Re: [PATCH for-5.10] spi: gpio: Don't leak SPI master in probe error path

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Nov 16, 2020 at 9:44 AM Lukas Wunner <lukas@xxxxxxxxx> wrote:

> 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 8b797490b4db ("spi: gpio: Make sure
> spi_master_put() is called in every error path") and 79567c1a321e ("spi:
> gpio: Use devm_spi_register_master()"), which sought to plug leaks
> introduced by 9b00bc7b901f ("spi: spi-gpio: Rewrite to use GPIO
> descriptors") but missed this remaining leak.
>
> The situation was later aggravated by commit d3b0ffa1d75d ("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: 9b00bc7b901f ("spi: spi-gpio: Rewrite to use GPIO descriptors")
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.17+: 5e844cc37a5c: spi: Introduce device-managed SPI controller allocation
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.1-: 8b797490b4db: spi: gpio: Make sure spi_master_put() is called in every error path
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.1-: 45beec351998: spi: bitbang: Introduce spi_bitbang_init()
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.1-: 79567c1a321e: spi: gpio: Use devm_spi_register_master()
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.4-: d3b0ffa1d75d: spi: gpio: prevent memory leak in spi_gpio_probe
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.17+
> Cc: Navid Emamdoost <navid.emamdoost@xxxxxxxxx>
> Cc: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>

That's a really good fix. Thanks to looking into this!
Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

Yours,
Linus Walleij