If the call to devm_spi_register_master() fails on probe of the GPIO SPI
driver, the spi_master struct is erroneously not freed:

After allocating the spi_master, its reference count is 1.  The driver
unconditionally decrements the reference count on unbind using a devm
action.  Before calling devm_spi_register_master(), the driver
unconditionally increments the reference count because on success,
that function will decrement the reference count on unbind.  However on
failure, devm_spi_register_master() does *not* decrement the reference
count, so the spi_master is leaked.

The issue was introduced by commits 8b797490 ("spi: gpio: Make sure
spi_master_put() is called in every error path") and 79567c1a ("spi:
gpio: Use devm_spi_register_master()"), which sought to plug leaks
introduced by 9b00bc7b ("spi: spi-gpio: Rewrite to use GPIO
descriptors") but missed this remaining leak.

The situation was later aggravated by commit d3b0ffa1 ("spi: gpio:
prevent memory leak in spi_gpio_probe"), which introduced a
use-after-free because it releases a reference on the spi_master if
devm_add_action_or_reset() fails even though the function already
does that.

Fix by switching over to the new devm_spi_alloc_master() helper.

Fixes: 9b00bc7b ("spi: spi-gpio: Rewrite to use GPIO descriptors")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: <stable@vger.kernel.org> # v4.17+: 5e844cc3: spi: Introduce device-managed SPI controller allocation
Cc: <stable@vger.kernel.org> # v5.1-: 8b797490: spi: gpio: Make sure spi_master_put() is called in every error path
Cc: <stable@vger.kernel.org> # v5.1-: 45beec35: spi: bitbang: Introduce spi_bitbang_init()
Cc: <stable@vger.kernel.org> # v5.1-: 79567c1a: spi: gpio: Use devm_spi_register_master()
Cc: <stable@vger.kernel.org> # v5.4-: d3b0ffa1: spi: gpio: prevent memory leak in spi_gpio_probe
Cc: <stable@vger.kernel.org> # v4.17+
Cc: Navid Emamdoost <navid.emamdoost@gmail.com>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Link: https://lore.kernel.org/r/86eaed27431c3d709e3748eb76ceecbfc790dd37.1607286887.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>