linux-kernel - Re: [PATCH v2] nvmem: eeprom: at25: fix FRAM byte

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Date:   Mon, 8 Nov 2021 19:27:07 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Ralph Siemsen <ralph.siemsen@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>, gregkh <gregkh@...uxfoundation.org>,
        jiri.prchal@...ignal.cz, Mark Brown <broonie@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] nvmem: eeprom: at25: fix FRAM byte_len

On Mon, Nov 8, 2021 at 7:16 PM Ralph Siemsen <ralph.siemsen@...aro.org> wrote:
>
> Commit fd307a4ad332 ("nvmem: prepare basics for FRAM support") added
> support for FRAM devices such as the Cypress FM25V. During testing, it
> was found that the FRAM detects properly, however reads and writes fail.
> Upon further investigation, two problem were found in at25_probe() routine.
>
> 1) In the case of an FRAM device without platform data, eg.
>        fram == true && spi->dev.platform_data == NULL
> the stack local variable "struct spi_eeprom chip" is not initialized
> fully, prior to being copied into at25->chip. The chip.flags field in
> particular can cause problems.
>
> 2) The byte_len of FRAM is computed from its ID register, and is stored
> into the stack local "struct spi_eeprom chip" structure. This happens
> after the same structure has been copied into at25->chip. As a result,
> at25->chip.byte_len does not contain the correct length of the device.
> In turn this can cause checks at beginning of at25_ee_read() to fail
> (or equally, it could allow reads beyond the end of the device length).
>
> Fix both of these issues by eliminating the on-stack struct spi_eeprom.
> Instead use the one inside at25_data structure, which starts of zeroed.
>
> Fixes: fd307a4ad332 ("nvmem: prepare basics for FRAM support")
> Signed-off-by: Ralph Siemsen <ralph.siemsen@...aro.org>

Reviewed-by: Arnd Bergmann <arnd@...db.de>