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Date: Thu, 18 Jun 2026 07:51:01 -0600
From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <kbusch@meta.com>, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, dm-devel@lists.linux.dev,
	axboe@kernel.dk, brauner@kernel.org, djwong@kernel.org,
	viro@zeniv.linux.org.uk, stable@vger.kernel.org
Subject: Re: [PATCH 1/1] block: validate user space vectors during extraction
Message-ID: <ajP3xZOlaMVz3VUr@kbusch-mbp>
References: <20260617233235.1016063-1-kbusch@meta.com>
 <20260617233235.1016063-2-kbusch@meta.com>
 <20260618102627.GA23200@lst.de>
 <ajPv7yOoYsR5O6kf@kbusch-mbp>
 <20260618134346.GA2752@lst.de>
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In-Reply-To: <20260618134346.GA2752@lst.de>

On Thu, Jun 18, 2026 at 03:43:46PM +0200, Christoph Hellwig wrote:
> On Thu, Jun 18, 2026 at 07:17:35AM -0600, Keith Busch wrote:
> > > >  	if (iov_iter_is_bvec(iter)) {
> > > >  		bio_iov_bvec_set(bio, iter);
> > > > +
> > > > +		if (mp_bvec_iter_offset(bio->bi_io_vec, bio->bi_iter) &
> > > > +							vec_align_mask)
> > > > +			return -EINVAL;
> > > 
> > > Can you add a comment here?  Especially as the bvec iter doesn't actually
> > > require all individual bvecs to be aligned and I'm not entirely sure this
> > > handles all case - writing down the rules might help a bit with that.
> > 
> > The rationale is that the only iter_bvec users come from io_uring
> > registered buffers, which are virtually contiguous.
> 
> There's plenty of iov_iter_bdev users, and even without poking deep I
> know that two directly passed on bvecs from block-layer generated bios to
> the underlying file system's direct I/O code: loop and zloop.

Oh, I meant only users that go through this direct-io path, but you're
right, I was wrong about that too. The nvme target file backend can also
get here in addition to what you pointed out.
 
> So we need rules on what can be passed, and preferably some way to
> enforce that at least for debug builds.

Yeah.