CVE-2026-98809Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister

Official description

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister hci_unregister_dev() disables cmd_work and cmd_timer, then calls hci_cmd_sync_clear(), whose cancel_work_sync() waits for hci_cmd_sync_work() to return. That worker dequeues and runs every entry on cmd_sync_work_list. With cmd_work disabled nothing reaches the controller, so each queued HCI command waits the full HCI_CMD_TIMEOUT (2s). The backlog has no bound. Userspace can keep queuing MGMT commands such as MGMT_OP_GET_CLOCK_INFO against a controller that doesn't answer. Closing /dev/vhci then blocks in vhci_release() for backlog * 2s: INFO: task syz-executor:5749 blocked for more than 143 seconds. cancel_work_sync hci_cmd_sync_clear hci_unregister_dev vhci_release In a local reproduction the backlog held more than 5000 entries, which comes to hours of hang. Stop the worker from taking new entries once HCI_UNREGISTER is set, and wake any request still waiting with -ENODEV before cancelling the work. The entries left over are destroyed with -ECANCELED by the existing sweep in hci_cmd_sync_clear(). They stay on the list until the work has stopped, so hci_cmd_sync_dequeue() and friends still see them. A callback already running may still issue another command, which delays unregister by at most one timeout per remaining command, not by the whole backlog.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/b06d85b114cc5fa61809f9950bca66502e0e1173
• https://git.kernel.org/stable/c/b11acfcb5925ed27fae692b27931a1ac732677fb
• https://git.kernel.org/stable/c/143bde97c4101ae68eb656c87e620c45b07a3090
• https://git.kernel.org/stable/c/7f16443a30f4e86d84ae4faf057d333b41ddb757
• https://git.kernel.org/stable/c/e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c
• https://git.kernel.org/stable/c/b1f24c1ab52345e810c42a1a81286cb5a7c92252