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uaccess.c

/* uaccess.c: userspace access functions
 *
 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <asm/uaccess.h>

/*****************************************************************************/
/*
 * copy a null terminated string from userspace
 */
long strncpy_from_user(char *dst, const char __user *src, long count)
{
      unsigned long max;
      char *p, ch;
      long err = -EFAULT;

      BUG_ON(count < 0);

      p = dst;

#ifndef CONFIG_MMU
      if ((unsigned long) src < memory_start)
            goto error;
#endif

      if ((unsigned long) src >= get_addr_limit())
            goto error;

      max = get_addr_limit() - (unsigned long) src;
      if ((unsigned long) count > max) {
            memset(dst + max, 0, count - max);
            count = max;
      }

      err = 0;
      for (; count > 0; count--, p++, src++) {
            __get_user_asm(err, ch, src, "ub", "=r");
            if (err < 0)
                  goto error;
            if (!ch)
                  break;
            *p = ch;
      }

      err = p - dst; /* return length excluding NUL */

 error:
      if (count > 0)
            memset(p, 0, count); /* clear remainder of buffer [security] */

      return err;

} /* end strncpy_from_user() */

EXPORT_SYMBOL(strncpy_from_user);

/*****************************************************************************/
/*
 * Return the size of a string (including the ending 0)
 *
 * Return 0 on exception, a value greater than N if too long
 */
long strnlen_user(const char __user *src, long count)
{
      const char __user *p;
      long err = 0;
      char ch;

      BUG_ON(count < 0);

#ifndef CONFIG_MMU
      if ((unsigned long) src < memory_start)
            return 0;
#endif

      if ((unsigned long) src >= get_addr_limit())
            return 0;

      for (p = src; count > 0; count--, p++) {
            __get_user_asm(err, ch, p, "ub", "=r");
            if (err < 0)
                  return 0;
            if (!ch)
                  break;
      }

      return p - src + 1; /* return length including NUL */

} /* end strnlen_user() */

EXPORT_SYMBOL(strnlen_user);

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