1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
|
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="Author" content="Mike Schiffman">
<meta name="GENERATOR" content="Mozilla/4.6 [en] (Win98; I) [Netscape]">
<title>Introduction</title>
</head>
<body text="#000000" bgcolor="#CCCCCC" link="#0000EE" vlink="#551A8B" alink="#FF0000">
<a href="7.html">Next</a> <a href="5.html">Previous</a> <a href="lrm.html">Top</a>
<br>
<hr ALIGN=LEFT WIDTH="97%">
<br><b><font size=+2>6. Sample applications</font></b>
<br>
<hr ALIGN=LEFT WIDTH="97%">
<br><font size=-1>The following are some simple examples that highlight
different areas of functionality offered by libnet. Each one of these
programs is autonomous and can be compiled into standalone executable.
We'll go through the first example step by step, to fully understand what's
going on, then, as we progress to subsequent examples, we will cover only
new or salient code. Comments are clearly visible in <font color="#FF0000">red</font><font color="#000000">.</font></font>
<p><font size=-1>To compile any of these examples (you can download the
C files from the corresponding links) simply:</font>
<p><tt><font size=-1>shattered:~> gcc -Wall `libnet-config --defines` libnet-example-x.c
-o libnet-example-x `libnet-config --libs`</font></tt>
<p>
<hr ALIGN=LEFT WIDTH="97%">
<br><a NAME="s6.1"></a><b><font size=+2>6.1 Example 1 [raw socket api -
TCP packet]</font></b>
<br><font size=-1>Download <a href="examples/libnet-example-1.c">libnet-example-1.c</a></font>
<p><tt><font size=-2>#include <libnet.h></font></tt>
<p><tt><font size=-2>void usage(char *);</font></tt>
<p><tt><font size=-2>int</font></tt>
<br><tt><font size=-2>main(int argc, char **argv)</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> int network,
/* our network interface */</font></tt>
<br><tt><font size=-2> packet_size,
/* packet size */</font></tt>
<br><tt><font size=-2> c;
/* misc */</font></tt>
<br><tt><font size=-2> u_long src_ip, dst_ip;
/* ip addresses */</font></tt>
<br><tt><font size=-2> u_short src_prt, dst_prt;
/* ports */</font></tt>
<br><tt><font size=-2> u_char *cp, *packet;
/* misc / packet */</font></tt>
<p><tt><font size=-2> printf("libnet example code:\tmodule
1\n\n");</font></tt>
<br><tt><font size=-2> printf("packet injection interface:\traw
socket\n");</font></tt>
<br><tt><font size=-2> printf("packet type:\t\t\tTCP
[no payload]\n");</font></tt>
<p><tt><font size=-2> src_ip = 0;</font></tt>
<br><tt><font size=-2> dst_ip = 0;</font></tt>
<br><tt><font size=-2> src_prt = 0;</font></tt>
<br><tt><font size=-2> dst_prt = 0;</font></tt>
<p><font color="#FF0000">Standard command line argument parsing.
We require a source IP and a destination IP, both in the form "ip.ip.ip.ip.port".</font>
<p><tt><font size=-2> while((c = getopt(argc, argv, "d:s:"))
!= EOF)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> switch
(c)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
/*</font></tt>
<br><tt><font size=-2>
* We expect the input to be of the form `ip.ip.ip.ip.port`.
We</font></tt>
<br><tt><font size=-2>
* point cp to the last dot of the IP address/port string and</font></tt>
<br><tt><font size=-2>
* then seperate them with a NULL byte. The optarg now points
to</font></tt>
<br><tt><font size=-2>
* just the IP address, and cp points to the port.</font></tt>
<br><tt><font size=-2>
*/</font></tt>
<br><tt><font size=-2>
case 'd':</font></tt>
<br><tt><font size=-2>
if (!(cp = strrchr(optarg, '.')))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
usage(argv[0]);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
*cp++ = 0;</font></tt>
<br><tt><font size=-2>
dst_prt = (u_short)atoi(cp);</font></tt>
<br><tt><font size=-2>
if (!(dst_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Bad destination IP address: %s\n", optarg);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 's':</font></tt>
<br><tt><font size=-2>
if (!(cp = strrchr(optarg, '.')))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
usage(argv[0]);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
*cp++ = 0;</font></tt>
<br><tt><font size=-2>
src_prt = (u_short)atoi(cp);</font></tt>
<br><tt><font size=-2>
if (!(src_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Bad source IP address: %s\n", optarg);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> if (!src_ip || !src_prt || !dst_ip
|| !dst_prt)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> usage(argv[0]);</font></tt>
<br><tt><font size=-2> exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">Our packet is a TCP/IP packet with no payload,
so we only need LIBNET_IP_H + LIBNET_TCP_H (40 bytes) of memory.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * We're just going
to build a TCP packet with no payload using the</font></tt>
<br><tt><font size=-2> * raw sockets API,
so we only need memory for a TCP header and an IP</font></tt>
<br><tt><font size=-2> * header.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> packet_size = LIBNET_IP_H + LIBNET_TCP_H;</font></tt>
<p><font color="#FF0000">We allocate the heap memory for our packet.
If it failed, this would be a fatal error that we couldn't recover from
so we would be done. When libnet_error is called with the LIBNET_ERR_FATAL
severity, the program exits. This is <i>only </i>defined exit point
inside of libnet.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 1: Memory initialization
(interchangable with step 2).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_init_packet(packet_size,
&packet);</font></tt>
<br><tt><font size=-2> if (packet == NULL)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_init_packet failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">Next we open up our network interface. Again
failure is fatal.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 2: Network
initialization (interchangable with step 1).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> network = libnet_open_raw_sock(IPPROTO_RAW);</font></tt>
<br><tt><font size=-2> if (network == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"Can't open network.\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">Now the fun begins. Like so many tinker
toys, or so much capsula, we build our packets. Note that no consideration
is given to data-types or byte-ordering (well almost no consideration for
data-types). This is all taken care of inside of libnet. All
you have to worry about is what values to stuff in there. Notice
that the order we call the modular packet constructors is unimportant.
The major thing to note is that we pass in the packet at the correct memory
location.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(IP header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_ip(LIBNET_TCP_H,
/* size of the packet sans IP header */</font></tt>
<br><tt><font size=-2>
IPTOS_LOWDELAY, /* IP tos
*/</font></tt>
<br><tt><font size=-2>
242,
/* IP ID */</font></tt>
<br><tt><font size=-2>
0,
/* frag stuff */</font></tt>
<br><tt><font size=-2>
48,
/* TTL */</font></tt>
<br><tt><font size=-2>
IPPROTO_TCP,
/* transport protocol */</font></tt>
<br><tt><font size=-2>
src_ip,
/* source IP */</font></tt>
<br><tt><font size=-2>
dst_ip,
/* destination IP */</font></tt>
<br><tt><font size=-2>
NULL,
/* payload (none) */</font></tt>
<br><tt><font size=-2>
0,
/* payload length */</font></tt>
<br><tt><font size=-2>
packet);
/* packet header memory */</font></tt>
<p><font color="#FF0000">Notice the TCP builder gets the packet memory
buffer at LIBNET_IP_H (20) bytes.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(TCP header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_tcp(src_prt,
/* source TCP port */</font></tt>
<br><tt><font size=-2>
dst_prt,
/* destination TCP port */</font></tt>
<br><tt><font size=-2>
0xa1d95,
/* sequence number */</font></tt>
<br><tt><font size=-2>
0x53,
/* acknowledgement number */</font></tt>
<br><tt><font size=-2>
TH_SYN,
/* control flags */</font></tt>
<br><tt><font size=-2>
1024,
/* window size */</font></tt>
<br><tt><font size=-2>
0,
/* urgent pointer */</font></tt>
<br><tt><font size=-2>
NULL,
/* payload (none) */</font></tt>
<br><tt><font size=-2>
0,
/* payload length */</font></tt>
<br><tt><font size=-2>
packet + LIBNET_IP_H); /* packet header memory */</font></tt>
<p><font color="#FF0000">Perform our checksum on the TCP header only.
Since we are using the raw sockets api, the kernel will handle our IP header
checksum for us. How thoughtful!</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 4: Packet checksums
(TCP header only).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_do_checksum(packet,
IPPROTO_TCP, LIBNET_TCP_H) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_do_checksum failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">In you go! The packet is sent on it's merry
little way!</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 5: Packet injection.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> c = libnet_write_ip(network, packet,
packet_size);</font></tt>
<br><tt><font size=-2> if (c < packet_size)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LN_ERR_WARNING,
"libnet_write_ip only wrote %d bytes\n", c);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> else</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> printf("construction
and injection completed, wrote all %d bytes\n", c);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">Since we're good programmers, we always shut things
down when we are done.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Shut down the interface.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_close_raw_sock(network)
== -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LN_ERR_WARNING,
"libnet_close_raw_sock couldn't close the interface");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Free packet memory.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_destroy_packet(&packet);</font></tt>
<p><tt><font size=-2> return (c == -1 ? EXIT_FAILURE
: EXIT_SUCCESS);</font></tt>
<br><tt><font size=-2>}</font></tt>
<br>
<p><tt><font size=-2>void</font></tt>
<br><tt><font size=-2>usage(char *name)</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> fprintf(stderr, "usage: %s -s
s_ip.s_port -d d_ip.d_port\n", name);</font></tt>
<br><tt><font size=-2>}</font></tt>
<br>
<p><tt><font size=-2>/* EOF */</font></tt>
<br>
<p>
<hr ALIGN=LEFT WIDTH="97%">
<p>
<hr ALIGN=LEFT WIDTH="97%">
<br><a NAME="s6.2"></a><b><font size=+2>6.2 Example 2 [link layer api -
ICMP_MASK]</font></b>
<br><font size=-1>Download <a href="examples/libnet-example-2.c">libnet-example-1.c</a></font>
<br>
<p><tt><font size=-2>#include <libnet.h></font></tt>
<p><tt><font size=-2>void usage(char *);</font></tt>
<p><tt><font size=-2>u_char enet_src[6] = {0x0d, 0x0e, 0x0a, 0x0d, 0x00,
0x00};</font></tt>
<br><tt><font size=-2>u_char enet_dst[6] = {0xff, 0xff, 0xff, 0xff, 0xff,
0xff};</font></tt>
<p><tt><font size=-2>int</font></tt>
<br><tt><font size=-2>main(int argc, char *argv[])</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> int packet_size,
/* size of our packet */</font></tt>
<br><tt><font size=-2> c;
/* misc */</font></tt>
<br><tt><font size=-2> u_long src_ip, dst_ip;
/* source ip, dest ip */</font></tt>
<br><tt><font size=-2> u_char *packet;
/* pointer to our packet buffer */</font></tt>
<br><tt><font size=-2> char err_buf[LIBNET_ERRBUF_SIZE];
/* error buffer */</font></tt>
<br><tt><font size=-2> u_char *device;
/* pointer to the device to use */</font></tt>
<br><tt><font size=-2> struct libnet_link_int *network;
/* pointer to link interface struct */</font></tt>
<p><tt><font size=-2> printf("libnet example code:\tmodule
2\n\n");</font></tt>
<br><tt><font size=-2> printf("packet injection interface:\tlink
layer\n");</font></tt>
<br><tt><font size=-2> printf("packet type:\t\t\tICMP
net mask [no payload]\n");</font></tt>
<p><tt><font size=-2> device = NULL;</font></tt>
<br><tt><font size=-2> src_ip = 0;</font></tt>
<br><tt><font size=-2> dst_ip = 0;</font></tt>
<p><font color="#FF0000">This time, we have an additional `device` to specify
the link layer device to use.</font>
<p><tt><font size=-2> while ((c = getopt(argc, argv,
"i:d:s:")) != EOF)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> switch
(c)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
case 'd':</font></tt>
<br><tt><font size=-2>
if (!(dst_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Bad destination IP address: %s\n", optarg);</font></tt>
<p><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 'i':</font></tt>
<br><tt><font size=-2>
device = optarg;</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 's':</font></tt>
<br><tt><font size=-2>
if (!(src_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Bad source IP address: %s\n", optarg);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
default:</font></tt>
<br><tt><font size=-2>
exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> if (!src_ip || !dst_ip)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> usage(argv[0]);</font></tt>
<br><tt><font size=-2> exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">If a device isn't specified, libnet will
attempt to choose one for you. libnet_select_device will return
the first `up` non-loopback device it finds.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 1: Network
Initialization (interchangable with step 2).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (device == NULL)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> struct
sockaddr_in sin;</font></tt>
<br><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2>
* Try to locate a device.</font></tt>
<br><tt><font size=-2>
*/</font></tt>
<br><tt><font size=-2> if (libnet_select_device(&sin,
&device, err_buf) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "libnet_select_device failed: %s\n", err_buf);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> printf("device:\t\t\t\t%s\n",
device);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">Instead of opening a raw socket, we're opening
up a link layer interface.</font>
<p><tt><font size=-2> if ((network = libnet_open_link_interface(device,
err_buf)) == NULL)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_open_link_interface: %s\n", err_buf);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">The ethernet header needs to be specified explicitly
in the packet size.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * We're going to build
an ICMP packet with no payload using the</font></tt>
<br><tt><font size=-2> * link-layer API,
so this time we need memory for a ethernet header</font></tt>
<br><tt><font size=-2> * as well as memory
for the ICMP and IP headers.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> packet_size = LIBNET_IP_H + LIBNET_ETH_H
+ LIBNET_ICMP_MASK_H;</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 2: Memory Initialization
(interchangable with step 1).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_init_packet(packet_size,
&packet) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_init_packet failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(ethernet header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_ethernet(enet_dst,</font></tt>
<br><tt><font size=-2>
enet_src,</font></tt>
<br><tt><font size=-2>
ETHERTYPE_IP,</font></tt>
<br><tt><font size=-2>
NULL,</font></tt>
<br><tt><font size=-2>
0,</font></tt>
<br><tt><font size=-2>
packet);</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(ICMP header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_icmp_mask(ICMP_MASKREPLY,
/* type */</font></tt>
<br><tt><font size=-2>
0,
/* code */</font></tt>
<br><tt><font size=-2>
242,
/* id */</font></tt>
<br><tt><font size=-2>
0,
/* seq */</font></tt>
<br><tt><font size=-2>
0xffffffff,
/* mask */</font></tt>
<br><tt><font size=-2>
NULL,
/* payload */</font></tt>
<br><tt><font size=-2>
0,
/* payload_s */</font></tt>
<br><tt><font size=-2>
packet + LIBNET_ETH_H + LIBNET_IP_H);</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(IP header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_ip(ICMP_MASK_H,</font></tt>
<br><tt><font size=-2>
0,
/* IP tos */</font></tt>
<br><tt><font size=-2>
242,
/* IP ID */</font></tt>
<br><tt><font size=-2>
0,
/* Frag */</font></tt>
<br><tt><font size=-2>
64,
/* TTL */</font></tt>
<br><tt><font size=-2>
IPPROTO_ICMP,
/* Transport protocol */</font></tt>
<br><tt><font size=-2>
src_ip,
/* Source IP */</font></tt>
<br><tt><font size=-2>
dst_ip,
/* Destination IP */</font></tt>
<br><tt><font size=-2>
NULL,
/* Pointer to payload (none) */</font></tt>
<br><tt><font size=-2>
0,</font></tt>
<br><tt><font size=-2>
packet + LIBNET_ETH_H); /* Packet header memory */</font></tt>
<p><font color="#FF0000">The IP header checksum must be explicitly computed
for the link layer interface.</font>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 4: Packet checksums
(ICMP header *AND* IP header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_do_checksum(packet
+ ETH_H, IPPROTO_ICMP, LIBNET_ICMP_MASK_H) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_do_checksum failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> if (libnet_do_checksum(packet
+ ETH_H, IPPROTO_IP, LIBNET_IP_H) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_do_checksum failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 5: Packet injection.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> c = libnet_write_link_layer(network,
device, packet, packet_size);</font></tt>
<br><tt><font size=-2> if (c < packet_size)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LN_ERR_WARNING,
"libnet_write_link_layer only wrote %d bytes\n", c);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> else</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> printf("construction
and injection completed, wrote all %d bytes\n", c);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Shut down the interface.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_close_link_interface(network)
== -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LN_ERR_WARNING,
"libnet_close_link_interface couldn't close the interface");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Free packet memory.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_destroy_packet(&packet);</font></tt>
<p><tt><font size=-2> return (c == -1 ? EXIT_FAILURE
: EXIT_SUCCESS);</font></tt>
<br><tt><font size=-2>}</font></tt>
<br>
<p><tt><font size=-2>void</font></tt>
<br><tt><font size=-2>usage(char *name)</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> fprintf(stderr, "usage: %s [-i
interface] -s s_ip -d d_ip\n", name);</font></tt>
<br><tt><font size=-2>}</font></tt>
<p><tt><font size=-2>/* EOF */</font></tt>
<p>
<hr ALIGN=LEFT WIDTH="97%">
<p>
<hr ALIGN=LEFT WIDTH="97%">
<br><a NAME="s6.3"></a><b><font size=+2>6.3 Example 3 [raw socket api -
ICMP_ECHO using an arena]</font></b>
<br><font size=-1>Download <a href="examples/libnet-example-3.c">libnet-example-1.c</a></font>
<p><tt><font size=-2>#include <libnet.h></font></tt>
<p><tt><font size=-2>void usage(char *);</font></tt>
<br>
<p><tt><font size=-2>int</font></tt>
<br><tt><font size=-2>main(int argc, char **argv)</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> int network, n, c, number_of_packets,
packet_size;</font></tt>
<br><tt><font size=-2> struct libnet_arena arena, *arena_p;</font></tt>
<br><tt><font size=-2> u_char *packets[10];</font></tt>
<br><tt><font size=-2> u_long src_ip, dst_ip;</font></tt>
<p><tt><font size=-2> printf("libnet example code:\tmodule
3\n\n");</font></tt>
<br><tt><font size=-2> printf("packet injection interface:\tlink
layer\n");</font></tt>
<br><tt><font size=-2> printf("packet type:\t\t\tICMP_ECHO
[no payload] using an arena\n");</font></tt>
<p><tt><font size=-2> src_ip = 0;</font></tt>
<br><tt><font size=-2> dst_ip = 0;</font></tt>
<br><tt><font size=-2> while((c = getopt(argc, argv,
"d:s:")) != EOF)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> switch
(c)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
case 'd':</font></tt>
<br><tt><font size=-2>
if (!(dst_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Bad destination IP address: %s\n", optarg);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 's':</font></tt>
<br><tt><font size=-2>
if (!(src_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Bad source IP address: %s\n", optarg);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> if (!src_ip || !dst_ip)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> usage(argv[0]);</font></tt>
<br><tt><font size=-2> exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * We're just going
to build an ICMP packet with no payload using the</font></tt>
<br><tt><font size=-2> * raw sockets API,
so we only need memory for a ICMP header and an IP</font></tt>
<br><tt><font size=-2> * header.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> packet_size = LIBNET_IP_H + LIBNET_ICMP_ECHO_H;</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Let's just build
say, 10 packets.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> number_of_packets = 10;</font></tt>
<p><font color="#FF0000">The arena can be thought of as a pool of memory
that can be called upon to yield usable memory until it dries up.
In this case, we'll have enough memory for 10 packets of the above packet
size.</font>
<p><tt><font size=-2> arena_p = &arena;</font></tt>
<br><tt><font size=-2> if (libnet_init_packet_arena(&arena_p,
number_of_packets, packet_size) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_init_packet_arena failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> else</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> printf("Allocated
an arena of %ld bytes..\n", LIBNET_GET_ARENA_SIZE(arena));</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> network = libnet_open_raw_sock(IPPROTO_RAW);</font></tt>
<br><tt><font size=-2> if (network == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"Can't open the network.\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">We'll keep grabbing chunks of memory from the
arena to build packets until it runs dry. This isn't the most useful
implementation of an arena as all of the packets are the same (a for loop
around in the injection call would accomplish the same thing without an
arena). Arenas really become useful when you're injecting packets
of different types (the arena is used to preload packets).</font>
<p><tt><font size=-2> for (n = 0; n < number_of_packets;
n++)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> printf("%ld
bytes remaining in arena\n", LIBNET_GET_ARENA_REMAINING_BYTES(arena));</font></tt>
<br><tt><font size=-2> packets[n]
= libnet_next_packet_from_arena(&arena_p, packet_size);</font></tt>
<br><tt><font size=-2> if (!packets[n])</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_WARNING, "Arena is empty\n");</font></tt>
<br><tt><font size=-2>
continue;</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> libnet_build_ip(ICMP_ECHO_H,
/* Size of the payload */</font></tt>
<br><tt><font size=-2>
IPTOS_LOWDELAY | IPTOS_THROUGHPUT, /* IP tos */</font></tt>
<br><tt><font size=-2>
242,
/* IP ID */</font></tt>
<br><tt><font size=-2>
0,
/* frag stuff */</font></tt>
<br><tt><font size=-2>
48,
/* TTL */</font></tt>
<br><tt><font size=-2>
IPPROTO_ICMP,
/* transport protocol */</font></tt>
<br><tt><font size=-2>
src_ip,
/* source IP */</font></tt>
<br><tt><font size=-2>
dst_ip,
/* destination IP */</font></tt>
<br><tt><font size=-2>
NULL,
/* pointer to payload */</font></tt>
<br><tt><font size=-2>
0,
/* payload length */</font></tt>
<br><tt><font size=-2>
packets[n]);
/* packet header memory */</font></tt>
<p><tt><font size=-2> libnet_build_icmp_echo(ICMP_ECHO,
/* type */</font></tt>
<br><tt><font size=-2>
0,
/* code */</font></tt>
<br><tt><font size=-2>
242,
/* id */</font></tt>
<br><tt><font size=-2>
5,
/* seq */</font></tt>
<br><tt><font size=-2>
NULL,
/* pointer to payload */</font></tt>
<br><tt><font size=-2>
0,
/* payload length */</font></tt>
<br><tt><font size=-2>
packets[n] + LIBNET_IP_H);
/* packet header memory */</font></tt>
<p><tt><font size=-2> if (libnet_do_checksum(packets[n],
IPPROTO_ICMP, LIBNET_ICMP_ECHO_H) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "libnet_do_checksum failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> c = libnet_write_ip(network,
packets[n], packet_size);</font></tt>
<br><tt><font size=-2> if (c
< packet_size)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
libnet_error(LN_ERR_WARNING, "libnet_write_ip only wrote %d bytes\n", c);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> else</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
printf("construction and injection of packet %d of %d completed, wrote
all %d bytes\n", n + 1, number_of_packets, c);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> libnet_destroy_packet_arena(&arena_p);</font></tt>
<br><tt><font size=-2> return (c == -1 ? EXIT_FAILURE
: EXIT_SUCCESS);</font></tt>
<br><tt><font size=-2>}</font></tt>
<br>
<p><tt><font size=-2>void</font></tt>
<br><tt><font size=-2>usage(char *name)</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> fprintf(stderr, "usage: %s -s
source_ip -d destination_ip\n ", name);</font></tt>
<br><tt><font size=-2>}</font></tt>
<p><tt><font size=-2>/* EOF */</font></tt>
<p>
<hr ALIGN=LEFT WIDTH="97%">
<p>
<hr ALIGN=LEFT WIDTH="97%">
<br><a NAME="s6.4"></a><b><font size=+2>6.4 Example 4 [link-layer api -
UDP packet using port list chaining]</font></b>
<br><font size=-1>Download <a href="examples/libnet-example-4.c">libnet-example-1.c</a></font>
<p><tt><font size=-2>#include <libnet.h></font></tt>
<p><tt><font size=-2>#define MAX_PAYLOAD_SIZE 1024</font></tt>
<p><tt><font size=-2>void usage(char *);</font></tt>
<p><tt><font size=-2>u_char enet_src[6] = {0x0d, 0x0e, 0x0a, 0x0d, 0x00,
0x00};</font></tt>
<br><tt><font size=-2>u_char enet_dst[6] = {0xff, 0xff, 0xff, 0xff, 0xff,
0xff};</font></tt>
<p><tt><font size=-2>int</font></tt>
<br><tt><font size=-2>main(int argc, char *argv[])</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> int packet_size,
/* size of our packet */</font></tt>
<br><tt><font size=-2> payload_size,
/* size of our packet */</font></tt>
<br><tt><font size=-2> c;
/* misc */</font></tt>
<br><tt><font size=-2> u_long src_ip, dst_ip;
/* source ip, dest ip */</font></tt>
<br><tt><font size=-2> u_short bport, eport;
/* beginning and end ports */</font></tt>
<br><tt><font size=-2> u_short cport;
/* current port */</font></tt>
<br><tt><font size=-2> u_char payload[MAX_PAYLOAD_SIZE];
/* packet payload */</font></tt>
<br><tt><font size=-2> u_char *packet;
/* pointer to our packet buffer */</font></tt>
<br><tt><font size=-2> char err_buf[LIBNET_ERRBUF_SIZE];
/* error buffer */</font></tt>
<br><tt><font size=-2> u_char *device;
/* pointer to the device to use */</font></tt>
<br><tt><font size=-2> struct libnet_link_int *network;
/* pointer to link interface struct */</font></tt>
<br><tt><font size=-2> struct libnet_plist_chain plist;
/* plist chain */</font></tt>
<br><tt><font size=-2> struct libnet_plist_chain *plist_p;
/* plist chain pointer */</font></tt>
<p><tt><font size=-2> printf("libnet example code:\tmodule
4\n\n");</font></tt>
<br><tt><font size=-2> printf("packet injection interface:\tlink
layer\n");</font></tt>
<br><tt><font size=-2> printf("packet type:\t\t\tUDP
[with payload] using port list chaining\n");</font></tt>
<p><tt><font size=-2> plist_p = NULL;</font></tt>
<br><tt><font size=-2> device = NULL;</font></tt>
<br><tt><font size=-2> src_ip = 0;</font></tt>
<br><tt><font size=-2> dst_ip = 0;</font></tt>
<p><font color="#FF0000">HEY LOOK! We have another argument for the
port list. Port lists must be specified as ranges delimited by dashes,
with multiple ranges delimited by commas. See <a href="5.html#s5.5">section
5</a> (support functions) for more information on port list chain syntax.</font>
<p><tt><font size=-2> while ((c = getopt(argc, argv,
"i:d:s:p:")) != EOF)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> switch
(c)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
case 'd':</font></tt>
<br><tt><font size=-2>
if (!(dst_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL,</font></tt>
<br><tt><font size=-2>
"Bad destination IP address: %s\n", optarg);</font></tt>
<p><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 'i':</font></tt>
<br><tt><font size=-2>
device = optarg;</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 's':</font></tt>
<br><tt><font size=-2>
if (!(src_ip = libnet_name_resolve(optarg, LIBNET_RESOLVE)))</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL,</font></tt>
<br><tt><font size=-2>
"Bad source IP address: %s\n", optarg);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
case 'p':</font></tt>
<br><tt><font size=-2>
plist_p = &plist;</font></tt>
<br><tt><font size=-2>
if (libnet_plist_chain_new(&plist_p, optarg) == -1)</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "Could not build port list\n");</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
break;</font></tt>
<br><tt><font size=-2>
default:</font></tt>
<br><tt><font size=-2>
usage(argv[0]);</font></tt>
<br><tt><font size=-2>
exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> if (!src_ip || !dst_ip || !plist_p)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> usage(argv[0]);</font></tt>
<br><tt><font size=-2> exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><font color="#FF0000">We also require an argument for the packet payload.
This code is probably not proof from overflows so take heed.</font><font color="#FF0000"></font>
<p><tt><font size=-2> c = argc - optind;</font></tt>
<br><tt><font size=-2> if (c != 1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> usage(argv[0]);</font></tt>
<br><tt><font size=-2> exit(EXIT_FAILURE);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> memset(payload, 0, sizeof(payload));</font></tt>
<br><tt><font size=-2> strncpy(payload, argv[optind],
strlen(argv[optind]));</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 1: Network
Initialization (interchangable with step 2).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (device == NULL)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> struct
sockaddr_in sin;</font></tt>
<br><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2>
* Try to locate a device.</font></tt>
<br><tt><font size=-2>
*/</font></tt>
<br><tt><font size=-2> if (libnet_select_device(&sin,
&device, err_buf) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "libnet_select_device failed: %s\n", err_buf);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> printf("device:\t\t\t\t%s\n",
device);</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> if ((network = libnet_open_link_interface(device,
err_buf)) == NULL)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_open_link_interface: %s\n", err_buf);</font></tt>
<br><tt><font size=-2> }</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Get the payload
from the user. Hrm. This might fail on a Sparc</font></tt>
<br><tt><font size=-2> * if byte alignment
is off...</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> payload_size = strlen(payload);</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * We're going to build
a UDP packet with a payload using the</font></tt>
<br><tt><font size=-2> * link-layer API,
so this time we need memory for a ethernet header</font></tt>
<br><tt><font size=-2> * as well as memory
for the ICMP and IP headers and our payload.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> packet_size = LIBNET_IP_H + LIBNET_ETH_H
+ LIBNET_UDP_H + payload_size;</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 2: Memory Initialization
(interchangable with step 1).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_init_packet(packet_size,
&packet) == -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LIBNET_ERR_FATAL,
"libnet_init_packet failed\n");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(ethernet header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_ethernet(enet_dst,</font></tt>
<br><tt><font size=-2>
enet_src,</font></tt>
<br><tt><font size=-2>
ETHERTYPE_IP,</font></tt>
<br><tt><font size=-2>
NULL,</font></tt>
<br><tt><font size=-2>
0,</font></tt>
<br><tt><font size=-2>
packet);</font></tt>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Step 3: Packet construction
(IP header).</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_build_ip(LIBNET_UDP_H +
payload_size,</font></tt>
<br><tt><font size=-2>
0,
/* IP tos */</font></tt>
<br><tt><font size=-2>
242,
/* IP ID */</font></tt>
<br><tt><font size=-2>
0,
/* Frag */</font></tt>
<br><tt><font size=-2>
64,
/* TTL */</font></tt>
<br><tt><font size=-2>
IPPROTO_UDP,
/* Transport protocol */</font></tt>
<br><tt><font size=-2>
src_ip,
/* Source IP */</font></tt>
<br><tt><font size=-2>
dst_ip,
/* Destination IP */</font></tt>
<br><tt><font size=-2>
NULL,
/* Pointer to payload (none) */</font></tt>
<br><tt><font size=-2>
0,</font></tt>
<br><tt><font size=-2>
packet + LIBNET_ETH_H); /* Packet header memory */</font></tt>
<p><font color="#FF0000">We run in a loop, grabbing port list ranges as
we go. We only really need to update the UDP port and checksum portions
of the packet, but for simplicity's sake, we'll lump it all together thusly...</font><font color="#FF0000"></font>
<p><tt><font size=-2> while (libnet_plist_chain_next_pair(plist_p,
&bport, &eport))</font></tt>
<br><tt><font size=-2> {</font></tt><font color="#FF0000"></font>
<p><font color="#FF0000">Check to see if we've exhausted our cache of port
list ranges.</font><font color="#FF0000"></font>
<p><tt><font size=-2> while (!(bport
> eport) && bport != 0)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2>
cport = bport++;</font></tt>
<br><tt><font size=-2>
/*</font></tt>
<br><tt><font size=-2>
* Step 3: Packet construction (UDP header).</font></tt>
<br><tt><font size=-2>
*/</font></tt>
<br><tt><font size=-2>
libnet_build_udp(242,
/* source port */</font></tt>
<br><tt><font size=-2>
cport,
/* dest. port */</font></tt>
<br><tt><font size=-2>
payload,
/* payload */</font></tt>
<br><tt><font size=-2>
payload_size,
/* payload length */</font></tt>
<br><tt><font size=-2>
packet + LIBNET_ETH_H + LIBNET_IP_H);</font></tt>
<p><tt><font size=-2>
/*</font></tt>
<br><tt><font size=-2>
* Step 4: Packet checksums (ICMP header *AND* IP header).</font></tt>
<br><tt><font size=-2>
*/</font></tt>
<br><tt><font size=-2>
if (libnet_do_checksum(packet + ETH_H, IPPROTO_UDP, LIBNET_UDP_H + payload_size)
== -1)</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "libnet_do_checksum failed\n");</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
if (libnet_do_checksum(packet + ETH_H, IPPROTO_IP, LIBNET_IP_H) == -1)</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LIBNET_ERR_FATAL, "libnet_do_checksum failed\n");</font></tt>
<br><tt><font size=-2>
}</font></tt>
<p><tt><font size=-2>
/*</font></tt>
<br><tt><font size=-2>
* Step 5: Packet injection.</font></tt>
<br><tt><font size=-2>
*/</font></tt>
<br><tt><font size=-2>
c = libnet_write_link_layer(network, device, packet, packet_size);</font></tt>
<br><tt><font size=-2>
if (c < packet_size)</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
libnet_error(LN_ERR_WARNING, "libnet_write_link_layer only wrote %d bytes\n",
c);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2>
else</font></tt>
<br><tt><font size=-2>
{</font></tt>
<br><tt><font size=-2>
printf("construction and injection completed, wrote all %d bytes, port
%d\n", c, cport);</font></tt>
<br><tt><font size=-2>
}</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> }</font></tt>
<br><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Shut down the interface.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> if (libnet_close_link_interface(network)
== -1)</font></tt>
<br><tt><font size=-2> {</font></tt>
<br><tt><font size=-2> libnet_error(LN_ERR_WARNING,
"libnet_close_link_interface couldn't close the interface");</font></tt>
<br><tt><font size=-2> }</font></tt>
<br>
<p><tt><font size=-2> /*</font></tt>
<br><tt><font size=-2> * Free packet memory.</font></tt>
<br><tt><font size=-2> */</font></tt>
<br><tt><font size=-2> libnet_destroy_packet(&packet);</font></tt>
<p><tt><font size=-2> return (c == -1 ? EXIT_FAILURE
: EXIT_SUCCESS);</font></tt>
<br><tt><font size=-2>}</font></tt>
<br>
<p><tt><font size=-2>void</font></tt>
<br><tt><font size=-2>usage(char *name)</font></tt>
<br><tt><font size=-2>{</font></tt>
<br><tt><font size=-2> fprintf(stderr, "usage: %s [-i
interface] -s s_ip -d d_ip -p port list payload\n", name);</font></tt>
<br><tt><font size=-2>}</font></tt>
<p><tt><font size=-2>/* EOF */</font></tt>
<p>
<hr ALIGN=LEFT WIDTH="97%">
<p>
<hr ALIGN=LEFT WIDTH="97%">
<p><a href="7.html">Next</a> <a href="5.html">Previous</a> <a href="lrm.html">Top</a>
</body>
</html>
|
