1 /* $NetBSD: exec_script.c,v 1.85 2024/12/06 16:19:41 riastradh Exp $ */
2
3 /*
4 * Copyright (c) 1993, 1994, 1996 Christopher G. Demetriou
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. All advertising materials mentioning features or use of this software
16 * must display the following acknowledgement:
17 * This product includes software developed by Christopher G. Demetriou.
18 * 4. The name of the author may not be used to endorse or promote products
19 * derived from this software without specific prior written permission
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
22 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
23 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
24 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
25 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
26 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
27 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
28 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
29 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
30 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31 */
32
33 #include <sys/cdefs.h>
34 __KERNEL_RCSID(0, "$NetBSD: exec_script.c,v 1.85 2024/12/06 16:19:41 riastradh Exp $");
35
36 #ifdef _KERNEL_OPT
37 #include "opt_script.h"
38 #endif
39
40 #if defined(SETUIDSCRIPTS) && !defined(FDSCRIPTS)
41 #define FDSCRIPTS /* Need this for safe set-id scripts. */
42 #endif
43
44 #include <sys/param.h>
45 #include <sys/types.h>
46
47 #include <sys/exec.h>
48 #include <sys/exec_elf.h>
49 #include <sys/exec_script.h>
50 #include <sys/file.h>
51 #include <sys/filedesc.h>
52 #include <sys/kmem.h>
53 #include <sys/module.h>
54 #include <sys/namei.h>
55 #include <sys/proc.h>
56 #include <sys/resourcevar.h>
57 #include <sys/sdt.h>
58 #ifdef SETUIDSCRIPTS
59 #include <sys/stat.h>
60 #endif
61 #include <sys/systm.h>
62 #include <sys/vnode.h>
63
64 MODULE(MODULE_CLASS_EXEC, exec_script, NULL);
65
66 static struct execsw exec_script_execsw = {
67 .es_hdrsz = SCRIPT_HDR_SIZE,
68 .es_makecmds = exec_script_makecmds,
69 .u = {
70 .elf_probe_func = NULL,
71 },
72 .es_emul = NULL,
73 .es_prio = EXECSW_PRIO_ANY,
74 .es_arglen = 0,
75 .es_copyargs = NULL,
76 .es_setregs = NULL,
77 .es_coredump = NULL,
78 .es_setup_stack = exec_setup_stack,
79 };
80
81 static int
exec_script_modcmd(modcmd_t cmd,void * arg)82 exec_script_modcmd(modcmd_t cmd, void *arg)
83 {
84
85 switch (cmd) {
86 case MODULE_CMD_INIT:
87 return exec_add(&exec_script_execsw, 1);
88
89 case MODULE_CMD_FINI:
90 return exec_remove(&exec_script_execsw, 1);
91
92 case MODULE_CMD_AUTOUNLOAD:
93 /*
94 * We don't want to be autounloaded because our use is
95 * transient: no executables with p_execsw equal to
96 * exec_script_execsw will exist, so FINI will never
97 * return EBUSY. However, the system will run scripts
98 * often. Return EBUSY here to prevent this module from
99 * ping-ponging in and out of the kernel.
100 */
101 return SET_ERROR(EBUSY);
102
103 default:
104 return SET_ERROR(ENOTTY);
105 }
106 }
107
108 /*
109 * exec_script_makecmds(): Check if it's an executable shell script.
110 *
111 * Given a proc pointer and an exec package pointer, see if the referent
112 * of the epp is in shell script. If it is, then set thing up so that
113 * the script can be run. This involves preparing the address space
114 * and arguments for the shell which will run the script.
115 *
116 * This function is ultimately responsible for creating a set of vmcmds
117 * which can be used to build the process's vm space and inserting them
118 * into the exec package.
119 */
120 int
exec_script_makecmds(struct lwp * l,struct exec_package * epp)121 exec_script_makecmds(struct lwp *l, struct exec_package *epp)
122 {
123 int error, hdrlinelen, shellnamelen, shellarglen;
124 char *hdrstr = epp->ep_hdr;
125 char *cp, *shellname, *shellarg;
126 size_t shellargp_len;
127 struct exec_fakearg *shellargp;
128 struct exec_fakearg *tmpsap;
129 struct pathbuf *shell_pathbuf;
130 struct vnode *scriptvp;
131 #ifdef SETUIDSCRIPTS
132 /* Gcc needs those initialized for spurious uninitialized warning */
133 uid_t script_uid = (uid_t) -1;
134 gid_t script_gid = NOGROUP;
135 u_short script_sbits;
136 #endif
137
138 /*
139 * if the magic isn't that of a shell script, or we've already
140 * done shell script processing for this exec, punt on it.
141 */
142 if ((epp->ep_flags & EXEC_INDIR) != 0 ||
143 epp->ep_hdrvalid < EXEC_SCRIPT_MAGICLEN ||
144 strncmp(hdrstr, EXEC_SCRIPT_MAGIC, EXEC_SCRIPT_MAGICLEN))
145 return SET_ERROR(ENOEXEC);
146
147 /*
148 * Check that the shell spec is terminated by a newline, and that
149 * it isn't too large.
150 */
151 hdrlinelen = uimin(epp->ep_hdrvalid, SCRIPT_HDR_SIZE);
152 for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; cp < hdrstr + hdrlinelen;
153 cp++) {
154 if (*cp == '\n') {
155 *cp = '\0';
156 break;
157 }
158 }
159 if (cp >= hdrstr + hdrlinelen)
160 return SET_ERROR(ENOEXEC);
161
162 /* strip spaces before the shell name */
163 for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; *cp == ' ' || *cp == '\t';
164 cp++)
165 ;
166 if (*cp == '\0')
167 return SET_ERROR(ENOEXEC);
168
169 shellarg = NULL;
170 shellarglen = 0;
171
172 /* collect the shell name; remember its length for later */
173 shellname = cp;
174 shellnamelen = 0;
175 for ( /* cp = cp */ ; *cp != '\0' && *cp != ' ' && *cp != '\t'; cp++)
176 shellnamelen++;
177 if (*cp == '\0')
178 goto check_shell;
179 *cp++ = '\0';
180
181 /* skip spaces before any argument */
182 for ( /* cp = cp */ ; *cp == ' ' || *cp == '\t'; cp++)
183 ;
184 if (*cp == '\0')
185 goto check_shell;
186
187 /*
188 * collect the shell argument. everything after the shell name
189 * is passed as ONE argument; that's the correct (historical)
190 * behaviour.
191 */
192 shellarg = cp;
193 for ( /* cp = cp */ ; *cp != '\0'; cp++)
194 shellarglen++;
195 *cp++ = '\0';
196
197 check_shell:
198 #ifdef SETUIDSCRIPTS
199 /*
200 * MNT_NOSUID has already taken care of by check_exec,
201 * so we don't need to worry about it now or later. We
202 * will need to check PSL_TRACED later, however.
203 */
204 script_sbits = epp->ep_vap->va_mode & (S_ISUID | S_ISGID);
205 if (script_sbits != 0) {
206 script_uid = epp->ep_vap->va_uid;
207 script_gid = epp->ep_vap->va_gid;
208 }
209 #endif
210 #ifdef FDSCRIPTS
211 /*
212 * if the script isn't readable, or it's set-id, then we've
213 * gotta supply a "/dev/fd/..." for the shell to read.
214 * Note that stupid shells (csh) do the wrong thing, and
215 * close all open fd's when they start. That kills this
216 * method of implementing "safe" set-id and x-only scripts.
217 */
218 vn_lock(epp->ep_vp, LK_SHARED | LK_RETRY);
219 error = VOP_ACCESS(epp->ep_vp, VREAD, l->l_cred);
220 VOP_UNLOCK(epp->ep_vp);
221 if (error == EACCES
222 #ifdef SETUIDSCRIPTS
223 || script_sbits
224 #endif
225 ) {
226 struct file *fp;
227
228 KASSERT(!(epp->ep_flags & EXEC_HASFD));
229
230 if ((error = fd_allocfile(&fp, &epp->ep_fd)) != 0) {
231 scriptvp = NULL;
232 shellargp = NULL;
233 goto fail;
234 }
235 epp->ep_flags |= EXEC_HASFD;
236 fp->f_type = DTYPE_VNODE;
237 fp->f_ops = &vnops;
238 fp->f_vnode = epp->ep_vp;
239 fp->f_flag = FREAD;
240 fd_affix(curproc, fp, epp->ep_fd);
241 }
242 #endif
243
244 /* set up the fake args list */
245 shellargp_len = 4 * sizeof(*shellargp);
246 shellargp = kmem_alloc(shellargp_len, KM_SLEEP);
247 tmpsap = shellargp;
248 tmpsap->fa_len = shellnamelen + 1;
249 tmpsap->fa_arg = kmem_alloc(tmpsap->fa_len, KM_SLEEP);
250 strlcpy(tmpsap->fa_arg, shellname, tmpsap->fa_len);
251 tmpsap++;
252 if (shellarg != NULL) {
253 tmpsap->fa_len = shellarglen + 1;
254 tmpsap->fa_arg = kmem_alloc(tmpsap->fa_len, KM_SLEEP);
255 strlcpy(tmpsap->fa_arg, shellarg, tmpsap->fa_len);
256 tmpsap++;
257 }
258 tmpsap->fa_len = MAXPATHLEN;
259 tmpsap->fa_arg = kmem_alloc(tmpsap->fa_len, KM_SLEEP);
260 #ifdef FDSCRIPTS
261 if ((epp->ep_flags & EXEC_HASFD) == 0) {
262 #endif
263 /* normally can't fail, but check for it if diagnostic */
264 error = copystr(epp->ep_kname, tmpsap->fa_arg, MAXPATHLEN,
265 NULL);
266 KASSERT(error == 0);
267 tmpsap++;
268 #ifdef FDSCRIPTS
269 } else {
270 snprintf(tmpsap->fa_arg, MAXPATHLEN, "/dev/fd/%d", epp->ep_fd);
271 tmpsap++;
272 }
273 #endif
274 tmpsap->fa_arg = NULL;
275
276 /* Save the old vnode so we can clean it up later. */
277 scriptvp = epp->ep_vp;
278 epp->ep_vp = NULL;
279
280 /* Note that we're trying recursively. */
281 epp->ep_flags |= EXEC_INDIR;
282
283 /*
284 * mark the header we have as invalid; check_exec will read
285 * the header from the new executable
286 */
287 epp->ep_hdrvalid = 0;
288
289 /* try loading the interpreter */
290 if ((error = exec_makepathbuf(l, shellname, UIO_SYSSPACE,
291 &shell_pathbuf, NULL)) == 0) {
292 error = check_exec(l, epp, shell_pathbuf, NULL);
293 pathbuf_destroy(shell_pathbuf);
294 }
295
296 /* note that we've clobbered the header */
297 epp->ep_flags |= EXEC_DESTR;
298
299 if (error == 0) {
300 /*
301 * It succeeded. Unlock the script and
302 * close it if we aren't using it any more.
303 * Also, set things up so that the fake args
304 * list will be used.
305 */
306 if ((epp->ep_flags & EXEC_HASFD) == 0) {
307 vn_lock(scriptvp, LK_EXCLUSIVE | LK_RETRY);
308 VOP_CLOSE(scriptvp, FREAD, l->l_cred);
309 vput(scriptvp);
310 }
311
312 epp->ep_flags |= (EXEC_HASARGL | EXEC_SKIPARG);
313 epp->ep_fa = shellargp;
314 epp->ep_fa_len = shellargp_len;
315 #ifdef SETUIDSCRIPTS
316 /*
317 * set thing up so that set-id scripts will be
318 * handled appropriately. PSL_TRACED will be
319 * checked later when the shell is actually
320 * exec'd.
321 */
322 epp->ep_vap->va_mode |= script_sbits;
323 if (script_sbits & S_ISUID)
324 epp->ep_vap->va_uid = script_uid;
325 if (script_sbits & S_ISGID)
326 epp->ep_vap->va_gid = script_gid;
327 #endif
328 return (0);
329 }
330
331 #ifdef FDSCRIPTS
332 fail:
333 #endif
334
335 /* kill the opened file descriptor, else close the file */
336 if (epp->ep_flags & EXEC_HASFD) {
337 epp->ep_flags &= ~EXEC_HASFD;
338 fd_close(epp->ep_fd);
339 } else if (scriptvp) {
340 vn_lock(scriptvp, LK_EXCLUSIVE | LK_RETRY);
341 VOP_CLOSE(scriptvp, FREAD, l->l_cred);
342 vput(scriptvp);
343 }
344
345 /* free the fake arg list, because we're not returning it */
346 if ((tmpsap = shellargp) != NULL) {
347 while (tmpsap->fa_arg != NULL) {
348 kmem_free(tmpsap->fa_arg, tmpsap->fa_len);
349 tmpsap++;
350 }
351 kmem_free(shellargp, shellargp_len);
352 }
353
354 /*
355 * free any vmspace-creation commands,
356 * and release their references
357 */
358 kill_vmcmds(&epp->ep_vmcmds);
359
360 return error;
361 }
362