From: HyeongJun An Date: Tue, 23 Jun 2026 23:38:40 +0000 (+0900) Subject: ALSA: seq: Fix uninitialised heap leak in snd_seq_event_dup() X-Git-Tag: v7.2-rc1~5^2~8 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=435990e25bf1f4af3e6df12a6fbfd1f7ba4a97d4;p=thirdparty%2Fkernel%2Flinux.git 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. Fixes: 46397622a3fa ("ALSA: seq: Add UMP support") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: HyeongJun An Link: https://patch.msgid.link/20260623233841.853326-1-sammiee5311@gmail.com Signed-off-by: Takashi Iwai --- diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c index ca9f6db0022c8..209b08c2a9408 100644 --- a/sound/core/seq/seq_memory.c +++ b/sound/core/seq/seq_memory.c @@ -364,7 +364,7 @@ int snd_seq_event_dup(struct snd_seq_pool *pool, struct snd_seq_event *event, size = snd_seq_event_packet_size(event); memcpy(&cell->ump, event, size); #if IS_ENABLED(CONFIG_SND_SEQ_UMP) - if (size < sizeof(cell->event)) + if (size < sizeof(cell->ump)) cell->ump.raw.extra = 0; #endif