CVE-2026-98912: ALSA: seq: oss: Reject reads that cannot fit the next event

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

ALSA: seq: oss: Reject reads that cannot fit the next event

sndseqossread() checks whether the next queued OSS sequencer event fits in the remaining userspace buffer before removing it from the read queue.

The check is inverted. It currently stops when the event is smaller than the remaining buffer, so a normal 4-byte event is not copied for an 8-byte read buffer. Conversely, an 8-byte event can be copied for a smaller read count.

Break only when the remaining userspace buffer is smaller than the next event, and report -EINVAL if no complete event has been copied. This prevents an undersized read from looking like end-of-file while leaving the event queued for a later read with a large enough buffer.