CVE-2026-80816 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: FCP: Use a private URB for the notification endpoint
fcp_init_notify() used mixer->urb, which snd_usb_mixer_status_create() allocates for the optional UAC2 status interrupt endpoint and mixer.c kills, resubmits and frees. On a device with that endpoint, fcp_init_notify()'s "already set up" early return fires on the status URB and returns success without doing anything. No FCP notification URB is submitted, and cmd_done is left zeroed because it is initialised past that early return and nowhere else. fcp_init() then issues init1_opcode and wait_for_completion_timeout() would crash adding to the zeroed wait.head. fcp_cleanup_urb() would also kill and free mixer.c's status URB.
Use a separate URB in fcp_data, and initialise cmd_done in fcp_init_private() where fcp_data is allocated. fcp_init_notify() is reached again after suspend via fcp_reinit(), and the URB kill path in fcp_notify() completes cmd_done, leaving a stale count that would satisfy the next command's wait before the device ACKs. Use reinit_completion() to clear it.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel audio subsystem contains a critical concurrency and initialization flaw within the ALSA FCP driver implementation involving improper resource management of USB Request Blocks, or URBs. The vulnerability stems from fcp_init_notify incorrectly sharing a mixer status URB allocated for optional Universal Audio Class 2 status interrupt endpoints with its own notification endpoint requirements. This architectural oversight leads to premature termination and incorrect state handling during device initialization and subsequent power transitions such as suspend and resume cycles.
When the system encounters a USB audio device equipped with an optional UAC2 status interrupt endpoint, fcp_init_notify detects that the shared mixer->urb is already configured by snd_usb_mixer_status_create. Consequently, it triggers an early return indicating success without establishing any FCP notification URBs. This results in cmd_done remaining zeroed because its initialization occurs after this premature exit point and never executes elsewhere within the function scope. The absence of a properly initialized completion structure creates a dangerous state where subsequent operations proceed with invalid synchronization primitives.
The operational impact manifests when fcp_init subsequently issues an init1_opcode command, triggering wait_for_completion_timeout to monitor for device acknowledgment. Because cmd_done was left zeroed and never properly linked to the URB's completion handler, the kernel attempts to add a non-existent or malformed entry to the wait queue head structure. This action precipitates a kernel panic due to memory corruption within the wait list data structures. Furthermore, fcp_cleanup_urb erroneously kills and frees the mixer.c status URB intended for general audio mixing purposes rather than FCP-specific notifications, potentially disrupting other subsystem components relying on that endpoint for real-time status updates.
The vulnerability extends beyond initial boot sequences into runtime power management scenarios involving suspend and resume operations. Upon resuming from a suspended state via fcp_reinit(), the driver re-enters fcp_init_notify which again encounters the pre-existing mixer URB configuration. The existing kill path in fcp_notify completes cmd_done prematurely, leaving it with a stale count value that falsely satisfies subsequent command waits before the device actually acknowledges them. This race condition allows commands to proceed without proper hardware synchronization, leading to undefined behavior and potential system instability during active usage after power state transitions.
To resolve these issues, the fix mandates allocating a dedicated private URB within fcp_data specifically for FCP notification endpoints rather than sharing resources with general mixer status operations. Initialization of cmd_done must occur in fcp_init_private where fcp_data is allocated ensuring proper lifecycle management aligned with the new resource allocation strategy. Additionally reinit_completion calls are introduced to explicitly clear stale completion counts before issuing new commands after resume events preventing false positives in synchronization primitives and restoring correct ordering between driver actions and device acknowledgments.
This vulnerability aligns with CWE-362 Concurrent Execution using Shared Resource without Synchronization as it involves improper handling of shared kernel structures during concurrent initialization paths. It also relates to CWE-457 Use of Uninitialized Variable since cmd_done remains zeroed due to early returns bypassing its setup logic. From an ATT&CK perspective this represents a Local Privilege Escalation vector through Denial of Service via Kernel Panic allowing attackers with local access to crash the system or potentially exploit memory corruption states for further exploitation if adjacent vulnerabilities exist in the wait queue implementation details.
Mitigation strategies require applying vendor-provided kernel patches that implement isolated URB allocation per functional endpoint and enforce strict initialization ordering within driver probe routines. System administrators should ensure timely updates of ALSA components and monitor logs for USB enumeration failures or audio subsystem crashes following suspend-resume cycles. Developers reviewing similar drivers must audit all shared resource allocations ensuring no single URB serves multiple distinct functional purposes with differing lifecycle requirements to prevent state corruption during concurrent access patterns typical in high-frequency interrupt-driven hardware interactions.