xref: /linux/fs/binfmt_script.c (revision a1ff5a7d78a036d6c2178ee5acd6ba4946243800)
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 
spacetab(char c)18 static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
next_non_spacetab(const char * first,const char * last)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 }
next_terminator(const char * first,const char * last)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 
load_script(struct linux_binprm * bprm)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 
init_script_binfmt(void)145 static int __init init_script_binfmt(void)
146 {
147 	register_binfmt(&script_format);
148 	return 0;
149 }
150 
exit_script_binfmt(void)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