1 /*
2 * getif.c : get an interface structure
3 */
4
5 #include <sys/types.h>
6 #include <sys/socket.h>
7 #include <sys/ioctl.h>
8
9 #if defined(SUNOS) || defined(SVR4)
10 #include <sys/sockio.h>
11 #endif
12 #ifdef SVR4
13 #include <sys/stropts.h>
14 #endif
15
16 #include <sys/time.h> /* for struct timeval in net/if.h */
17 #include <net/if.h> /* for struct ifreq */
18 #include <netinet/in.h>
19
20 #ifndef NO_UNISTD
21 #include <unistd.h>
22 #endif
23 #include <syslog.h>
24 #include <errno.h>
25 #include <assert.h>
26
27 #include "getif.h"
28 #include "report.h"
29
30 #ifdef __bsdi__
31 #define BSD 43
32 #endif
33
34 static struct ifreq ifreq[10]; /* Holds interface configuration */
35 static struct ifconf ifconf; /* points to ifreq */
36
37 static int nmatch(u_char *ca, u_char *cb);
38
39 /* Return a pointer to the interface struct for the passed address. */
40 struct ifreq *
getif(int s,struct in_addr * addrp)41 getif(int s, struct in_addr *addrp)
42 {
43 int maxmatch;
44 int len, m, incr;
45 struct ifreq *ifrq, *ifrmax;
46 struct sockaddr_in *sip;
47 char *p;
48
49 /* If no address was supplied, just return NULL. */
50 if (!addrp)
51 return (struct ifreq *) 0;
52
53 /* Get the interface config if not done already. */
54 if (ifconf.ifc_len == 0) {
55 #ifdef SVR4
56 /*
57 * SysVr4 returns garbage if you do this the obvious way!
58 * This one took a while to figure out... -gwr
59 */
60 struct strioctl ioc;
61 ioc.ic_cmd = SIOCGIFCONF;
62 ioc.ic_timout = 0;
63 ioc.ic_len = sizeof(ifreq);
64 ioc.ic_dp = (char *) ifreq;
65 m = ioctl(s, I_STR, (char *) &ioc);
66 ifconf.ifc_len = ioc.ic_len;
67 ifconf.ifc_req = ifreq;
68 #else /* SVR4 */
69 ifconf.ifc_len = sizeof(ifreq);
70 ifconf.ifc_req = ifreq;
71 m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
72 #endif /* SVR4 */
73 if ((m < 0) || (ifconf.ifc_len <= 0)) {
74 report(LOG_ERR, "ioctl SIOCGIFCONF");
75 return (struct ifreq *) 0;
76 }
77 }
78 maxmatch = 7; /* this many bits or less... */
79 ifrmax = (struct ifreq *) 0;/* ... is not a valid match */
80 p = (char *) ifreq;
81 len = ifconf.ifc_len;
82 while (len > 0) {
83 ifrq = (struct ifreq *) p;
84 sip = (struct sockaddr_in *) &ifrq->ifr_addr;
85 m = nmatch((u_char *)addrp, (u_char *)&(sip->sin_addr));
86 if (m > maxmatch) {
87 maxmatch = m;
88 ifrmax = ifrq;
89 }
90 #ifndef IFNAMSIZ
91 /* BSD not defined or earlier than 4.3 */
92 incr = sizeof(*ifrq);
93 #else
94 incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
95 #endif
96
97 p += incr;
98 len -= incr;
99 }
100
101 return ifrmax;
102 }
103
104 /*
105 * Return the number of leading bits matching in the
106 * internet addresses supplied.
107 */
108 static int
nmatch(u_char * ca,u_char * cb)109 nmatch(u_char *ca, u_char *cb)
110 {
111 u_int m = 0; /* count of matching bits */
112 u_int n = 4; /* bytes left, then bitmask */
113
114 /* Count matching bytes. */
115 while (n && (*ca == *cb)) {
116 ca++;
117 cb++;
118 m += 8;
119 n--;
120 }
121 /* Now count matching bits. */
122 if (n) {
123 n = 0x80;
124 while (n && ((*ca & n) == (*cb & n))) {
125 m++;
126 n >>= 1;
127 }
128 }
129 return (m);
130 }
131
132 /*
133 * Local Variables:
134 * tab-width: 4
135 * c-indent-level: 4
136 * c-argdecl-indent: 4
137 * c-continued-statement-offset: 4
138 * c-continued-brace-offset: -4
139 * c-label-offset: -4
140 * c-brace-offset: 0
141 * End:
142 */
143