1 /*
2 * getif.c : get an interface structure
3 *
4 * $FreeBSD: src/libexec/bootpd/getif.c,v 1.7 1999/08/28 00:09:18 peter Exp $
5 */
6
7 #include <sys/types.h>
8 #include <sys/socket.h>
9 #include <sys/ioctl.h>
10
11 #if defined(SUNOS) || defined(SVR4)
12 #include <sys/sockio.h>
13 #endif
14 #ifdef SVR4
15 #include <sys/stropts.h>
16 #endif
17
18 #include <sys/time.h> /* for struct timeval in net/if.h */
19 #include <net/if.h> /* for struct ifreq */
20 #include <netinet/in.h>
21
22 #ifndef NO_UNISTD
23 #include <unistd.h>
24 #endif
25 #include <syslog.h>
26 #include <errno.h>
27 #include <assert.h>
28
29 #include "getif.h"
30 #include "report.h"
31
32 #ifdef __bsdi__
33 #define BSD 43
34 #endif
35
36 static struct ifreq ifreq[10]; /* Holds interface configuration */
37 static struct ifconf ifconf; /* points to ifreq */
38
39 static int nmatch();
40
41 /*
42 * Return a pointer to the interface struct for the passed address.
43 *
44 * s socket file descriptor
45 * addrp destination address on interface
46 */
47 struct ifreq *
getif(int s,struct in_addr * addrp)48 getif(int s, struct in_addr *addrp)
49 {
50 int maxmatch;
51 int len, m, incr;
52 struct ifreq *ifrq, *ifrmax;
53 struct sockaddr_in *sip;
54 char *p;
55
56 /* If no address was supplied, just return NULL. */
57 if (!addrp)
58 return NULL;
59
60 /* Get the interface config if not done already. */
61 if (ifconf.ifc_len == 0) {
62 #ifdef SVR4
63 /*
64 * SysVr4 returns garbage if you do this the obvious way!
65 * This one took a while to figure out... -gwr
66 */
67 struct strioctl ioc;
68 ioc.ic_cmd = SIOCGIFCONF;
69 ioc.ic_timout = 0;
70 ioc.ic_len = sizeof(ifreq);
71 ioc.ic_dp = (char *) ifreq;
72 m = ioctl(s, I_STR, (char *) &ioc);
73 ifconf.ifc_len = ioc.ic_len;
74 ifconf.ifc_req = ifreq;
75 #else /* SVR4 */
76 ifconf.ifc_len = sizeof(ifreq);
77 ifconf.ifc_req = ifreq;
78 m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
79 #endif /* SVR4 */
80 if ((m < 0) || (ifconf.ifc_len <= 0)) {
81 report(LOG_ERR, "ioctl SIOCGIFCONF");
82 return NULL;
83 }
84 }
85 maxmatch = 7; /* this many bits or less... */
86 ifrmax = NULL; /* ... is not a valid match */
87 p = (char *) ifreq;
88 len = ifconf.ifc_len;
89 while (len > 0) {
90 ifrq = (struct ifreq *) p;
91 sip = (struct sockaddr_in *) &ifrq->ifr_addr;
92 m = nmatch(addrp, &(sip->sin_addr));
93 if (m > maxmatch) {
94 maxmatch = m;
95 ifrmax = ifrq;
96 }
97 #ifndef IFNAMSIZ
98 /* BSD not defined or earlier than 4.3 */
99 incr = sizeof(*ifrq);
100 #else
101 incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
102 #endif
103
104 p += incr;
105 len -= incr;
106 }
107
108 return ifrmax;
109 }
110
111 /*
112 * Return the number of leading bits matching in the
113 * internet addresses supplied.
114 *
115 * ca, cb ptrs to IP address, network order
116 */
117 static int
nmatch(u_char * ca,u_char * cb)118 nmatch(u_char *ca, u_char *cb)
119 {
120 u_int m = 0; /* count of matching bits */
121 u_int n = 4; /* bytes left, then bitmask */
122
123 /* Count matching bytes. */
124 while (n && (*ca == *cb)) {
125 ca++;
126 cb++;
127 m += 8;
128 n--;
129 }
130 /* Now count matching bits. */
131 if (n) {
132 n = 0x80;
133 while (n && ((*ca & n) == (*cb & n))) {
134 m++;
135 n >>= 1;
136 }
137 }
138 return (m);
139 }
140