1 /* $NetBSD: unix_send_fd.c,v 1.8 2023/12/23 20:30:46 christos Exp $ */
2
3 /*++
4 /* NAME
5 /* unix_send_fd 3
6 /* SUMMARY
7 /* send file descriptor
8 /* SYNOPSIS
9 /* #include <iostuff.h>
10 /*
11 /* int unix_send_fd(fd, sendfd)
12 /* int fd;
13 /* int sendfd;
14 /* DESCRIPTION
15 /* unix_send_fd() sends a file descriptor over the specified
16 /* UNIX-domain socket.
17 /*
18 /* Arguments:
19 /* .IP fd
20 /* File descriptor that connects the sending and receiving processes.
21 /* .IP sendfd
22 /* The file descriptor to be sent.
23 /* DIAGNOSTICS
24 /* unix_send_fd() returns -1 upon failure.
25 /* LICENSE
26 /* .ad
27 /* .fi
28 /* The Secure Mailer license must be distributed with this software.
29 /* AUTHOR(S)
30 /* Wietse Venema
31 /* IBM T.J. Watson Research
32 /* P.O. Box 704
33 /* Yorktown Heights, NY 10598, USA
34 /*
35 /* Wietse Venema
36 /* Google, Inc.
37 /* 111 8th Avenue
38 /* New York, NY 10011, USA
39 /*--*/
40
41 /* System library. */
42
43 #include <sys_defs.h> /* includes <sys/types.h> */
44 #include <sys/socket.h>
45 #include <sys/uio.h>
46 #include <string.h>
47
48 /* Utility library. */
49
50 #include <msg.h>
51 #include <iostuff.h>
52
53 /* unix_send_fd - send file descriptor */
54
unix_send_fd(int fd,int sendfd)55 int unix_send_fd(int fd, int sendfd)
56 {
57
58 /*
59 * This code does not work with version <2.2 Linux kernels, and it does
60 * not compile with version <2 Linux libraries.
61 */
62 #ifdef CANT_USE_SEND_RECV_MSG
63 const char *myname = "unix_send_fd";
64
65 msg_warn("%s: your system has no support for file descriptor passing",
66 myname);
67 return (-1);
68 #else
69 struct msghdr msg;
70 struct iovec iov[1];
71
72 /*
73 * Adapted from: W. Richard Stevens, UNIX Network Programming, Volume 1,
74 * Second edition. Except that we use CMSG_LEN instead of CMSG_SPACE, for
75 * portability to some LP64 environments. See also unix_recv_fd.c.
76 */
77 #if defined(CMSG_SPACE) && !defined(NO_MSGHDR_MSG_CONTROL)
78 union {
79 struct cmsghdr just_for_alignment;
80 char control[CMSG_SPACE(sizeof(sendfd))];
81 } control_un;
82 struct cmsghdr *cmptr;
83
84 memset((void *) &msg, 0, sizeof(msg)); /* Fix 200512 */
85 memset((void *) &control_un, 0, sizeof(control_un)); /* Fix 202302 */
86 msg.msg_control = control_un.control;
87 if (unix_pass_fd_fix & UNIX_PASS_FD_FIX_CMSG_LEN) {
88 msg.msg_controllen = CMSG_LEN(sizeof(sendfd)); /* Fix 200506 */
89 } else {
90 msg.msg_controllen = CMSG_SPACE(sizeof(sendfd)); /* normal */
91 }
92 cmptr = CMSG_FIRSTHDR(&msg);
93 cmptr->cmsg_len = CMSG_LEN(sizeof(sendfd));
94 cmptr->cmsg_level = SOL_SOCKET;
95 cmptr->cmsg_type = SCM_RIGHTS;
96 *(int *) CMSG_DATA(cmptr) = sendfd;
97 #else
98 msg.msg_accrights = (char *) &sendfd;
99 msg.msg_accrightslen = sizeof(sendfd);
100 #endif
101
102 msg.msg_name = 0;
103 msg.msg_namelen = 0;
104
105 /*
106 * XXX We don't want to pass any data, just a file descriptor. However,
107 * setting msg.msg_iov = 0 and msg.msg_iovlen = 0 causes trouble. See the
108 * comments in the unix_recv_fd() routine.
109 */
110 iov->iov_base = "";
111 iov->iov_len = 1;
112 msg.msg_iov = iov;
113 msg.msg_iovlen = 1;
114
115 /*
116 * The CMSG_LEN send/receive workaround was originally developed for
117 * OpenBSD 3.6 on SPARC64. After the workaround was verified to not break
118 * Solaris 8 on SPARC64, it was hard-coded with Postfix 2.3 for all
119 * platforms because of increasing pressure to work on other things. The
120 * workaround does nothing for 32-bit systems.
121 *
122 * The investigation was reopened with Postfix 2.7 because the workaround
123 * broke with NetBSD 5.0 on 64-bit architectures. This time it was found
124 * that OpenBSD <= 4.3 on AMD64 and SPARC64 needed the workaround for
125 * sending only. The following platforms worked with and without the
126 * workaround: OpenBSD 4.5 on AMD64 and SPARC64, FreeBSD 7.2 on AMD64,
127 * Solaris 8 on SPARC64, and Linux 2.6-11 on x86_64.
128 *
129 * As this appears to have been an OpenBSD-specific problem, we revert to
130 * the Postfix 2.2 behavior. Instead of hard-coding the workaround for
131 * all platforms, we now detect sendmsg() errors at run time and turn on
132 * the workaround dynamically.
133 *
134 * The workaround was made run-time configurable to investigate the problem
135 * on multiple platforms. Though set_unix_pass_fd_fix() is over-kill for
136 * this specific problem, it is left in place so that it can serve as an
137 * example of how to add run-time configurable workarounds to Postfix.
138 */
139 if (sendmsg(fd, &msg, 0) >= 0)
140 return (0);
141 if (unix_pass_fd_fix == 0) {
142 if (msg_verbose)
143 msg_info("sendmsg error (%m). Trying CMSG_LEN workaround.");
144 unix_pass_fd_fix = UNIX_PASS_FD_FIX_CMSG_LEN;
145 return (unix_send_fd(fd, sendfd));
146 } else {
147 return (-1);
148 }
149 #endif
150 }
151
152 #ifdef TEST
153
154 /*
155 * Proof-of-concept program. Open a file and send the descriptor, presumably
156 * to the unix_recv_fd test program.
157 */
158 #include <unistd.h>
159 #include <string.h>
160 #include <stdlib.h>
161 #include <fcntl.h>
162 #include <split_at.h>
163 #include <connect.h>
164
main(int argc,char ** argv)165 int main(int argc, char **argv)
166 {
167 char *transport;
168 char *endpoint;
169 char *path;
170 int server_sock;
171 int client_fd;
172
173 msg_verbose = 1;
174
175 if (argc < 3
176 || (endpoint = split_at(transport = argv[1], ':')) == 0
177 || *endpoint == 0 || *transport == 0)
178 msg_fatal("usage: %s transport:endpoint file...", argv[0]);
179
180 if (strcmp(transport, "unix") == 0) {
181 server_sock = unix_connect(endpoint, BLOCKING, 0);
182 } else {
183 msg_fatal("invalid transport name: %s", transport);
184 }
185 if (server_sock < 0)
186 msg_fatal("connect %s:%s: %m", transport, endpoint);
187
188 argv += 2;
189 while ((path = *argv++) != 0) {
190 if ((client_fd = open(path, O_RDONLY, 0)) < 0)
191 msg_fatal("open %s: %m", path);
192 msg_info("path=%s fd=%d", path, client_fd);
193 if (unix_send_fd(server_sock, client_fd) < 0)
194 msg_fatal("send file descriptor: %m");
195 if (close(client_fd) != 0)
196 msg_fatal("close(%d): %m", client_fd);
197 }
198 exit(0);
199 }
200
201 #endif
202