the-tree/fs/binfmt_script.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  linux/fs/binfmt_script.c
0004  *
0005  *  Copyright (C) 1996  Martin von Löwis
0006  *  original #!-checking implemented by tytso.
0007  */
0008
0009 #include <linux/module.h>
0010 #include <linux/string.h>
0011 #include <linux/stat.h>
0012 #include <linux/binfmts.h>
0013 #include <linux/init.h>
0014 #include <linux/file.h>
0015 #include <linux/err.h>
0016 #include <linux/fs.h>
0017
0018 static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
0019 static inline const char *next_non_spacetab(const char *first, const char *last)
0020 {
0021     for (; first <= last; first++)
0022         if (!spacetab(*first))
0023             return first;
0024     return NULL;
0025 }
0026 static inline const char *next_terminator(const char *first, const char *last)
0027 {
0028     for (; first <= last; first++)
0029         if (spacetab(*first) || !*first)
0030             return first;
0031     return NULL;
0032 }
0033
0034 static int load_script(struct linux_binprm *bprm)
0035 {
0036     const char *i_name, *i_sep, *i_arg, *i_end, *buf_end;
0037     struct file *file;
0038     int retval;
0039
0040     /* Not ours to exec if we don't start with "#!". */
0041     if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
0042         return -ENOEXEC;
0043
0044     /*
0045      * This section handles parsing the #! line into separate
0046      * interpreter path and argument strings. We must be careful
0047      * because bprm->buf is not yet guaranteed to be NUL-terminated
0048      * (though the buffer will have trailing NUL padding when the
0049      * file size was smaller than the buffer size).
0050      *
0051      * We do not want to exec a truncated interpreter path, so either
0052      * we find a newline (which indicates nothing is truncated), or
0053      * we find a space/tab/NUL after the interpreter path (which
0054      * itself may be preceded by spaces/tabs). Truncating the
0055      * arguments is fine: the interpreter can re-read the script to
0056      * parse them on its own.
0057      */
0058     buf_end = bprm->buf + sizeof(bprm->buf) - 1;
0059     i_end = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
0060     if (!i_end) {
0061         i_end = next_non_spacetab(bprm->buf + 2, buf_end);
0062         if (!i_end)
0063             return -ENOEXEC; /* Entire buf is spaces/tabs */
0064         /*
0065          * If there is no later space/tab/NUL we must assume the
0066          * interpreter path is truncated.
0067          */
0068         if (!next_terminator(i_end, buf_end))
0069             return -ENOEXEC;
0070         i_end = buf_end;
0071     }
0072     /* Trim any trailing spaces/tabs from i_end */
0073     while (spacetab(i_end[-1]))
0074         i_end--;
0075
0076     /* Skip over leading spaces/tabs */
0077     i_name = next_non_spacetab(bprm->buf+2, i_end);
0078     if (!i_name || (i_name == i_end))
0079         return -ENOEXEC; /* No interpreter name found */
0080
0081     /* Is there an optional argument? */
0082     i_arg = NULL;
0083     i_sep = next_terminator(i_name, i_end);
0084     if (i_sep && (*i_sep != '\0'))
0085         i_arg = next_non_spacetab(i_sep, i_end);
0086
0087     /*
0088      * If the script filename will be inaccessible after exec, typically
0089      * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give
0090      * up now (on the assumption that the interpreter will want to load
0091      * this file).
0092      */
0093     if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
0094         return -ENOENT;
0095
0096     /*
0097      * OK, we've parsed out the interpreter name and
0098      * (optional) argument.
0099      * Splice in (1) the interpreter's name for argv[0]
0100      *           (2) (optional) argument to interpreter
0101      *           (3) filename of shell script (replace argv[0])
0102      *
0103      * This is done in reverse order, because of how the
0104      * user environment and arguments are stored.
0105      */
0106     retval = remove_arg_zero(bprm);
0107     if (retval)
0108         return retval;
0109     retval = copy_string_kernel(bprm->interp, bprm);
0110     if (retval < 0)
0111         return retval;
0112     bprm->argc++;
0113     *((char *)i_end) = '\0';
0114     if (i_arg) {
0115         *((char *)i_sep) = '\0';
0116         retval = copy_string_kernel(i_arg, bprm);
0117         if (retval < 0)
0118             return retval;
0119         bprm->argc++;
0120     }
0121     retval = copy_string_kernel(i_name, bprm);
0122     if (retval)
0123         return retval;
0124     bprm->argc++;
0125     retval = bprm_change_interp(i_name, bprm);
0126     if (retval < 0)
0127         return retval;
0128
0129     /*
0130      * OK, now restart the process with the interpreter's dentry.
0131      */
0132     file = open_exec(i_name);
0133     if (IS_ERR(file))
0134         return PTR_ERR(file);
0135
0136     bprm->interpreter = file;
0137     return 0;
0138 }
0139
0140 static struct linux_binfmt script_format = {
0141     .module     = THIS_MODULE,
0142     .load_binary    = load_script,
0143 };
0144
0145 static int __init init_script_binfmt(void)
0146 {
0147     register_binfmt(&script_format);
0148     return 0;
0149 }
0150
0151 static void __exit exit_script_binfmt(void)
0152 {
0153     unregister_binfmt(&script_format);
0154 }
0155
0156 core_initcall(init_script_binfmt);
0157 module_exit(exit_script_binfmt);
0158 MODULE_LICENSE("GPL");