lkml.org 
[lkml]   [2001]   [Nov]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: null pointer questions
Brian Gerst wrote:
>
> Ken Ashcraft wrote:
> >
> > > > 2. What happens if I pass a null pointer as the destination parameter
> > > > to copy_from_user? Does copy_from_user handle it safely or will the
> > > > kernel seg fault?
> > >
> > > The kernel won't crash, but it might fail (depending on whether 0 is a
> > > valid user space address or not).
> >
> > Why does it matter if 0 is a valid user space or not? If I make the call
> >
> > copy_from_user(0, user_ptr, 4);
> >
> > the null pointer is the kernel address, not the user address. Can you
> > clarify please?
>
> copy_from_user uses the string move instruction on the x86, so the
> exception code would assume the source faulted not the dest. It would
> return -EFAULT instead of causing an oops.

Err, would return non-zero instead of -EFAULT.

--

Brian Gerst
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:12    [from the cache]
©2003-2011 Jasper Spaans