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Date: Wed, 26 Aug 2026 12:34:16 -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: <ao8xqMXoCfj4AWUw@kbusch-mbp>
References: <1819786.1787768317@warthog.procyon.org.uk>
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In-Reply-To: <1819786.1787768317@warthog.procyon.org.uk>

On Wed, Aug 26, 2026 at 07:18:37PM +0100, David Howells wrote:
> @@ -1921,15 +1921,19 @@ ssize_t iov_iter_extract_bvecs(struct iov_iter *iter, struct bio_vec *bv,
>  		unsigned short max_vecs, unsigned mem_align_mask,
>  		iov_iter_extraction_t extraction_flags)
>  {
> -	unsigned long start = (unsigned long)iter_iov_addr(iter);
>  	unsigned short entries_left = max_vecs - *nr_vecs;
>  	unsigned short nr_pages, i = 0;
>  	size_t left, offset, len;
>  	struct page **pages;
>  	ssize_t size;
>  
> -	if ((start | iter_iov_len(iter)) & mem_align_mask)
> +	if (iov_iter_alignment(iter) & mem_align_mask) {
> +		pr_warn("%u %zx %x\n",
> +			iter->iter_type,
> +			iov_iter_alignment(iter),
> +			mem_align_mask);
>  		return -EINVAL;
> +	}

iov_iter_alignment loops over all the vectors when we only need to
examine the current one here.