Re: [PATCH v3] ssb: Fix potential NULL pointer dereference in ssb_device_uevent

[Jonas Gorski]

Hi

On Wed, 6 Mar 2024 at 13:32, Rand Deeb <rand.sec96@xxxxxxxxx> wrote:
>
> The ssb_device_uevent function first attempts to convert the 'dev' pointer
> to 'struct ssb_device *'. However, it mistakenly dereferences 'dev' before
> performing the NULL check, potentially leading to a NULL pointer
> dereference if 'dev' is NULL.
>
> To fix this issue, this patch moves the NULL check before dereferencing the
> 'dev' pointer, ensuring that the pointer is valid before attempting to use
> it.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Signed-off-by: Rand Deeb <rand.sec96@xxxxxxxxx>
> ---
>  drivers/ssb/main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/ssb/main.c b/drivers/ssb/main.c
> index b9934b9c2d70..070a99a4180c 100644
> --- a/drivers/ssb/main.c
> +++ b/drivers/ssb/main.c
> @@ -341,11 +341,13 @@ static int ssb_bus_match(struct device *dev, struct device_driver *drv)
>
>  static int ssb_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
>  {
> -       const struct ssb_device *ssb_dev = dev_to_ssb_dev(dev);
> +       const struct ssb_device *ssb_dev;
>
>         if (!dev)
>                 return -ENODEV;
>
> +       ssb_dev = dev_to_ssb_dev(dev);
> +

The NULL check is what needs to be fixed/removed, not the code
surrounding it. This function will be called from dev_uevent() [1]
where dev cannot be NULL. So a NULL dereference cannot happen.

Most other implementors of bus_type::uevent have no NULL check. To be
precise, there is only one other implementor with a NULL check,
rio_uevent(), and none of the other ones have one. See e.g.
bcma_device_uevent(), memstick_uevent(), mips_cdmm_uevent(), or
fsl_mc_bus_uevent().

[1] https://elixir.bootlin.com/linux/v6.7.8/source/drivers/base/core.c#L2590

Best Regards,
Jonas