linux-kernel - [PATCH 6.12.y 6.6.y 6.1.y 5.15.y 5.10.y 5.4.y] ALSA: usb-audio: fix race condition to UAF in snd_usbmidi

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Message-Id: <20251007173134.440372-1-aha310510@gmail.com>
Date: Wed,  8 Oct 2025 02:31:34 +0900
From: Jeongjun Park <aha310510@...il.com>
To: stable@...r.kernel.org
Cc: Takashi Iwai <tiwai@...e.de>,
	syzbot+f02665daa2abeef4a947@...kaller.appspotmail.com,
	Clemens Ladisch <clemens@...isch.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jeongjun Park <aha310510@...il.com>
Subject: [PATCH 6.12.y 6.6.y 6.1.y 5.15.y 5.10.y 5.4.y] ALSA: usb-audio: fix race condition to UAF in snd_usbmidi_free

From: Jeongjun Park <aha310510@...il.com>

[ Upstream commit 9f2c0ac1423d5f267e7f1d1940780fc764b0fee3 ]

The previous commit 0718a78f6a9f ("ALSA: usb-audio: Kill timer properly at
removal") patched a UAF issue caused by the error timer.

However, because the error timer kill added in this patch occurs after the
endpoint delete, a race condition to UAF still occurs, albeit rarely.

Additionally, since kill-cleanup for urb is also missing, freed memory can
be accessed in interrupt context related to urb, which can cause UAF.

Therefore, to prevent this, error timer and urb must be killed before
freeing the heap memory.

Cc: <stable@...r.kernel.org>
Reported-by: syzbot+f02665daa2abeef4a947@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947
Fixes: 0718a78f6a9f ("ALSA: usb-audio: Kill timer properly at removal")
Signed-off-by: Jeongjun Park <aha310510@...il.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
---
 sound/usb/midi.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index c3de2b137435..461e183680da 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1522,15 +1522,14 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
 {
 	int i;
 
+	if (!umidi->disconnected)
+		snd_usbmidi_disconnect(&umidi->list);
+
 	for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
 		struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];
-		if (ep->out)
-			snd_usbmidi_out_endpoint_delete(ep->out);
-		if (ep->in)
-			snd_usbmidi_in_endpoint_delete(ep->in);
+		kfree(ep->out);
 	}
 	mutex_destroy(&umidi->mutex);
-	timer_shutdown_sync(&umidi->error_timer);
 	kfree(umidi);
 }
 
--