CVE-2026-93084firmware: arm_scmi: Drop handle on protocol bind failures

Official description

In the Linux kernel, the following vulnerability has been resolved: firmware: arm_scmi: Drop handle on protocol bind failures The SCMI bus notifier acquires an SCMI handle when the driver core emits BUS_NOTIFY_BIND_DRIVER, before invoking the protocol driver probe callback. The protocol probe path only checks whether sdev->handle is set. If device_link_add() fails after the handle has been acquired, the protocol device can still bind with a valid handle but without the dependency link to the SCMI parent. A concurrent parent unbind can then miss the child and tear down the SCMI instance while the child still holds a handle into it. If the protocol driver probe later fails, for example with -EPROBE_DEFER, the driver core emits BUS_NOTIFY_DRIVER_NOT_BOUND rather than BUS_NOTIFY_UNBOUND_DRIVER. The SCMI notifier only released the handle on BUS_NOTIFY_UNBOUND_DRIVER, so each failed protocol-device bind leaked the SCMI instance users refcount and left sdev->handle set after the failed probe. Make the link helper report failure and drop the acquired handle if the link cannot be created. Also handle BUS_NOTIFY_DRIVER_NOT_BOUND in the same cleanup path used for unbind so failed probes balance the earlier BUS_NOTIFY_BIND_DRIVER acquisition.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/b5377e690cd4fe87ee52fcf067c9929414ea8f4e
• https://git.kernel.org/stable/c/0f860db24ee95e5da4866303a35e55098b9641b3
• https://git.kernel.org/stable/c/df273eced7cec550465fd1bb82a5d2c3c7d3c437
• https://git.kernel.org/stable/c/a54dc23e8bd2246c28eafffa60b4634f0d1a11cc
• https://git.kernel.org/stable/c/77d2985d1e80e67f32026fc03e975c4c83cc543d
• https://git.kernel.org/stable/c/e3a5c30d233ca5d3e799a80da806554c703bda13