Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[asmadeus@codewreck.org]

David Howells wrote on Tue, Aug 12, 2025 at 10:34:17AM +0100:
> asmadeus@codewreck.org wrote:
> 
> > There should be a `if (slot == folioq_nr_slots(folioq)) break` check
> > somewhere as well? Or is the iov_iter guaranteed to always 1/ have some
> > data and 2/ either be big enough or have remaining data in a step?
> 
> We should handle both cases.  I think the other iteration functions
> will. iov_iter_extractg_folioq_pages(), for example, wraps it in a
> conditional:
> 
> 		if (offset < fsize) {
> 			part = umin(part, umin(maxsize - extracted, fsize - offset));
> 			i->count -= part;
> 			i->iov_offset += part;
> 			extracted += part;
> 
> 			p[nr++] = folio_page(folio, offset / PAGE_SIZE);
> 		}

That's not what I pointed out just now; it doesn't check either if there
is no slot left
For example, an iov_iter with nr_slots = 4, slot = 4, folioq->next =
NULL will happily trod on folioq->vec.folios[4] (folioq_folio(folioq,
slot)) which is invalid

-- 
Dominique Martinet | Asmadeus