fs/binfmt_script.c

   1 /*
   2  *  linux/fs/binfmt_script.c
   3  *
   4  *  Copyright (C) 1996  Martin von Löwis
   5  *  original #!-checking implemented by tytso.
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/string.h>
  10 #include <linux/stat.h>
  11 #include <linux/binfmts.h>
  12 #include <linux/init.h>
  13 #include <linux/file.h>
  14 #include <linux/err.h>
  15 #include <linux/fs.h>
  16
  17 static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
  18 static inline char *next_non_spacetab(char *first, const char *last)
  19 {
  20         for (; first <= last; first++)
  21                 if (!spacetab(*first))
  22                         return first;
  23         return NULL;
  24 }
  25 static inline char *next_terminator(char *first, const char *last)
  26 {
  27         for (; first <= last; first++)
  28                 if (spacetab(*first) || !*first)
  29                         return first;
  30         return NULL;
  31 }
  32
  33 static int load_script(struct linux_binprm *bprm)
  34 {
  35         const char *i_arg, *i_name;
  36         char *cp, *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          * If the script filename will be inaccessible after exec, typically
  46          * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give
  47          * up now (on the assumption that the interpreter will want to load
  48          * this file).
  49          */
  50         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
  51                 return -ENOENT;
  52
  53         /* Release since we are not mapping a binary into memory. */
  54         allow_write_access(bprm->file);
  55         fput(bprm->file);
  56         bprm->file = NULL;
  57
  58         /*
  59          * This section handles parsing the #! line into separate
  60          * interpreter path and argument strings. We must be careful
  61          * because bprm->buf is not yet guaranteed to be NUL-terminated
  62          * (though the buffer will have trailing NUL padding when the
  63          * file size was smaller than the buffer size).
  64          *
  65          * We do not want to exec a truncated interpreter path, so either
  66          * we find a newline (which indicates nothing is truncated), or
  67          * we find a space/tab/NUL after the interpreter path (which
  68          * itself may be preceded by spaces/tabs). Truncating the
  69          * arguments is fine: the interpreter can re-read the script to
  70          * parse them on its own.
  71          */
  72         buf_end = bprm->buf + sizeof(bprm->buf) - 1;
  73         cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
  74         if (!cp) {
  75                 cp = next_non_spacetab(bprm->buf + 2, buf_end);
  76                 if (!cp)
  77                         return -ENOEXEC; /* Entire buf is spaces/tabs */
  78                 /*
  79                  * If there is no later space/tab/NUL we must assume the
  80                  * interpreter path is truncated.
  81                  */
  82                 if (!next_terminator(cp, buf_end))
  83                         return -ENOEXEC;
  84                 cp = buf_end;
  85         }
  86         /* NUL-terminate the buffer and any trailing spaces/tabs. */
  87         *cp = '\0';
  88         while (cp > bprm->buf) {
  89                 cp--;
  90                 if ((*cp == ' ') || (*cp == '\t'))
  91                         *cp = '\0';
  92                 else
  93                         break;
  94         }
  95         for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
  96         if (*cp == '\0')
  97                 return -ENOEXEC; /* No interpreter name found */
  98         i_name = cp;
  99         i_arg = NULL;
 100         for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++)
 101                 /* nothing */ ;
 102         while ((*cp == ' ') || (*cp == '\t'))
 103                 *cp++ = '\0';
 104         if (*cp)
 105                 i_arg = cp;
 106         /*
 107          * OK, we've parsed out the interpreter name and
 108          * (optional) argument.
 109          * Splice in (1) the interpreter's name for argv[0]
 110          *           (2) (optional) argument to interpreter
 111          *           (3) filename of shell script (replace argv[0])
 112          *
 113          * This is done in reverse order, because of how the
 114          * user environment and arguments are stored.
 115          */
 116         retval = remove_arg_zero(bprm);
 117         if (retval)
 118                 return retval;
 119         retval = copy_strings_kernel(1, &bprm->interp, bprm);
 120         if (retval < 0)
 121                 return retval;
 122         bprm->argc++;
 123         if (i_arg) {
 124                 retval = copy_strings_kernel(1, &i_arg, bprm);
 125                 if (retval < 0)
 126                         return retval;
 127                 bprm->argc++;
 128         }
 129         retval = copy_strings_kernel(1, &i_name, bprm);
 130         if (retval)
 131                 return retval;
 132         bprm->argc++;
 133         retval = bprm_change_interp(i_name, bprm);
 134         if (retval < 0)
 135                 return retval;
 136
 137         /*
 138          * OK, now restart the process with the interpreter's dentry.
 139          */
 140         file = open_exec(i_name);
 141         if (IS_ERR(file))
 142                 return PTR_ERR(file);
 143
 144         bprm->file = file;
 145         retval = prepare_binprm(bprm);
 146         if (retval < 0)
 147                 return retval;
 148         return search_binary_handler(bprm);
 149 }
 150
 151 static struct linux_binfmt script_format = {
 152         .module         = THIS_MODULE,
 153         .load_binary    = load_script,
 154 };
 155
 156 static int __init init_script_binfmt(void)
 157 {
 158         register_binfmt(&script_format);
 159         return 0;
 160 }
 161
 162 static void __exit exit_script_binfmt(void)
 163 {
 164         unregister_binfmt(&script_format);
 165 }
 166
 167 core_initcall(init_script_binfmt);
 168 module_exit(exit_script_binfmt);
 169 MODULE_LICENSE("GPL");