fs/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
  18 static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
  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 }
  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
  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
 145 static int __init init_script_binfmt(void)
 146 {
 147         register_binfmt(&script_format);
 148         return 0;
 149 }
 150
 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_LICENSE("GPL");