1 /*
2  * Radio tap as exported by BSD and Linux.
3  * The wireless ethernet devices return this format on Linux
4  * when running in monitor mode.
5  *
6  * TODO: Automatically determine whether the ethernet
7  * device is radio or ether, so that -h is not needed.
8  */
9 
10 #include <u.h>
11 #include <libc.h>
12 #include <ip.h>
13 #include "dat.h"
14 #include "protos.h"
15 
16 static Mux p_mux[] =
17 {
18 	{ "802.11", 0 },
19 	{ 0 }
20 };
21 
22 typedef struct Hdr Hdr;
23 struct Hdr
24 {
25 	uchar vers;
26 	uchar pad;
27 	ushort	len;
28 	ulong	present;
29 };
30 
31 static int
32 unpackhdr(uchar *p, uchar *ep, Hdr *h)
33 {
34 	if(p+sizeof(Hdr) > ep)
35 		return -1;
36 	h->vers = p[0];
37 	h->pad = p[1];
38 	h->len = LittleS(p+2);
39 	h->present = LittleL(p+4);
40 	// can be more present fields if 0x80000000 is set in each along the chain.
41 	if(p+h->len > ep)
42 		return -1;
43 	return 0;
44 }
45 
46 enum
47 {
48 	Ot,
49 };
50 
51 static Field p_fields[] =
52 {
53 	{ 0 }
54 };
55 
56 static void
57 p_compile(Filter *f)
58 {
59 	Mux *m;
60 
61 	if(f->op == '='){
62 		compile_cmp(radiotap.name, f, p_fields);
63 		return;
64 	}
65 	for(m = p_mux; m->name != nil; m++){
66 		if(strcmp(f->s, m->name) == 0){
67 			f->pr = m->pr;
68 			f->ulv = m->val;
69 			f->subop = Ot;
70 			return;
71 		}
72 	}
73 	sysfatal("unknown radiotap field or protocol: %s", f->s);
74 }
75 
76 static int
77 p_filter(Filter *f, Msg *m)
78 {
79 	Hdr h;
80 
81 	memset(&h, 0, sizeof h);
82 	if(unpackhdr(m->ps, m->pe, &h) < 0)
83 		return 0;
84 	m->ps += h.len;
85 	switch(f->subop){
86 	case Ot:
87 		return 1;
88 	}
89 	return 0;
90 }
91 
92 static int
93 p_seprint(Msg *m)
94 {
95 	Hdr h;
96 
97 	memset(&h, 0, sizeof h);
98 	if(unpackhdr(m->ps, m->pe, &h) < 0)
99 		return -1;
100 
101 	m->p = seprint(m->p, m->e, "%.*H", h.len, m->ps);
102 	m->ps += h.len;
103 	m->pr = &p80211;
104 	return 0;
105 }
106 
107 Proto radiotap =
108 {
109 	"radiotap",
110 	p_compile,
111 	p_filter,
112 	p_seprint,
113 	p_mux,
114 	nil,
115 	nil,
116 	defaultframer
117 };