1 /* Copyright (C) 1995-2021 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18 #include <alloca.h>
19 #include <errno.h>
20 #include <fcntl.h>
21 #include <unistd.h>
22 #include <netdb.h>
23 #include <not-cancel.h>
24 #include <stdbool.h>
25
26 #define HOSTIDFILE "/etc/hostid"
27
28 #ifdef SET_PROCEDURE
29 int
sethostid(long int id)30 sethostid (long int id)
31 {
32 int fd;
33 ssize_t written;
34 int32_t id32 = id;
35
36 /* Test for appropriate rights to set host ID. */
37 if (__libc_enable_secure)
38 {
39 __set_errno (EPERM);
40 return -1;
41 }
42
43 /* Make sure the ID is not too large. Needed for bi-arch support. */
44 if (id32 != id)
45 {
46 __set_errno (EOVERFLOW);
47 return -1;
48 }
49
50 /* Open file for writing. Everybody is allowed to read this file. */
51 fd = __open_nocancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
52 if (fd < 0)
53 return -1;
54
55 written = __write_nocancel (fd, &id32, sizeof (id32));
56
57 __close_nocancel_nostatus (fd);
58
59 return written != sizeof (id32) ? -1 : 0;
60 }
61
62 #else
63 # include <string.h>
64 # include <sys/param.h>
65 # include <resolv/netdb.h>
66 # include <netinet/in.h>
67 # include <scratch_buffer.h>
68
69 long int
gethostid(void)70 gethostid (void)
71 {
72 char hostname[MAXHOSTNAMELEN + 1];
73 struct hostent hostbuf, *hp;
74 int32_t id;
75 struct in_addr in;
76 int herr;
77 int fd;
78
79 /* First try to get the ID from a former invocation of sethostid. */
80 fd = __open_nocancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
81 if (fd >= 0)
82 {
83 ssize_t n = __read_nocancel (fd, &id, sizeof (id));
84
85 __close_nocancel_nostatus (fd);
86
87 if (n == sizeof (id))
88 return id;
89 }
90
91 /* Getting from the file was not successful. An intelligent guess
92 for a unique number of a host is its IP address. To get the IP
93 address we need to know the host name. */
94 if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
95 /* This also fails. Return and arbitrary value. */
96 return 0;
97
98 /* Determine the IP address of the host name. */
99 struct scratch_buffer tmpbuf;
100 scratch_buffer_init (&tmpbuf);
101 while (true)
102 {
103 int ret = __gethostbyname_r (hostname, &hostbuf,
104 tmpbuf.data, tmpbuf.length, &hp, &herr);
105 if (ret == 0 && hp != NULL)
106 break;
107 else
108 {
109 /* Enlarge the buffer on ERANGE. */
110 if (ret != 0 && herr == NETDB_INTERNAL && errno == ERANGE)
111 {
112 if (!scratch_buffer_grow (&tmpbuf))
113 return 0;
114 }
115 /* Other errors are a failure. Return an arbitrary value. */
116 else
117 {
118 scratch_buffer_free (&tmpbuf);
119 return 0;
120 }
121 }
122 }
123
124 in.s_addr = 0;
125 memcpy (&in, hp->h_addr,
126 (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
127 scratch_buffer_free (&tmpbuf);
128 /* For the return value to be not exactly the IP address we do some
129 bit fiddling. */
130 return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
131 }
132 #endif
133