1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 1993, David Greenman
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 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 #include <sys/cdefs.h>
30 __FBSDID("$FreeBSD$");
31
32 #include <sys/param.h>
33 #include <sys/vnode.h>
34 #include <sys/proc.h>
35 #include <sys/sbuf.h>
36 #include <sys/systm.h>
37 #include <sys/sysproto.h>
38 #include <sys/exec.h>
39 #include <sys/imgact.h>
40 #include <sys/kernel.h>
41
42 #if BYTE_ORDER == LITTLE_ENDIAN
43 #define SHELLMAGIC 0x2123 /* #! */
44 #else
45 #define SHELLMAGIC 0x2321
46 #endif
47
48 /*
49 * At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE. This is
50 * significant because the caller has only mapped in one page of the
51 * file we're reading.
52 */
53 #if MAXSHELLCMDLEN > PAGE_SIZE
54 #error "MAXSHELLCMDLEN is larger than a single page!"
55 #endif
56
57 /*
58 * MAXSHELLCMDLEN must be at least MAXINTERP plus the size of the `#!'
59 * prefix and terminating newline.
60 */
61 CTASSERT(MAXSHELLCMDLEN >= MAXINTERP + 3);
62
63 /**
64 * Shell interpreter image activator. An interpreter name beginning at
65 * imgp->args->begin_argv is the minimal successful exit requirement.
66 *
67 * If the given file is a shell-script, then the first line will start
68 * with the two characters `#!' (aka SHELLMAGIC), followed by the name
69 * of the shell-interpreter to run, followed by zero or more tokens.
70 *
71 * The interpreter is then started up such that it will see:
72 * arg[0] -> The name of interpreter as specified after `#!' in the
73 * first line of the script. The interpreter name must
74 * not be longer than MAXSHELLCMDLEN bytes.
75 * arg[1] -> *If* there are any additional tokens on the first line,
76 * then we add a new arg[1], which is a copy of the rest of
77 * that line. The copy starts at the first token after the
78 * interpreter name. We leave it to the interpreter to
79 * parse the tokens in that value.
80 * arg[x] -> the full pathname of the script. This will either be
81 * arg[2] or arg[1], depending on whether or not tokens
82 * were found after the interpreter name.
83 * arg[x+1] -> all the arguments that were specified on the original
84 * command line.
85 *
86 * This processing is described in the execve(2) man page.
87 */
88
89 /*
90 * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
91 * found on the first line of the script, and setup each token as a separate
92 * value in arg[]. This extra processing did not match the behavior of other
93 * OS's, and caused a few subtle problems. For one, it meant the kernel was
94 * deciding how those values should be parsed (wrt characters for quoting or
95 * comments, etc), while the interpreter might have other rules for parsing.
96 * It also meant the interpreter had no way of knowing which arguments came
97 * from the first line of the shell script, and which arguments were specified
98 * by the user on the command line. That extra processing was dropped in the
99 * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
100 */
101 int
102 exec_shell_imgact(struct image_params *imgp)
103 {
104 const char *image_header = imgp->image_header;
105 const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
106 int error, offset;
107 size_t length;
108 struct vattr vattr;
109 struct sbuf *sname;
110
111 /* a shell script? */
112 if (((const short *)image_header)[0] != SHELLMAGIC)
113 return (-1);
114
115 /*
116 * Don't allow a shell script to be the shell for a shell
117 * script. :-)
118 */
119 if (imgp->interpreted & IMGACT_SHELL)
120 return (ENOEXEC);
121
122 imgp->interpreted |= IMGACT_SHELL;
123
124 /*
125 * At this point we have the first page of the file mapped.
126 * However, we don't know how far into the page the contents are
127 * valid -- the actual file might be much shorter than the page.
128 * So find out the file size.
129 */
130 error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred);
131 if (error)
132 return (error);
133
134 /*
135 * Copy shell name and arguments from image_header into a string
136 * buffer.
137 */
138 maxp = &image_header[MIN(vattr.va_size, MAXSHELLCMDLEN)];
139 ihp = &image_header[2];
140
141 /*
142 * Find the beginning and end of the interpreter_name. If the
143 * line does not include any interpreter, or if the name which
144 * was found is too long, we bail out.
145 */
146 while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
147 ihp++;
148 interpb = ihp;
149 while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
150 && (*ihp != '\0')))
151 ihp++;
152 interpe = ihp;
153 if (interpb == interpe)
154 return (ENOEXEC);
155 if (interpe - interpb >= MAXINTERP)
156 return (ENAMETOOLONG);
157
158 /*
159 * Find the beginning of the options (if any), and the end-of-line.
160 * Then trim the trailing blanks off the value. Note that some
161 * other operating systems do *not* trim the trailing whitespace...
162 */
163 while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
164 ihp++;
165 optb = ihp;
166 while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
167 ihp++;
168 opte = ihp;
169 if (opte == maxp)
170 return (ENOEXEC);
171 while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
172 opte = ihp;
173
174 if (imgp->args->fname != NULL) {
175 fname = imgp->args->fname;
176 sname = NULL;
177 } else {
178 sname = sbuf_new_auto();
179 sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
180 sbuf_finish(sname);
181 fname = sbuf_data(sname);
182 }
183
184 /*
185 * We need to "pop" (remove) the present value of arg[0], and "push"
186 * either two or three new values in the arg[] list. To do this,
187 * we first shift all the other values in the `begin_argv' area to
188 * provide the exact amount of room for the values added. Set up
189 * `offset' as the number of bytes to be added to the `begin_argv'
190 * area, and 'length' as the number of bytes being removed.
191 */
192 offset = interpe - interpb + 1; /* interpreter */
193 if (opte > optb) /* options (if any) */
194 offset += opte - optb + 1;
195 offset += strlen(fname) + 1; /* fname of script */
196 length = (imgp->args->argc == 0) ? 0 :
197 strlen(imgp->args->begin_argv) + 1; /* bytes to delete */
198
199 if (offset > imgp->args->stringspace + length) {
200 if (sname != NULL)
201 sbuf_delete(sname);
202 return (E2BIG);
203 }
204
205 bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
206 imgp->args->endp - (imgp->args->begin_argv + length));
207
208 offset -= length; /* calculate actual adjustment */
209 imgp->args->begin_envv += offset;
210 imgp->args->endp += offset;
211 imgp->args->stringspace -= offset;
212
213 /*
214 * If there was no arg[0] when we started, then the interpreter_name
215 * is adding an argument (instead of replacing the arg[0] we started
216 * with). And we're always adding an argument when we include the
217 * full pathname of the original script.
218 */
219 if (imgp->args->argc == 0)
220 imgp->args->argc = 1;
221 imgp->args->argc++;
222
223 /*
224 * The original arg[] list has been shifted appropriately. Copy in
225 * the interpreter name and options-string.
226 */
227 length = interpe - interpb;
228 bcopy(interpb, imgp->args->begin_argv, length);
229 *(imgp->args->begin_argv + length) = '\0';
230 offset = length + 1;
231 if (opte > optb) {
232 length = opte - optb;
233 bcopy(optb, imgp->args->begin_argv + offset, length);
234 *(imgp->args->begin_argv + offset + length) = '\0';
235 offset += length + 1;
236 imgp->args->argc++;
237 }
238
239 /*
240 * Finally, add the filename onto the end for the interpreter to
241 * use and copy the interpreter's name to imgp->interpreter_name
242 * for exec to use.
243 */
244 error = copystr(fname, imgp->args->begin_argv + offset,
245 imgp->args->stringspace, NULL);
246
247 if (error == 0)
248 imgp->interpreter_name = imgp->args->begin_argv;
249
250 if (sname != NULL)
251 sbuf_delete(sname);
252 return (error);
253 }
254
255 /*
256 * Tell kern_execve.c about it, with a little help from the linker.
257 */
258 static struct execsw shell_execsw = {
259 .ex_imgact = exec_shell_imgact,
260 .ex_name = "#!"
261 };
262 EXEC_SET(shell, shell_execsw);
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