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Subject: Re: [PATCH] spi: bcm2835: Fix buffer overflow with CS able to go
 beyond limit.
To:     Joe Burmeister <joe.burmeister@devtank.co.uk>,
        Mark Brown <broonie@kernel.org>, Ray Jui <rjui@broadcom.com>,
        Scott Branden <sbranden@broadcom.com>,
        bcm-kernel-feedback-list@broadcom.com,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        linux-spi@vger.kernel.org, linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20210420083402.6950-1-joe.burmeister@devtank.co.uk>
From:   Florian Fainelli <f.fainelli@gmail.com>
Message-ID: <c087ba2c-7839-02d1-a522-b104d8ffb8d2@gmail.com>
Date:   Thu, 22 Apr 2021 09:50:47 -0700
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On 4/20/2021 1:34 AM, Joe Burmeister wrote:
> It was previoulsy possible to have a device tree with more chips than
> the driver supports and go off the end of CS arrays.

Do you mind walking me through the code how that could have happened? We
have spi_register_controller() call of_spi_get_gpio_numbers() which has
the following:

ctlr->num_chipselect = max_t(int, nb, ctlr->num_chipselect);

such that what the controller has is the maximum between the number of
'cs-gpios' properties parsed and what was already populated in
ctrl->num_chipselect during bcm2835_spi_probe(), which for this driver
is BCM2835_SPI_NUM_CS (3).

> 
> This patches inforces CS limit but sets that limit to the max of the
> default limit and what is in the device tree when driver is loaded.
> 
> Signed-off-by: Joe Burmeister <joe.burmeister@devtank.co.uk>

You have changed many more things that just enforcing a limit on
BCM2835_SPI_NUM_CS you have now made all chip-select related data
structuresd dynamically allocated and you have changed a number of
prints to use the shorthand "dev" instead of &pdev->dev.
-- 
Florian