linux/fs/binfmt_script.c
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   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_LICENSE("GPL");
 159
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