LXR linux/fs/binfmt

   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 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}
  26static 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
  34static 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
 152static struct linux_binfmt script_format = {
 153        .module         = THIS_MODULE,
 154        .load_binary    = load_script,
 155};
 156
 157static int __init init_script_binfmt(void)
 158{
 159        register_binfmt(&script_format);
 160        return 0;
 161}
 162
 163static void __exit exit_script_binfmt(void)
 164{
 165        unregister_binfmt(&script_format);
 166}
 167
 168core_initcall(init_script_binfmt);
 169module_exit(exit_script_binfmt);
 170MODULE_LICENSE("GPL");
 171