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Date:   Wed, 9 Nov 2022 13:58:29 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Daniel Golle <daniel@makrotopia.org>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
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        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Chaitanya Kulkarni <kch@nvidia.com>,
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        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
        linux-efi@vger.kernel.org
Subject: Re: [PATCH v4 2/5] block: add partition parser for U-Boot uImage.FIT
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On Tue, Nov 08, 2022 at 11:03:16PM +0000, Daniel Golle wrote:
> +	/* map first page */
> +	page = read_mapping_page(
> +		mapping, fit_start_sector >> (PAGE_SHIFT - SECTOR_SHIFT), NULL);
> +
> +	if (IS_ERR(page))
> +		return -EFAULT;
> +
> +	if (PageError(page))
> +		return -EFAULT;

Why are you checking for PageError?  You won't ever get a page with an
error back from read_mapping_page().  And you have the real error in
'page', so why return -EFAUlT, which would indicate a problem copying
from the user.  Also, this is a great place to use the new folio APIs
instead of the old page APIs.  So:

	folio = read_mapping_folio(mapping,
			fit_start_sector >> PAGE_SECTORS_SHIFT, NULL);
	if (IS_ERR(folio))
		return PTR_ERR(folio);

> +	init_fit = page_address(page);

	init_fit = folio_address(folio) +
			offset_in_folio(folio, fit_start_sector * SECTOR_SIZE);

> +	if (!init_fit) {
> +		put_page(page);
> +		return -EFAULT;
> +	}

page_address() or folio_address() can't ever return NULL, you should
just drop this nonsense check.

... actually, why can't you call read_part_sector() and avoid all of
this?