linux-kernel - Re: [PATCH] spi: bcm2835: Fix buffer overflow with CS able to go beyond limit.

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Date:   Thu, 22 Apr 2021 09:50:47 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Joe Burmeister <joe.burmeister@...tank.co.uk>,
        Mark Brown <broonie@...nel.org>, Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        linux-spi@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: bcm2835: Fix buffer overflow with CS able to go
 beyond limit.



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@...tank.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