CVE-2026-74278

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

ALSA: seq: Fix kernel heap address leak in bounce_error_event()

The comment above bounce_error_event() documents that user clients

should receive SNDRV_SEQ_EVENT_BOUNCE with the original event embedded

as variable-length data, while kernel clients should receive

SNDRV_SEQ_EVENT_KERNEL_ERROR with a quoted kernel pointer.

However, the implementation unconditionally uses

SNDRV_SEQ_EVENT_KERNEL_ERROR with data.quote.event set to the raw

struct snd_seq_event pointer for all clients. When a bounce error

event is delivered to a USER_CLIENT via snd_seq_read(), the kernel

heap address in data.quote.event is exposed to userspace through

copy_to_user() in the fixed-length branch.

This is a distinct leak path from the one addressed by commit

705dd6dcbc0e ("ALSA: seq: Clear variable event pointer on read"),

which sanitizes data.ext.ptr in the variable-length branch of

snd_seq_read(). The bounce_error_event() leak uses fixed-length

events that take the else branch where no sanitization occurs.

Differentiate the bounce event by client type. For USER_CLIENT,

send SNDRV_SEQ_EVENT_BOUNCE with SNDRV_SEQ_EVENT_LENGTH_VARIABLE

and data.ext pointing to the original event. The variable-length

path in snd_seq_event_dup() copies the event data into chained

cells, and snd_seq_expand_var_event() copies only the content --

never the pointer -- to userspace. For KERNEL_CLIENT, keep the

existing SNDRV_SEQ_EVENT_KERNEL_ERROR behavior with the quoted

pointer.