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 const char *next_non_spacetab(const 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 const char *next_terminator(const 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_name, *i_sep, *i_arg, *i_end, *buf_end;
37 struct file *file;
38 int retval;
39
40 /* Not ours to exec if we don't start with "#!". */
41 if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
42 return -ENOEXEC;
43
44 /*
45 * This section handles parsing the #! line into separate
46 * interpreter path and argument strings. We must be careful
47 * because bprm->buf is not yet guaranteed to be NUL-terminated
48 * (though the buffer will have trailing NUL padding when the
49 * file size was smaller than the buffer size).
50 *
51 * We do not want to exec a truncated interpreter path, so either
52 * we find a newline (which indicates nothing is truncated), or
53 * we find a space/tab/NUL after the interpreter path (which
54 * itself may be preceded by spaces/tabs). Truncating the
55 * arguments is fine: the interpreter can re-read the script to
56 * parse them on its own.
57 */
58 buf_end = bprm->buf + sizeof(bprm->buf) - 1;
59 i_end = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
60 if (!i_end) {
61 i_end = next_non_spacetab(bprm->buf + 2, buf_end);
62 if (!i_end)
63 return -ENOEXEC; /* Entire buf is spaces/tabs */
64 /*
65 * If there is no later space/tab/NUL we must assume the
66 * interpreter path is truncated.
67 */
68 if (!next_terminator(i_end, buf_end))
69 return -ENOEXEC;
70 i_end = buf_end;
71 }
72 /* Trim any trailing spaces/tabs from i_end */
73 while (spacetab(i_end[-1]))
74 i_end--;
75
76 /* Skip over leading spaces/tabs */
77 i_name = next_non_spacetab(bprm->buf+2, i_end);
78 if (!i_name || (i_name == i_end))
79 return -ENOEXEC; /* No interpreter name found */
80
81 /* Is there an optional argument? */
82 i_arg = NULL;
83 i_sep = next_terminator(i_name, i_end);
84 if (i_sep && (*i_sep != '\0'))
85 i_arg = next_non_spacetab(i_sep, i_end);
86
87 /*
88 * If the script filename will be inaccessible after exec, typically
89 * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give
90 * up now (on the assumption that the interpreter will want to load
91 * this file).
92 */
93 if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
94 return -ENOENT;
95
96 /*
97 * OK, we've parsed out the interpreter name and
98 * (optional) argument.
99 * Splice in (1) the interpreter's name for argv[0]
100 * (2) (optional) argument to interpreter
101 * (3) filename of shell script (replace argv[0])
102 *
103 * This is done in reverse order, because of how the
104 * user environment and arguments are stored.
105 */
106 retval = remove_arg_zero(bprm);
107 if (retval)
108 return retval;
109 retval = copy_string_kernel(bprm->interp, bprm);
110 if (retval < 0)
111 return retval;
112 bprm->argc++;
113 *((char *)i_end) = '\0';
114 if (i_arg) {
115 *((char *)i_sep) = '\0';
116 retval = copy_string_kernel(i_arg, bprm);
117 if (retval < 0)
118 return retval;
119 bprm->argc++;
120 }
121 retval = copy_string_kernel(i_name, bprm);
122 if (retval)
123 return retval;
124 bprm->argc++;
125 retval = bprm_change_interp(i_name, bprm);
126 if (retval < 0)
127 return retval;
128
129 /*
130 * OK, now restart the process with the interpreter's dentry.
131 */
132 file = open_exec(i_name);
133 if (IS_ERR(file))
134 return PTR_ERR(file);
135
136 bprm->interpreter = file;
137 return 0;
138 }
139
140 static struct linux_binfmt script_format = {
141 .module = THIS_MODULE,
142 .load_binary = load_script,
143 };
144
145 static int __init init_script_binfmt(void)
146 {
147 register_binfmt(&script_format);
148 return 0;
149 }
150
151 static void __exit exit_script_binfmt(void)
152 {
153 unregister_binfmt(&script_format);
154 }
155
156 core_initcall(init_script_binfmt);
157 module_exit(exit_script_binfmt);
158 MODULE_DESCRIPTION("Kernel support for scripts starting with #!");
159 MODULE_LICENSE("GPL");
160
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