iov_iter: Fix missing alloc fail check in iov_iter_extract_bvec_pages()

Fix iov_iter_extract_bvec_pages() to check if want_pages_array() fails and,
if so, return -ENOMEM appropriately.

Fixes: e4e535bff2 ("iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages")
Link: https://sashiko.dev/#/patchset/20260608145432.681865-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260625140640.3116900-7-dhowells@redhat.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
cc: Ming Lei <ming.lei@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: Christoph Hellwig <hch@infradead.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

lib/iov_iter.c

@@ -1637,6 +1637,8 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
 	bi.bi_bvec_done = skip;
 
 	maxpages = want_pages_array(pages, maxsize, skip, maxpages);
+	if (!maxpages)
+		return -ENOMEM;
 
 	while (bi.bi_size && bi.bi_idx < i->nr_segs) {
 		struct bio_vec bv = bvec_iter_bvec(i->bvec, bi);