Bad Address Error from copy_to_user

Question

I am trying to copy a custom structure from kernel space to user space. inside user space, errno returns a "bad address". What is the common cause of an invalid address error?

if(copy_to_user(info, &kernel_info, sizeof(struct prinfo)))

Answer 1

A Bad Address error means that the address you entered is not valid. In case you are already higher, I would suggest that this is because you are passing a copy infoinstead of a pointer to the memory location info.

Looking at documents is copy_to_userdefined as

copy_to_user(void __user * to, const void * from, unsigned long n);

So, if your variable is infonot specified, I would update your code:

if(copy_to_user(&info, &kernel_info, sizeof(struct prinfo)) ) {
    //some stuff here i guess
}

Answer 2

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Answer 3

I had the same problem when writing a small char driver. All I did wrong is the copy_to_user function returns a non-zero value on failure, so you need to do this.

if(copy_to_user(void *userbuf, void *kernelbuf, long len))
    return -EFAULT;

// Continue with code..