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Date: Wed, 26 Aug 2026 14:02:43 -0600
From: Keith Busch <kbusch@kernel.org>
To: David Howells <dhowells@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Hannes Reinecke <hare@kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Paulo Alcantara <pc@manguebit.org>, netfs@lists.linux.dev,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] block: Fix start and length check added to
 iov_iter_extract_bvecs()
Message-ID: <ao9GY22aAvnZUye0@kbusch-mbp>
References: <ao8xqMXoCfj4AWUw@kbusch-mbp>
 <1819786.1787768317@warthog.procyon.org.uk>
 <1864928.1787773740@warthog.procyon.org.uk>
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In-Reply-To: <1864928.1787773740@warthog.procyon.org.uk>

On Wed, Aug 26, 2026 at 08:49:00PM +0100, David Howells wrote:
> Keith Busch <kbusch@kernel.org> wrote:
> 
> > iov_iter_alignment loops over all the vectors when we only need to
> > examine the current one here.
> 
> Actually, I don't think that's true.  iov_iter_extract_pages() is allowed to
> pull from multiple bio_vecs in an ITER_BVEC, for example - and if, say, the
> page in the second bio_vec is contiguous with the first, then
> iov_iter_extract_bvecs() will use it - so you still need to check bv_len on
> it.

I don't think we should be extracting bvecs for the ITER_BVEC type.
bio_iov_iter_get_pages() already doesn't. I'll look more into the
recently introduced bio_iov_iter_bounce_read() usage, as there may be an
optimization there.

But in general, yeah, it should be safe for any type. The proposal I
sent a bit ago will handle the ITER_BVEC as you've desribed.