2024-01-10 09:58:53

by Udipto Goswami

Subject: [PATCH v5] usb: core: Prevent null pointer dereference in update_port_device_state

Currently, the function update_port_device_state gets the usb_hub from
udev->parent by calling usb_hub_to_struct_hub.
However, in case the actconfig or the maxchild is 0, the usb_hub would
be NULL and upon further accessing to get port_dev would result in null
pointer dereference.

Fix this by introducing an if check after the usb_hub is populated.

Fixes: 83cb2604f641 ("usb: core: add sysfs entry for usb device state")
Cc: [email protected]
Signed-off-by: Udipto Goswami <[email protected]>
---
v5: Addressed nit picks in commit and the comment.
v4: Fixed minor mistakes in the comment.
v3: Re-wrote the comment for better context.
v2: Introduced comment for the if check & CC'ed stable.

drivers/usb/core/hub.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index ffd7c99e24a3..48409d51ea43 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2053,9 +2053,19 @@ static void update_port_device_state(struct usb_device *udev)

if (udev->parent) {
hub = usb_hub_to_struct_hub(udev->parent);
- port_dev = hub->ports[udev->portnum - 1];
- WRITE_ONCE(port_dev->state, udev->state);
- sysfs_notify_dirent(port_dev->state_kn);
+
+ /*
+ * The Link Layer Validation System Driver (lvstest)
+ * has a test step to unbind the hub before running the
+ * rest of the procedure. This triggers hub_disconnect
+ * which will set the hub's maxchild to 0, further
+ * resulting in usb_hub_to_struct_hub returning NULL.
+ */
+ if (hub) {
+ port_dev = hub->ports[udev->portnum - 1];
+ WRITE_ONCE(port_dev->state, udev->state);
+ sysfs_notify_dirent(port_dev->state_kn);
+ }
}
}

--
2.17.1

2024-01-10 15:40:25

by Alan Stern

Subject: Re: [PATCH v5] usb: core: Prevent null pointer dereference in update_port_device_state

On Wed, Jan 10, 2024 at 03:28:14PM +0530, Udipto Goswami wrote:
> Currently, the function update_port_device_state gets the usb_hub from
> udev->parent by calling usb_hub_to_struct_hub.
> However, in case the actconfig or the maxchild is 0, the usb_hub would
> be NULL and upon further accessing to get port_dev would result in null
> pointer dereference.
>
> Fix this by introducing an if check after the usb_hub is populated.
>
> Fixes: 83cb2604f641 ("usb: core: add sysfs entry for usb device state")
> Cc: [email protected]
> Signed-off-by: Udipto Goswami <[email protected]>
> ---
> v5: Addressed nit picks in commit and the comment.
> v4: Fixed minor mistakes in the comment.
> v3: Re-wrote the comment for better context.
> v2: Introduced comment for the if check & CC'ed stable.

Reviewed-by: Alan Stern <[email protected]>

> drivers/usb/core/hub.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index ffd7c99e24a3..48409d51ea43 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2053,9 +2053,19 @@ static void update_port_device_state(struct usb_device *udev)
>
> if (udev->parent) {
> hub = usb_hub_to_struct_hub(udev->parent);
> - port_dev = hub->ports[udev->portnum - 1];
> - WRITE_ONCE(port_dev->state, udev->state);
> - sysfs_notify_dirent(port_dev->state_kn);
> +
> + /*
> + * The Link Layer Validation System Driver (lvstest)
> + * has a test step to unbind the hub before running the
> + * rest of the procedure. This triggers hub_disconnect
> + * which will set the hub's maxchild to 0, further
> + * resulting in usb_hub_to_struct_hub returning NULL.
> + */
> + if (hub) {
> + port_dev = hub->ports[udev->portnum - 1];
> + WRITE_ONCE(port_dev->state, udev->state);
> + sysfs_notify_dirent(port_dev->state_kn);
> + }
> }
> }
>
> --
> 2.17.1
>