⚠️ ALSA: usb-audio: qcom: reject stream disable with no active interface (Linux Linux)

Description

In the Linux kernel, the following vulnerability has been resolved: ALSA: usb-audio: qcom: reject stream disable with no active interface handle_uaudio_stream_req() resolves an interface index with info_idx_from_ifnum(), 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[pcm_card_num].info[info_idx] and dereferences it. uadev[].info is a pointer allocated only when a stream is first enabled, so a negative info_idx 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->data_ep_pipe 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->data_ep_pipe / info->sync_ep_pipe 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 AF_QIPCRTR. Reject a disable request with no resolved interface, matching the guard the enable path already has.