Re: AUDIT of 2.5.15 copy_to/from_user

[Rui Sousa]

On Sun, 19 May 2002, Alan Cox wrote:

> > copy_to/from_user() --> will return the number of bytes that were _not_ 
> > copied. If one does not care about partially successes just use:
> > 
> > if (copy_to/from_user())
> > 	return -EFAULT;
> 
> Yes
> 
> > __copy_to/from_user() --> the same as above, but can they actually return 
> > anything other than 0? My assembler is no good and I'm not able to see if
> 
> They do the same things, but don't do any initial range checks that might
> be done by access_ok before hand

On the emu10k1 driver we use access_ok(VERIFY_READ) once at the beginning
of the write() routine to check we can access the user buffer. After that 
we always use __copy_from_user() and we trust it not to fail. Is this 
correct, or not?

Basically, where in copy_from_user() is it determined the function cannot
copy the entire user buffer? Is it in access_ok() only or also in 
__constant_copy_user_zeroing()?

Rui