summaryrefslogtreecommitdiffstats
path: root/localuser.c
blob: f8265e91898334e596ff1af690e9f2186fa69c84 (plain)
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
/*
 * Copyright 2018 IoT.bzh <jose.bollo@iot.bzh>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
/*
 * localuser.c
 * -----------
 *  This source file provides NSS (Name Service Switch -see [1]-) facilities
 *  for defining a virtual host of name localuser that resolves to an address
 *  of the localhost that integrate user ID.
 *
 *  The name "localuser" is resolved to the IPv4 address 127.x.y.z
 *  where x.y.z resolves to the current user UID = 65536*(x - 128) + 256*y + z
 *
 *  The name "localuser-UID" is resolved to the address 127.x.y.z
 *  where UID = 65536*(x - 128) + 256*y + z
 *
 *  Allowed UID are from 0 to 4194303 included.
 *
 *  Examples:
 *    localuser      => 127.128.0.0   (when UID = 0)
 *    localuser      => 127.128.3.233 (when UID = 1001)
 *    localuser-1024 => 127.128.4.0   (always)
 *
 *  This module provides the reverse resolution.
 *
 *  This module provides a value for IPv6: it translate to a IPv4-mapped IPv6 address
 *  because IPv6 lakes of loopback range.
 *
 *  Example: localuser-1024 => ::ffff:127.128.4.0
 *
 * links
 * -----
 *  [1] https://www.gnu.org/software/libc/manual/html_node/Name-Service-Switch.html
 */
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>
#include <nss.h>

/* string for "localuser" */
static const char localuser[] = "localuser";
static const char separator = '-';

/* defines the length of adresses */
static const int lenip4 = 4;
static const int lenip6 = 16;

/* masks for IPv4 adresses */
static const uint32_t prefix_mask  = 0xffc00000u; /* 255.192.0.0 */
static const uint32_t prefix_value = 0x7f800000u; /* 127.128.0.0 */
static const uint32_t locusr_mask  = 0x003fffffu; /* 0.63.255.255 */

/* return the IPv4 localuser address for 'uid' */
static uint32_t get_localuser(uint32_t uid)
{
	uint32_t adr = (uint32_t)(prefix_value | (locusr_mask & uid));
	return htonl(adr);
}

/* is 'ip' a localuser IPv4 address ? */
static int is_localuser(uint32_t ip)
{
	return prefix_value == (ntohl(ip) & prefix_mask);
}

/* return the user of the localuser IPv4 'ip' */
static uint32_t uid_of_localuser(uint32_t ip)
{
	return (ntohl(ip) & locusr_mask);
}

/* put in 'buffer' the IPv4 localuser address for 'uid' */
static void getIPv4(uint32_t *buffer, uint32_t uid)
{
	buffer[0] = get_localuser(uid);
}

/* is 'buffer' pointing a localuser IPv4 address ? */
static int isIPv4(const uint32_t *buffer)
{
	return is_localuser(buffer[0]);
}

/* return the user of the localuser IPv4 pointed by 'buffer' */
static uint32_t uidIPv4(const uint32_t *buffer)
{
	return uid_of_localuser(buffer[0]);
}

/* put in 'buffer' the IPv6 localuser address for 'uid' */
static void getIPv6(uint32_t *buffer, uint32_t uid)
{
	buffer[0] = 0;
	buffer[1] = 0;
	buffer[2] = htonl(0xffff);
	buffer[3] = get_localuser(uid);
}

/* is 'buffer' pointing a localuser IPv6 address ? */
static int isIPv6(const uint32_t *buffer)
{
	return buffer[0] == 0 && buffer[1] == 0
	    && buffer[2] == htonl(0xffff) && is_localuser(buffer[3]);
}

/* return the user of the localuser IPv6 pointed by 'buffer' */
static uint32_t uidIPv6(const uint32_t *buffer)
{
	return uid_of_localuser(buffer[3]);
}

/* fill the output entry */
static enum nss_status fillent(
	const char *name,
	int af,
	struct hostent *result,
	char *buffer,
	size_t buflen,
	int *errnop,
	int *h_errnop,
	uint32_t uid)
{
	int alen = 1 + (int)strlen(name);
	int len = af == AF_INET ? lenip4 : lenip6;

	/* check the family */
	if (af != AF_INET && af != AF_INET6) {
		*errnop = EINVAL;
		*h_errnop = NO_RECOVERY;
		return NSS_STATUS_UNAVAIL;
	}

	/* fill aliases and addr_list */
	if (buflen < 2 * sizeof result->h_aliases[0] + alen + len) {
		*errnop = ERANGE;
		*h_errnop = NO_RECOVERY;
		return NSS_STATUS_TRYAGAIN;
	}

	/* fill the result */
	result->h_addrtype = af;
	result->h_length = len;
	result->h_addr_list = (char**)buffer;
	result->h_addr_list[0] = (char*)&result->h_addr_list[2];
	result->h_name = &result->h_addr_list[0][len];
	result->h_aliases = &result->h_addr_list[1];
	result->h_addr_list[1] = NULL;
	(af == AF_INET ? getIPv4 : getIPv6)((uint32_t*)result->h_addr_list[0], uid);
	memcpy(result->h_name, name, alen);

	return NSS_STATUS_SUCCESS;
}

/* gethostbyname2 implementation for NSS */
enum nss_status _nss_localuser_gethostbyname2_r(
	const char *name,
	int af,
	struct hostent *result,
	char *buffer,
	size_t buflen,
	int *errnop,
	int *h_errnop)
{
	int valid;
	uint32_t uid;
	const char *i;
	char c;

	/* test the name */
	valid = !strncmp(name, localuser, sizeof localuser - 1);
	if (valid) {
		c = name[sizeof localuser - 1];
		if (!c) {
			/* terminated string: use current UID */
			uid = (uint32_t)getuid();
		} else if (c != separator) {
			valid = 0;
		} else {
			/* has a uid specification */
			i = &name[sizeof localuser];
			c = *i;
			valid = '0' <= c && c <= '9';
			if (valid) {
				uid = (uint32_t)(c - '0');
				while ((c = *++i) && (valid = '0' <= c && c <= '9')) {
					uid = (uid << 3) + (uid << 1) + (uint32_t)(c - '0');
				}
				if (valid)
					valid = uid == (uid & locusr_mask);
			}
		}
	}
	if (!valid) {
		*h_errnop = HOST_NOT_FOUND;
		return NSS_STATUS_NOTFOUND;
	}

	/* set default family to IPv4 */
	if (af == AF_UNSPEC)
		af = AF_INET;

	/* fill the result */
	return fillent(name, af, result, buffer, buflen, errnop, h_errnop, uid);
}

/* use gethostbyname2 implementation */
enum nss_status _nss_localuser_gethostbyname_r(
	const char *name,
	struct hostent *result,
	char *buffer,
	size_t buflen,
	int *errnop,
	int *h_errnop)
{
	return _nss_localuser_gethostbyname2_r(name,
					       AF_UNSPEC,
					       result,
					       buffer, buflen, errnop,
					       h_errnop);
}

/* get the name of the address */
enum nss_status _nss_localuser_gethostbyaddr_r(
	const void *addr,
	int len,
	int af,
	struct hostent *result,
	char *buffer,
	size_t buflen,
	int *errnop,
	int *h_errnop)
{
	char c, name[40 + sizeof localuser];
	uint32_t uid, x;
	int l, u;

	/* set default family */
	if (af == AF_UNSPEC) {
		if (len == lenip4)
			af = AF_INET;
		else if (len == lenip6)
			af = AF_INET6;
	}

	/* check whether the IP comforms to localuser */
	if (af == AF_INET && len == lenip4 && isIPv4((const uint32_t*)addr)) {
		/* yes, it's a IPv4, get the uid */
		uid = uidIPv4((const uint32_t*)addr);
	} else if (af == AF_INET6 && len == lenip6 && isIPv6((const uint32_t*)addr)) {
		/* yes, it's a IPv6, get the uid */
		uid = uidIPv6((const uint32_t*)addr);
	} else {
		/* no */
		/* fail */
		*errnop = EINVAL;
		*h_errnop = NO_RECOVERY;
		return NSS_STATUS_NOTFOUND;
	}

	/* build the name */
	memcpy(name, localuser, sizeof localuser - 1);
	if (uid == (uint32_t)getuid())
		name[sizeof localuser - 1] = 0;
	else {
		x = uid;
		name[sizeof localuser - 1] = separator;
		l = u = (int)sizeof localuser;
		do {
			name[u++] = (char)('0' + x % 10);
			x /= 10;
		} while(x);
		name[u--] = 0;
		while (u > l) {
			c = name[u];
			name[u--] = name[l];
			name[l++] = c;
		}
	}
	/* fill the result */
	return fillent(name, af, result, buffer, buflen, errnop, h_errnop, uid);
}