ALSA: FCP: Use a private URB for the notification endpoint

Overview

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.

Affected

• Linux >= 46757a3e7d50dac923888e7fbe68377736f13c70 < 65aceb45ca91ddb7f7ed178821f481b34da35543
• Linux >= 46757a3e7d50dac923888e7fbe68377736f13c70 < 5da21a434171e8ecf1d992c6f1d84c0c706fd395
• Linux >= 46757a3e7d50dac923888e7fbe68377736f13c70 < 6db3c1d7e2872c9904e05ca8e0515920776a3c9c
• Linux >= 46757a3e7d50dac923888e7fbe68377736f13c70 < 918b8d231c571c50a00efe92ffc8404a537a0490
• Linux 6.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.