queue-5.10/alsa-seq-clear-variable-event-pointer-on-read.patch

From 705dd6dcbc0ea87351c660c1a6443f85f1001c76 Mon Sep 17 00:00:00 2001
From: Kyle Zeng <kylebot@openai.com>
Date: Sat, 6 Jun 2026 17:41:29 -0700
Subject: ALSA: seq: Clear variable event pointer on read

From: Kyle Zeng <kylebot@openai.com>

commit 705dd6dcbc0ea87351c660c1a6443f85f1001c76 upstream.

snd_seq_read() copies a queued variable-length event header to userspace
before expanding the payload. Queued variable-length events use
SNDRV_SEQ_EXT_CHAINED internally, and data.ext.ptr points at the first
extension cell.

The read side strips SNDRV_SEQ_EXT_* bits from data.ext.len before the
copy, but it leaves data.ext.ptr untouched. A userspace sequencer client
can therefore write a direct variable event to itself and read back the
extension-cell kernel address from the returned header.

Clear the temporary header pointer before copy_to_user(). The original
queued event remains unchanged and is still passed to
snd_seq_expand_var_event(), so payload expansion keeps using the
internal chain.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Link: https://patch.msgid.link/20260607004129.61345-1-kylebot@openai.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Roman Demidov <roman.demidov.nn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/core/seq/seq_clientmgr.c |    1 +
 1 file changed, 1 insertion(+)

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -441,6 +441,7 @@ static ssize_t snd_seq_read(struct file
 			struct snd_seq_event tmpev;
 			tmpev = cell->event;
 			tmpev.data.ext.len &= ~SNDRV_SEQ_EXT_MASK;
+			tmpev.data.ext.ptr = NULL;
 			if (copy_to_user(buf, &tmpev, sizeof(struct snd_seq_event))) {
 				err = -EFAULT;
 				break;