请谁回答下：copy_to_user()前是否还有必要调用access_ok()检验一下？

Question

请熟悉驱动的人回答下：copy_to_user(buf, ...)前是否还有必要调用access_ok(VERIFY_WTITE, ...)检验一下？

Answer 1

原帖由 vdigital 于 2008-8-4 10:49 发表
请熟悉驱动的人回答下：copy_to_user(buf, ...)前是否还有必要调用access_ok(VERIFY_WTITE, ...)检验一下？

如果你确保这样操作没问题，那就没必要了。搞明白access_ok(VERIFY_WTITE, ...)是干什么的。

Answer 2

没有必要。。。copy_to_user自身会检查用户空间提供的地址有效性。。。

Answer 3

/**
* copy_from_user: - Copy a block of data from user space.
* @to:   Destination address, in kernel space.
* @from: Source address, in user space.
* @n:    Number of bytes to copy.
*
* Context: User context only.  This function may sleep.
*
* Copy data from user space to kernel space.
*
* Returns number of bytes that could not be copied.
* On success, this will be zero.
*
* If some data could not be copied, this function will pad the copied
* data to the requested size using zero bytes.
*/
unsigned long
copy_from_user(void *to, const void __user *from, unsigned long n)
{
        BUG_ON((long) n < 0);
        if (access_ok(VERIFY_READ, from, n))
                n = __copy_from_user(to, from, n);
        else
                memset(to, 0, n);
        return n;
}
这个是X86的实现。由此可见，确实不需要access_ok了