1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * linux/fs/binfmt_script.c
4 *
5 * Copyright (C) 1996 Martin von Löwis
6 * original #!-checking implemented by tytso.
7 */
8
9 #include <linux/module.h>
10 #include <linux/string.h>
11 #include <linux/stat.h>
12 #include <linux/binfmts.h>
13 #include <linux/init.h>
14 #include <linux/file.h>
15 #include <linux/err.h>
16 #include <linux/fs.h>
17
18 static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
19 static inline char *next_non_spacetab(char *first, const char *last)
20 {
21 for (; first <= last; first++)
22 if (!spacetab(*first))
23 return first;
24 return NULL;
25 }
26 static inline char *next_terminator(char *first, const char *last)
27 {
28 for (; first <= last; first++)
29 if (spacetab(*first) || !*first)
30 return first;
31 return NULL;
32 }
33
34 static int load_script(struct linux_binprm *bprm)
35 {
36 const char *i_arg, *i_name;
37 char *cp, *buf_end;
38 struct file *file;
39 int retval;
40
41 /* Not ours to exec if we don't start with "#!". */
42 if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
43 return -ENOEXEC;
44
45 /*
46 * If the script filename will be inaccessible after exec, typically
47 * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give
48 * up now (on the assumption that the interpreter will want to load
49 * this file).
50 */
51 if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
52 return -ENOENT;
53
54 /* Release since we are not mapping a binary into memory. */
55 allow_write_access(bprm->file);
56 fput(bprm->file);
57 bprm->file = NULL;
58
59 /*
60 * This section handles parsing the #! line into separate
61 * interpreter path and argument strings. We must be careful
62 * because bprm->buf is not yet guaranteed to be NUL-terminated
63 * (though the buffer will have trailing NUL padding when the
64 * file size was smaller than the buffer size).
65 *
66 * We do not want to exec a truncated interpreter path, so either
67 * we find a newline (which indicates nothing is truncated), or
68 * we find a space/tab/NUL after the interpreter path (which
69 * itself may be preceded by spaces/tabs). Truncating the
70 * arguments is fine: the interpreter can re-read the script to
71 * parse them on its own.
72 */
73 buf_end = bprm->buf + sizeof(bprm->buf) - 1;
74 cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
75 if (!cp) {
76 cp = next_non_spacetab(bprm->buf + 2, buf_end);
77 if (!cp)
78 return -ENOEXEC; /* Entire buf is spaces/tabs */
79 /*
80 * If there is no later space/tab/NUL we must assume the
81 * interpreter path is truncated.
82 */
83 if (!next_terminator(cp, buf_end))
84 return -ENOEXEC;
85 cp = buf_end;
86 }
87 /* NUL-terminate the buffer and any trailing spaces/tabs. */
88 *cp = '\0';
89 while (cp > bprm->buf) {
90 cp--;
91 if ((*cp == ' ') || (*cp == '\t'))
92 *cp = '\0';
93 else
94 break;
95 }
96 for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
97 if (*cp == '\0')
98 return -ENOEXEC; /* No interpreter name found */
99 i_name = cp;
100 i_arg = NULL;
101 for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++)
102 /* nothing */ ;
103 while ((*cp == ' ') || (*cp == '\t'))
104 *cp++ = '\0';
105 if (*cp)
106 i_arg = cp;
107 /*
108 * OK, we've parsed out the interpreter name and
109 * (optional) argument.
110 * Splice in (1) the interpreter's name for argv[0]
111 * (2) (optional) argument to interpreter
112 * (3) filename of shell script (replace argv[0])
113 *
114 * This is done in reverse order, because of how the
115 * user environment and arguments are stored.
116 */
117 retval = remove_arg_zero(bprm);
118 if (retval)
119 return retval;
120 retval = copy_strings_kernel(1, &bprm->interp, bprm);
121 if (retval < 0)
122 return retval;
123 bprm->argc++;
124 if (i_arg) {
125 retval = copy_strings_kernel(1, &i_arg, bprm);
126 if (retval < 0)
127 return retval;
128 bprm->argc++;
129 }
130 retval = copy_strings_kernel(1, &i_name, bprm);
131 if (retval)
132 return retval;
133 bprm->argc++;
134 retval = bprm_change_interp(i_name, bprm);
135 if (retval < 0)
136 return retval;
137
138 /*
139 * OK, now restart the process with the interpreter's dentry.
140 */
141 file = open_exec(i_name);
142 if (IS_ERR(file))
143 return PTR_ERR(file);
144
145 bprm->file = file;
146 retval = prepare_binprm(bprm);
147 if (retval < 0)
148 return retval;
149 return search_binary_handler(bprm);
150 }
151
152 static struct linux_binfmt script_format = {
153 .module = THIS_MODULE,
154 .load_binary = load_script,
155 };
156
157 static int __init init_script_binfmt(void)
158 {
159 register_binfmt(&script_format);
160 return 0;
161 }
162
163 static void __exit exit_script_binfmt(void)
164 {
165 unregister_binfmt(&script_format);
166 }
167
168 core_initcall(init_script_binfmt);
169 module_exit(exit_script_binfmt);
170 MODULE_LICENSE("GPL");