CVE-2026-64479

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

ALSA: seq: Fix uninitialised heap leak in snd_seq_event_dup()

snd_seq_event_dup() copies an incoming event into a pool cell and, in

the UMP-enabled build, clears the trailing cell->ump.raw.extra word that

the memcpy() did not cover. The guard deciding whether to clear it

compares the copied size against sizeof(cell->event):

memcpy(&cell->ump, event, size);

if (size < sizeof(cell->event))

cell->ump.raw.extra = 0;

For a legacy (non-UMP) event, size == sizeof(struct snd_seq_event) ==

sizeof(cell->event), so the condition is false and the extra word keeps

stale data. The cell pool is allocated with kvmalloc() (not zeroed) and

cells are reused via a free list, so that word holds uninitialised heap

or leftover event data.

When such a cell is delivered to a UMP client (client->midi_version > 0)

that set SNDRV_SEQ_FILTER_NO_CONVERT -- so the legacy event reaches it

unconverted -- snd_seq_read() reads it out as the larger struct

snd_seq_ump_event and copies the stale word to user space, a 4-byte

kernel heap infoleak to an unprivileged /dev/snd/seq client.

Compare against sizeof(cell->ump) instead, so the trailing word is zeroed

for every event shorter than the UMP cell.