
memset(&ip6, 0, sizeof(ip6));
ip6.ip6_vfc = 6 << 4;
ip6.ip6_plen = htons(sizeof(struct udphdr) + len);
ip6.ip6_nxt = IPPROTO_UDP;
ip6.ip6_hops = 64;
if (src)
{
memcpy(&ip6.ip6_src, &src->in6.sin6_addr, IN6ADDRSZ);
udp.uh_sport = src->in6.sin6_port;
}
if (dst)
{
memcpy(&ip6.ip6_dst, &dst->in6.sin6_addr, IN6ADDRSZ);
udp.uh_dport = dst->in6.sin6_port;
}
/* start UDP checksum */
for (sum = 0, i = 0; i < IN6ADDRSZ; i++)
sum += ((u16 *)&ip6.ip6_src)[i];
}
else
#endif
{
iphdr = &ip;
ipsz = sizeof(ip);
memset(&ip, 0, sizeof(ip));
ip.ip_v = IPVERSION;
ip.ip_hl = sizeof(struct ip) / 4;
ip.ip_len = htons(sizeof(struct ip) + sizeof(struct udphdr) + len);
ip.ip_ttl = IPDEFTTL;
ip.ip_p = IPPROTO_UDP;
if (src)
{
ip.ip_src = src->in.sin_addr;
udp.uh_sport = src->in.sin_port;
}
if (dst)
{
ip.ip_dst = dst->in.sin_addr;
udp.uh_dport = dst->in.sin_port;
}
ip.ip_sum = 0;
for (sum = 0, i = 0; i < sizeof(struct ip) / 2; i++)
sum += ((u16 *)&ip)[i];
while (sum >> 16)
sum = (sum & 0xffff) + (sum >> 16);
ip.ip_sum = (sum == 0xffff) ? sum : ~sum;
/* start UDP checksum */
sum = ip.ip_src.s_addr & 0xffff;
sum += (ip.ip_src.s_addr >> 16) & 0xffff;
sum += ip.ip_dst.s_addr & 0xffff;
sum += (ip.ip_dst.s_addr >> 16) & 0xffff;
}
if (len & 1)
((unsigned char *)packet)[len] = 0; /* for checksum, in case length is odd. */
udp.uh_sum = 0;
udp.uh_ulen = htons(sizeof(struct udphdr) + len);
sum += htons(IPPROTO_UDP);
sum += htons(sizeof(struct udphdr) + len);
for (i = 0; i < sizeof(struct udphdr)/2; i++)
sum += ((u16 *)&udp)[i];
for (i = 0; i < (len + 1) / 2; i++)
sum += ((u16 *)packet)[i];
while (sum >> 16)
sum = (sum & 0xffff) + (sum >> 16);
udp.uh_sum = (sum == 0xffff) ? sum : ~sum;
rc = gettimeofday(&time, NULL);
pcap_header.ts_sec = time.tv_sec;
pcap_header.ts_usec = time.tv_usec;
pcap_header.incl_len = pcap_header.orig_len = ipsz + sizeof(udp) + len;
if (rc == -1 ||
!read_write(daemon->dumpfd, (void *)&pcap_header, sizeof(pcap_header), 0) ||
!read_write(daemon->dumpfd, iphdr, ipsz, 0) ||
!read_write(daemon->dumpfd, (void *)&udp, sizeof(udp), 0) ||
!read_write(daemon->dumpfd, (void *)packet, len, 0))
my_syslog(LOG_ERR, _("failed to write packet dump"));
else
my_syslog(LOG_INFO, _("dumping UDP packet %u mask 0x%04x"), ++packet_count, mask);
}
#endif

37
src/forward.c
View File

@ -508,6 +508,10 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
if (errno == 0)
{
#ifdef HAVE_DUMPFILE
dump_packet(DUMP_UP_QUERY, (void *)header, plen, NULL, &start->addr);
#endif
/* Keep info in case we want to re-send this packet */
daemon->srv_save = start;
daemon->packet_len = plen;
@ -769,7 +773,7 @@ void reply_query(int fd, int family, time_t now)
#endif
header = (struct dns_header *)daemon->packet;
if (n < (int)sizeof(struct dns_header) || !(header->hb3 & HB3_QR))
return;
@ -796,6 +800,12 @@ void reply_query(int fd, int family, time_t now)
if (!(forward = lookup_frec(ntohs(header->id), hash)))
return;
#ifdef HAVE_DUMPFILE
dump_packet((forward->flags & (FREC_DNSKEY_QUERY | FREC_DS_QUERY)) ? DUMP_SEC_REPLY : DUMP_UP_REPLY,
(void *)header, n, &serveraddr, NULL);
#endif
/* log_query gets called indirectly all over the place, so
pass these in global variables - sorry. */
daemon->log_display_id = forward->log_id;
@ -934,6 +944,11 @@ void reply_query(int fd, int family, time_t now)
status = dnssec_validate_reply(now, header, n, daemon->namebuff, daemon->keyname, &forward->class,
!option_bool(OPT_DNSSEC_IGN_NS) && (server->flags & SERV_DO_DNSSEC),
NULL, NULL);
#ifdef HAVE_DUMPFILE
if (status == STAT_BOGUS)
dump_packet((forward->flags & (FREC_DNSKEY_QUERY | FREC_DS_QUERY)) ? DUMP_SEC_BOGUS : DUMP_BOGUS,
header, (size_t)n, &serveraddr, NULL);
#endif
}
/* Can't validate, as we're missing key data. Put this
@ -1060,6 +1075,11 @@ void reply_query(int fd, int family, time_t now)
setsockopt(fd, SOL_SOCKET, SO_MARK, &mark, sizeof(unsigned int));
}
#endif
#ifdef HAVE_DUMPFILE
dump_packet(DUMP_SEC_QUERY, (void *)header, (size_t)nn, NULL, &server->addr);
#endif
while (retry_send(sendto(fd, (char *)header, nn, 0,
&server->addr.sa,
sa_len(&server->addr))));
@ -1114,8 +1134,8 @@ void reply_query(int fd, int family, time_t now)
bogusanswer = 1;
}
}
#endif
#endif
/* restore CD bit to the value in the query */
if (forward->flags & FREC_CHECKING_DISABLED)
header->hb4 |= HB4_CD;
@ -1141,6 +1161,11 @@ void reply_query(int fd, int family, time_t now)
nn = resize_packet(header, nn, NULL, 0);
}
#endif
#ifdef HAVE_DUMPFILE
dump_packet(DUMP_REPLY, daemon->packet, (size_t)nn, NULL, &forward->source);
#endif
send_from(forward->fd, option_bool(OPT_NOWILD) || option_bool (OPT_CLEVERBIND), daemon->packet, nn,
&forward->source, &forward->dest, forward->iface);
}
@ -1394,7 +1419,11 @@ void receive_query(struct listener *listen, time_t now)
pass these in global variables - sorry. */
daemon->log_display_id = ++daemon->log_id;
daemon->log_source_addr = &source_addr;
#ifdef HAVE_DUMPFILE
dump_packet(DUMP_QUERY, daemon->packet, (size_t)n, &source_addr, NULL);
#endif
if (extract_request(header, (size_t)n, daemon->namebuff, &type))
{
#ifdef HAVE_AUTH

14
src/option.c
View File

@ -161,6 +161,8 @@ struct myoption {
#define LOPT_TFTP_MTU 349
#define LOPT_REPLY_DELAY 350
#define LOPT_RAPID_COMMIT 351
#define LOPT_DUMPFILE 352
#define LOPT_DUMPMASK 353
#ifdef HAVE_GETOPT_LONG
static const struct option opts[] =
@ -327,6 +329,8 @@ static const struct myoption opts[] =
{ "dhcp-ttl", 1, 0 , LOPT_DHCPTTL },
{ "dhcp-reply-delay", 1, 0, LOPT_REPLY_DELAY },
{ "dhcp-rapid-commit", 0, 0, LOPT_RAPID_COMMIT },
{ "dumpfile", 1, 0, LOPT_DUMPFILE },
{ "dumpmask", 1, 0, LOPT_DUMPMASK },
{ NULL, 0, 0, 0 }
};
@ -500,6 +504,8 @@ static struct {
{ LOPT_DHCPTTL, ARG_ONE, "<ttl>", gettext_noop("Set TTL in DNS responses with DHCP-derived addresses."), NULL },
{ LOPT_REPLY_DELAY, ARG_ONE, "<integer>", gettext_noop("Delay DHCP replies for at least number of seconds."), NULL },
{ LOPT_RAPID_COMMIT, OPT_RAPID_COMMIT, NULL, gettext_noop("Enables DHCPv4 Rapid Commit option."), NULL },
{ LOPT_DUMPFILE, ARG_ONE, "<path>", gettext_noop("Path to debug packet dump file"), NULL },
{ LOPT_DUMPMASK, ARG_ONE, "<hex>", gettext_noop("Mask which packets to dump"), NULL },
{ 0, 0, NULL, NULL, NULL }
};
@ -1811,6 +1817,14 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
ret_err(_("bad MX target"));
break;
case LOPT_DUMPFILE: /* --dumpfile */
daemon->dump_file = opt_string_alloc(arg);
break;
case LOPT_DUMPMASK: /* --dumpmask */
daemon->dump_mask = strtol(arg, NULL, 0);
break;
#ifdef HAVE_DHCP
case 'l': /* --dhcp-leasefile */
daemon->lease_file = opt_string_alloc(arg);