// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/binfmt_script.c
 *
 *  Copyright (C) 1996  Martin von Löwis
 *  original #!-checking implemented by tytso.
 */

#include <linux/module.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/binfmts.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/err.h>
#include <linux/fs.h>

static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
static inline const char *next_non_spacetab(const char *first, const char *last)
{
        for (; first <= last; first++)
                if (!spacetab(*first))
                        return first;
        return NULL;
}
static inline const char *next_terminator(const char *first, const char *last)
{
        for (; first <= last; first++)
                if (spacetab(*first) || !*first)
                        return first;
        return NULL;
}

static int load_script(struct linux_binprm *bprm)
{
        const char *i_name, *i_sep, *i_arg, *i_end, *buf_end;
        struct file *file;
        int retval;

        /* Not ours to exec if we don't start with "#!". */
        if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
                return -ENOEXEC;

        /*
         * This section handles parsing the #! line into separate
         * interpreter path and argument strings. We must be careful
         * because bprm->buf is not yet guaranteed to be NUL-terminated
         * (though the buffer will have trailing NUL padding when the
         * file size was smaller than the buffer size).
         *
         * We do not want to exec a truncated interpreter path, so either
         * we find a newline (which indicates nothing is truncated), or
         * we find a space/tab/NUL after the interpreter path (which
         * itself may be preceded by spaces/tabs). Truncating the
         * arguments is fine: the interpreter can re-read the script to
         * parse them on its own.
         */
        buf_end = bprm->buf + sizeof(bprm->buf) - 1;
        i_end = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
        if (!i_end) {
                i_end = next_non_spacetab(bprm->buf + 2, buf_end);
                if (!i_end)
                        return -ENOEXEC; /* Entire buf is spaces/tabs */
                /*
                 * If there is no later space/tab/NUL we must assume the
                 * interpreter path is truncated.
                 */
                if (!next_terminator(i_end, buf_end))
                        return -ENOEXEC;
                i_end = buf_end;
        }
        /* Trim any trailing spaces/tabs from i_end */
        while (spacetab(i_end[-1]))
                i_end--;

        /* Skip over leading spaces/tabs */
        i_name = next_non_spacetab(bprm->buf+2, i_end);
        if (!i_name || (i_name == i_end))
                return -ENOEXEC; /* No interpreter name found */

        /* Is there an optional argument? */
        i_arg = NULL;
        i_sep = next_terminator(i_name, i_end);
        if (i_sep && (*i_sep != '\0'))
                i_arg = next_non_spacetab(i_sep, i_end);

        /*
         * If the script filename will be inaccessible after exec, typically
         * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give
         * up now (on the assumption that the interpreter will want to load
         * this file).
         */
        if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
                return -ENOENT;

        /*
         * OK, we've parsed out the interpreter name and
         * (optional) argument.
         * Splice in (1) the interpreter's name for argv[0]
         *           (2) (optional) argument to interpreter
         *           (3) filename of shell script (replace argv[0])
         *
         * This is done in reverse order, because of how the
         * user environment and arguments are stored.
         */
        retval = remove_arg_zero(bprm);
        if (retval)
                return retval;
        retval = copy_string_kernel(bprm->interp, bprm);
        if (retval < 0)
                return retval;
        bprm->argc++;
        *((char *)i_end) = '\0';
        if (i_arg) {
                *((char *)i_sep) = '\0';
                retval = copy_string_kernel(i_arg, bprm);
                if (retval < 0)
                        return retval;
                bprm->argc++;
        }
        retval = copy_string_kernel(i_name, bprm);
        if (retval)
                return retval;
        bprm->argc++;
        retval = bprm_change_interp(i_name, bprm);
        if (retval < 0)
                return retval;

        /*
         * OK, now restart the process with the interpreter's dentry.
         */
        file = open_exec(i_name);
        if (IS_ERR(file))
                return PTR_ERR(file);

        bprm->interpreter = file;
        return 0;
}

static struct linux_binfmt script_format = {
        .module         = THIS_MODULE,
        .load_binary    = load_script,
};

static int __init init_script_binfmt(void)
{
        register_binfmt(&script_format);
        return 0;
}

static void __exit exit_script_binfmt(void)
{
        unregister_binfmt(&script_format);
}

core_initcall(init_script_binfmt);
module_exit(exit_script_binfmt);
MODULE_DESCRIPTION("Kernel support for scripts starting with #!");
MODULE_LICENSE("GPL");