If an spi-gpio was specified with num-chipselects = <0> in dts, kernel will crash:

Unable to handle kernel paging request at virtual address 32697073 pgd = (ptrval) [32697073] *pgd=00000000 Internal error: Oops: 5 [# 1] SMP ARM Modules linked in: CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.19.72 #0 Hardware name: Generic DT based system PC is at validate_desc+0x28/0x80 LR is at gpiod_direction_output+0x14/0x128 ... [<c0544db4>] (validate_desc) from [<c0545228>] (gpiod_direction_output+0x14/0x128) [<c0545228>] (gpiod_direction_output) from [<c05fa714>] (spi_gpio_setup+0x58/0x64) [<c05fa714>] (spi_gpio_setup) from [<c05f7258>] (spi_setup+0x12c/0x148) [<c05f7258>] (spi_setup) from [<c05f7330>] (spi_add_device+0xbc/0x12c) [<c05f7330>] (spi_add_device) from [<c05f7f74>] (spi_register_controller+0x838/0x924) [<c05f7f74>] (spi_register_controller) from [<c05fa494>] (spi_bitbang_start+0x108/0x120) [<c05fa494>] (spi_bitbang_start) from [<c05faa34>] (spi_gpio_probe+0x314/0x338) [<c05faa34>] (spi_gpio_probe) from [<c05a844c>] (platform_drv_probe+0x34/0x70)

The cause is spi_gpio_setup() did not check if the spi-gpio has chipselect pins before setting their direction and results in derefing an invalid pointer.

The bug is spotted in kernel 4.19.72 on OpenWrt, and does not occur in 4.14.

There is a similar fix upstream 249e2632dcd0509b8f8f296f5aabf4d48dfd6da8.

Cc: Linus Walleij linus.walleij@linaro.org Cc: stable@vger.kernel.org Signed-off-by: DENG Qingfang dqfext@gmail.com --- drivers/spi/spi-gpio.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c index 77838d8fd..3b7f0d077 100644 --- a/drivers/spi/spi-gpio.c +++ b/drivers/spi/spi-gpio.c @@ -242,10 +242,12 @@ static int spi_gpio_setup(struct spi_device *spi) * The CS GPIOs have already been * initialized from the descriptor lookup. */ - cs = spi_gpio->cs_gpios[spi->chip_select]; - if (!spi->controller_state && cs) - status = gpiod_direction_output(cs, - !(spi->mode & SPI_CS_HIGH)); + if (spi_gpio->has_cs) { + cs = spi_gpio->cs_gpios[spi->chip_select]; + if (!spi->controller_state && cs) + status = gpiod_direction_output(cs, + !(spi->mode & SPI_CS_HIGH)); + }

if (!status) status = spi_bitbang_setup(spi);