On Thu, Nov 06, 2014 at 05:30:12PM +0000, Al Viro wrote:
> 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;
Thanks, I'll redo the patches.
--
Email: Herbert Xu <herb...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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