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 char *next_non_spacetab(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 char *next_terminator(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_arg, *i_name;
  37         char *cp, *buf_end;
  38         struct file *file;
  39         int retval;
  40
  41         /* Not ours to exec if we don't start with "#!". */
  42         if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
  43                 return -ENOEXEC;
  44
  45         /*
  46          * If the script filename will be inaccessible after exec, typically
  47          * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give
  48          * up now (on the assumption that the interpreter will want to load
  49          * this file).
  50          */
  51         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
  52                 return -ENOENT;
  53
  54         /* Release since we are not mapping a binary into memory. */
  55         allow_write_access(bprm->file);
  56         fput(bprm->file);
  57         bprm->file = NULL;
  58
  59         /*
  60          * This section handles parsing the #! line into separate
  61          * interpreter path and argument strings. We must be careful
  62          * because bprm->buf is not yet guaranteed to be NUL-terminated
  63          * (though the buffer will have trailing NUL padding when the
  64          * file size was smaller than the buffer size).
  65          *
  66          * We do not want to exec a truncated interpreter path, so either
  67          * we find a newline (which indicates nothing is truncated), or
  68          * we find a space/tab/NUL after the interpreter path (which
  69          * itself may be preceded by spaces/tabs). Truncating the
  70          * arguments is fine: the interpreter can re-read the script to
  71          * parse them on its own.
  72          */
  73         buf_end = bprm->buf + sizeof(bprm->buf) - 1;
  74         cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
  75         if (!cp) {
  76                 cp = next_non_spacetab(bprm->buf + 2, buf_end);
  77                 if (!cp)
  78                         return -ENOEXEC; /* Entire buf is spaces/tabs */
  79                 /*
  80                  * If there is no later space/tab/NUL we must assume the
  81                  * interpreter path is truncated.
  82                  */
  83                 if (!next_terminator(cp, buf_end))
  84                         return -ENOEXEC;
  85                 cp = buf_end;
  86         }
  87         /* NUL-terminate the buffer and any trailing spaces/tabs. */
  88         *cp = '\0';
  89         while (cp > bprm->buf) {
  90                 cp--;
  91                 if ((*cp == ' ') || (*cp == '\t'))
  92                         *cp = '\0';
  93                 else
  94                         break;
  95         }
  96         for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
  97         if (*cp == '\0')
  98                 return -ENOEXEC; /* No interpreter name found */
  99         i_name = cp;
 100         i_arg = NULL;
 101         for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++)
 102                 /* nothing */ ;
 103         while ((*cp == ' ') || (*cp == '\t'))
 104                 *cp++ = '\0';
 105         if (*cp)
 106                 i_arg = cp;
 107         /*
 108          * OK, we've parsed out the interpreter name and
 109          * (optional) argument.
 110          * Splice in (1) the interpreter's name for argv[0]
 111          *           (2) (optional) argument to interpreter
 112          *           (3) filename of shell script (replace argv[0])
 113          *
 114          * This is done in reverse order, because of how the
 115          * user environment and arguments are stored.
 116          */
 117         retval = remove_arg_zero(bprm);
 118         if (retval)
 119                 return retval;
 120         retval = copy_strings_kernel(1, &bprm->interp, bprm);
 121         if (retval < 0)
 122                 return retval;
 123         bprm->argc++;
 124         if (i_arg) {
 125                 retval = copy_strings_kernel(1, &i_arg, bprm);
 126                 if (retval < 0)
 127                         return retval;
 128                 bprm->argc++;
 129         }
 130         retval = copy_strings_kernel(1, &i_name, bprm);
 131         if (retval)
 132                 return retval;
 133         bprm->argc++;
 134         retval = bprm_change_interp(i_name, bprm);
 135         if (retval < 0)
 136                 return retval;
 137
 138         /*
 139          * OK, now restart the process with the interpreter's dentry.
 140          */
 141         file = open_exec(i_name);
 142         if (IS_ERR(file))
 143                 return PTR_ERR(file);
 144
 145         bprm->file = file;
 146         retval = prepare_binprm(bprm);
 147         if (retval < 0)
 148                 return retval;
 149         return search_binary_handler(bprm);
 150 }
 151
 152 static struct linux_binfmt script_format = {
 153         .module         = THIS_MODULE,
 154         .load_binary    = load_script,
 155 };
 156
 157 static int __init init_script_binfmt(void)
 158 {
 159         register_binfmt(&script_format);
 160         return 0;
 161 }
 162
 163 static void __exit exit_script_binfmt(void)
 164 {
 165         unregister_binfmt(&script_format);
 166 }
 167
 168 core_initcall(init_script_binfmt);
 169 module_exit(exit_script_binfmt);
 170 MODULE_LICENSE("GPL");