On Fri, Feb 5, 2021 at 6:14 AM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
>
> commit 3d1cf435e201d1fd63e4346b141881aed086effd upstream
>
> If the device passed as the target (second argument) to
> device_is_dependent() is not completely registered (that is, it has
> been initialized, but not added yet), but the parent pointer of it
> is set, it may be missing from the list of the parent's children
> and device_for_each_child() called by device_is_dependent() cannot
> be relied on to catch that dependency.
>
> For this reason, modify device_is_dependent() to check the ancestors
> of the target device by following its parent pointer in addition to
> the device_for_each_child() walk.
>
> Fixes: 9ed9895370ae ("driver core: Functional dependencies tracking support")
> Reported-by: Stephan Gerhold <stephan@xxxxxxxxxxx>
> Tested-by: Stephan Gerhold <stephan@xxxxxxxxxxx>
> Reviewed-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Link: https://lore.kernel.org/r/17705994.d592GUb2YH@kreacher
> Cc: stable <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> drivers/base/core.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -96,6 +96,16 @@ void device_links_read_unlock(int not_us
> }
> #endif /* !CONFIG_SRCU */
>
> +static bool device_is_ancestor(struct device *dev, struct device *target)
> +{
> + while (target->parent) {
> + target = target->parent;
> + if (dev == target)
> + return true;
> + }
> + return false;
> +}
> +
> /**
> * device_is_dependent - Check if one device depends on another one
> * @dev: Device to check dependencies for.
> @@ -109,7 +119,12 @@ static int device_is_dependent(struct de
> struct device_link *link;
> int ret;
>
> - if (dev == target)
> + /*
> + * The "ancestors" check is needed to catch the case when the target
> + * device has not been completely initialized yet and it is still
> + * missing from the list of children of its parent device.
> + */
> + if (dev == target || device_is_ancestor(dev, target))
> return 1;
>
> ret = device_for_each_child(dev, target, device_is_dependent);
>
>
I think 4.14 device links API is so busted it's not worth patching
this. It's not a memory leak or any kind of security issue.
Stephan, are you seeing this issue in 4.14 or even care about it?
-Saravana
