On Thu, Nov 06, 2014 at 04:28:18PM +0800, Herbert Xu wrote:
> + if (copy_to_iter(skb->data + offset, copy, to))
> + goto fault;
Sorry, no - copy_to_iter() returns the number of bytes copied, not 0 or -EFAULT.
> + vaddr = kmap(page);
> + err = copy_to_iter(vaddr + frag->page_offset +
> + offset - start, copy, to);
> + kunmap(page);
> + if (err)
> + goto fault;
And that one should be
copied = copy_page_to_iter(page, frag->page_offset +
offset - start, copy, to);
if (copied != copy)
goto fault;
Don't bother with kmap(), vaddr and all that shite. The primitive is
copy_page_to_iter(page, offset_in_page, nbytes, iter)
it does all needed kmap itself and it's smart enough to use kmap_atomic
when it can get away with that. Similar for copy_page_from_iter().
Both of those (as well as copy_{to,from}_iter()) advance iov_iter and return
the number of bytes actually copied. So the check for EFAULT is "it has copied
less than you've asked it to copy *and* you haven't run out that iov_iter".
The second part is guaranteed to be true in this case - your code makes sure
that 'copy' is no more than the space left in iterator.
In general, this check would be spelled
if (copied != copy && iov_iter_count(to))
goto fault;
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