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comparison contrib/hgsh/hgsh.c @ 2341:dbbe7f72d15a

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contrib: add restricted shell.
author Vadim Gelfer <vadim.gelfer@gmail.com>
date Tue, 23 May 2006 09:33:09 -0700
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children 9cbeef33eaa3
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2338:391c5d0f9ef3 2341:dbbe7f72d15a
1 /*
2 * hgsh.c - restricted login shell for mercurial
3 *
4 * Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>
5 *
6 * This software may be used and distributed according to the terms of the
7 * GNU General Public License, incorporated herein by reference.
8 *
9 * this program is login shell for dedicated mercurial user account. it
10 * only allows few actions:
11 *
12 * 1. run hg in server mode on specific repository. no other hg commands
13 * are allowed. we try to verify that repo to be accessed exists under
14 * given top-level directory.
15 *
16 * 2. (optional) forward ssh connection from firewall/gateway machine to
17 * "real" mercurial host, to let users outside intranet pull and push
18 * changes through firewall.
19 *
20 * 3. (optional) run normal shell, to allow to "su" to mercurial user, use
21 * "sudo" to run programs as that user, or run cron jobs as that user.
22 *
23 * only tested on linux yet. patches for non-linux systems welcome.
24 */
25
26 #ifndef _GNU_SOURCE
27 #define _GNU_SOURCE /* for asprintf */
28 #endif
29
30 #include <stdio.h>
31 #include <stdlib.h>
32 #include <string.h>
33 #include <sys/stat.h>
34 #include <sys/types.h>
35 #include <sysexits.h>
36 #include <unistd.h>
37
38 /*
39 * user config.
40 *
41 * if you see a hostname below, just use first part of hostname. example,
42 * if you have host named foo.bar.com, use "foo".
43 */
44
45 /*
46 * HG_GATEWAY: hostname of gateway/firewall machine that people outside your
47 * intranet ssh into if they need to ssh to other machines. if you do not
48 * have such machine, set to NULL.
49 */
50 #ifndef HG_GATEWAY
51 #define HG_GATEWAY "gateway"
52 #endif
53
54 /*
55 * HG_HOST: hostname of mercurial server. if any machine is allowed, set to
56 * NULL.
57 */
58 #ifndef HG_HOST
59 #define HG_HOST "mercurial"
60 #endif
61
62 /*
63 * HG_USER: username to log in from HG_GATEWAY to HG_HOST. if gateway and
64 * host username are same, set to NULL.
65 */
66 #ifndef HG_USER
67 #define HG_USER "hg"
68 #endif
69
70 /*
71 * HG_ROOT: root of tree full of mercurial repos. if you do not want to
72 * validate location of repo when someone is try to access, set to NULL.
73 */
74 #ifndef HG_ROOT
75 #define HG_ROOT "/home/hg/repos"
76 #endif
77
78 /*
79 * HG: path to the mercurial executable to run.
80 */
81 #ifndef HG
82 #define HG "/home/hg/bin/hg"
83 #endif
84
85 /*
86 * HG_SHELL: shell to use for actions like "sudo" and "su" access to
87 * mercurial user, and cron jobs. if you want to make these things
88 * impossible, set to NULL.
89 */
90 #ifndef HG_SHELL
91 #define HG_SHELL NULL
92 // #define HG_SHELL "/bin/bash"
93 #endif
94
95 /*
96 * HG_HELP: some way for users to get support if they have problem. if they
97 * should not get helpful message, set to NULL.
98 */
99 #ifndef HG_HELP
100 #define HG_HELP "please contact support@example.com for help."
101 #endif
102
103 /*
104 * SSH: path to ssh executable to run, if forwarding from HG_GATEWAY to
105 * HG_HOST. if you want to use rsh instead (why?), you need to modify
106 * arguments it is called with. see forward_through_gateway.
107 */
108 #ifndef SSH
109 #define SSH "/usr/bin/ssh"
110 #endif
111
112 /*
113 * tell whether to print command that is to be executed. useful for
114 * debugging. should not interfere with mercurial operation, since
115 * mercurial only cares about stdin and stdout, and this prints to stderr.
116 */
117 static const int debug = 0;
118
119 static void print_cmdline(int argc, char **argv)
120 {
121 FILE *fp = stderr;
122 int i;
123
124 fputs("command: ", fp);
125
126 for (i = 0; i < argc; i++) {
127 char *spc = strpbrk(argv[i], " \t\r\n");
128 if (spc) {
129 fputc('\'', fp);
130 }
131 fputs(argv[i], fp);
132 if (spc) {
133 fputc('\'', fp);
134 }
135 if (i < argc - 1) {
136 fputc(' ', fp);
137 }
138 }
139 fputc('\n', fp);
140 fflush(fp);
141 }
142
143 static void usage(const char *reason, int exitcode)
144 {
145 char *hg_help = HG_HELP;
146
147 if (reason) {
148 fprintf(stderr, "*** Error: %s.\n", reason);
149 }
150 fprintf(stderr, "*** This program has been invoked incorrectly.\n");
151 if (hg_help) {
152 fprintf(stderr, "*** %s\n", hg_help);
153 }
154 exit(exitcode ? exitcode : EX_USAGE);
155 }
156
157 /*
158 * run on gateway host to make another ssh connection, to "real" mercurial
159 * server. it sends its command line unmodified to far end.
160 *
161 * never called if HG_GATEWAY is NULL.
162 */
163 static void forward_through_gateway(int argc, char **argv)
164 {
165 char *ssh = SSH;
166 char *hg_host = HG_HOST;
167 char *hg_user = HG_USER;
168 char **nargv = alloca((10 + argc) * sizeof(char *));
169 int i = 0, j;
170
171 nargv[i++] = ssh;
172 nargv[i++] = "-q";
173 nargv[i++] = "-T";
174 nargv[i++] = "-x";
175 if (hg_user) {
176 nargv[i++] = "-l";
177 nargv[i++] = hg_user;
178 }
179 nargv[i++] = hg_host;
180
181 /*
182 * sshd called us with added "-c", because it thinks we are a shell.
183 * drop it if we find it.
184 */
185 j = 1;
186 if (j < argc && strcmp(argv[j], "-c") == 0) {
187 j++;
188 }
189
190 for (; j < argc; i++, j++) {
191 nargv[i] = argv[j];
192 }
193 nargv[i] = NULL;
194
195 if (debug) {
196 print_cmdline(i, nargv);
197 }
198
199 execv(ssh, nargv);
200 perror(ssh);
201 exit(EX_UNAVAILABLE);
202 }
203
204 /*
205 * run shell. let administrator "su" to mercurial user's account to do
206 * administrative works.
207 *
208 * never called if HG_SHELL is NULL.
209 */
210 static void run_shell(int argc, char **argv)
211 {
212 char *hg_shell = HG_SHELL;
213 char **nargv;
214 char *c;
215 int i;
216
217 nargv = alloca((argc + 3) * sizeof(char *));
218 c = strrchr(hg_shell, '/');
219
220 /* tell "real" shell it is login shell, if needed. */
221
222 if (argv[0][0] == '-' && c) {
223 nargv[0] = strdup(c);
224 if (nargv[0] == NULL) {
225 perror("malloc");
226 exit(EX_OSERR);
227 }
228 nargv[0][0] = '-';
229 } else {
230 nargv[0] = hg_shell;
231 }
232
233 for (i = 1; i < argc; i++) {
234 nargv[i] = argv[i];
235 }
236 nargv[i] = NULL;
237
238 if (debug) {
239 print_cmdline(i, nargv);
240 }
241
242 execv(hg_shell, nargv);
243 perror(hg_shell);
244 exit(EX_OSFILE);
245 }
246
247 /*
248 * paranoid wrapper, runs hg executable in server mode.
249 */
250 static void serve_data(int argc, char **argv)
251 {
252 char *hg_root = HG_ROOT;
253 char *repo, *abspath;
254 char *nargv[6];
255 struct stat st;
256 size_t repolen;
257 int i;
258
259 /*
260 * check argv for looking okay. we should be invoked with argv
261 * resembling like this:
262 *
263 * hgsh
264 * -c
265 * hg -R some/path serve --stdio
266 *
267 * the "-c" is added by sshd, because it thinks we are login shell.
268 */
269
270 if (argc != 3) {
271 goto badargs;
272 }
273
274 if (strcmp(argv[1], "-c") != 0) {
275 goto badargs;
276 }
277
278 if (sscanf(argv[2], "hg -R %as serve --stdio", &repo) != 1) {
279 goto badargs;
280 }
281
282 repolen = repo ? strlen(repo) : 0;
283
284 if (repolen == 0) {
285 goto badargs;
286 }
287
288 if (hg_root) {
289 if (asprintf(&abspath, "%s/%s/.hg/data", hg_root, repo) == -1) {
290 goto badargs;
291 }
292
293 /*
294 * attempt to stop break out from inside the repository tree. could
295 * do something more clever here, because e.g. we could traverse a
296 * symlink that looks safe, but really breaks us out of tree.
297 */
298
299 if (strstr(abspath, "/../") != NULL) {
300 goto badargs;
301 }
302
303 /* verify that we really are looking at valid repo. */
304
305 if (stat(abspath, &st) == -1) {
306 perror(repo);
307 exit(EX_DATAERR);
308 }
309
310 if (chdir(hg_root) == -1) {
311 perror(hg_root);
312 exit(EX_SOFTWARE);
313 }
314 }
315
316 i = 0;
317 nargv[i++] = HG;
318 nargv[i++] = "-R";
319 nargv[i++] = repo;
320 nargv[i++] = "serve";
321 nargv[i++] = "--stdio";
322 nargv[i] = NULL;
323
324 if (debug) {
325 print_cmdline(i, nargv);
326 }
327
328 execv(HG, nargv);
329 perror(HG);
330 exit(EX_UNAVAILABLE);
331
332 badargs:
333 /* print useless error message. */
334
335 usage("invalid arguments", EX_DATAERR);
336 }
337
338 int main(int argc, char **argv)
339 {
340 char host[1024];
341 char *c;
342
343 if (gethostname(host, sizeof(host)) == -1) {
344 perror("gethostname");
345 exit(EX_OSERR);
346 }
347
348 if ((c = strchr(host, '.')) != NULL) {
349 *c = '\0';
350 }
351
352 if (getenv("SSH_CLIENT")) {
353 char *hg_gateway = HG_GATEWAY;
354 char *hg_host = HG_HOST;
355
356 if (hg_gateway && strcmp(host, hg_gateway) == 0) {
357 forward_through_gateway(argc, argv);
358 }
359
360 if (hg_host && strcmp(host, hg_host) != 0) {
361 usage("invoked on unexpected host", EX_USAGE);
362 }
363
364 serve_data(argc, argv);
365 } else if (HG_SHELL) {
366 run_shell(argc, argv);
367 } else {
368 usage("invalid arguments", EX_DATAERR);
369 }
370
371 return 0;
372 }