binfmt_script.c

  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
 18static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
 19static 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}
 26static 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
 34static 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
140static struct linux_binfmt script_format = {
141	.module		= THIS_MODULE,
142	.load_binary	= load_script,
143};
144
145static int __init init_script_binfmt(void)
146{
147	register_binfmt(&script_format);
148	return 0;
149}
150
151static void __exit exit_script_binfmt(void)
152{
153	unregister_binfmt(&script_format);
154}
155
156core_initcall(init_script_binfmt);
157module_exit(exit_script_binfmt);
158MODULE_DESCRIPTION("Kernel support for scripts starting with #!");
159MODULE_LICENSE("GPL");