CVE-2026-72446: ALSA: usb-audio: qcom: reject stream disable with no active interface

In the Linux kernel, the following vulnerability has been resolved:

ALSA: usb-audio: qcom: reject stream disable with no active interface

handleuaudiostreamreq() resolves an interface index with infoidxfromifnum(), which returns -EINVAL when no interface matches. The enable branch and the response: cleanup label both guard against a negative index, but the disable branch does not: it forms info = &uadev[pcmcardnum].info[infoidx] and dereferences it.

uadev[].info is a pointer allocated only when a stream is first enabled, so a negative infoidx on the disable path is unsafe in two ways:

- If the card was never enabled, .info is NULL and &info[-EINVAL] is a wild pointer; reading info->dataeppipe faults (kernel oops).

- If the card was enabled at least once (.info allocated) and the disable names an interface that does not match, &info[-EINVAL] points before the allocation; info->dataeppipe / info->synceppipe are an out-of-bounds slab read and, when non-zero, an out-of-bounds 4-byte write (both pipe fields are cleared to 0). That is memory corruption, not just a NULL dereference.

The request is reachable from unprivileged local userspace over AFQIPCRTR. Reject a disable request with no resolved interface, matching the guard the enable path already has.