FAILED: patch "[PATCH] ALSA: seq: Serialize compat port-info ioctls" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 95b2e0361c88753afa030c10698be0a1a5b67650
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026100526-essential-squishy-ce6c@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 95b2e0361c88753afa030c10698be0a1a5b67650 Mon Sep 17 00:00:00 2001
From: Kyle Zeng <[email protected]>
Date: Thu, 17 Sep 2026 12:56:43 +0200
Subject: [PATCH] ALSA: seq: Serialize compat port-info ioctls

The native sequencer ioctl path serializes handler calls with client->ioctl_mutex, but the translated port-info compat path invokes the same handlers through snd_seq_kernel_client_ctl() without taking that mutex.

This lets concurrent compat CREATE_PORT requests pass the port-count check before any request reaches the serialized insertion. The computed integer port index can then exceed the address field range and wrap to an existing index. Subsequent subscriber teardown can resolve the duplicate address to the wrong port and access a freed subscriber.

Take ioctl_mutex while dispatching converted port-info requests, matching the native ioctl path. All translated port-info commands share this helper, so their accesses to the client port state are serialized as well.

index 22679dca9aae..80110501da6f 100644
@@ -44,7 +44,9 @@ static int snd_seq_call_port_info_ioctl(struct snd_seq_client *client, unsigned
 		return -EFAULT;
 	data->kernel = NULL;
 
-	err = snd_seq_kernel_client_ctl(client->number, cmd, data);
+	scoped_guard(mutex, &client->ioctl_mutex) {
+		err = snd_seq_kernel_client_ctl(client->number, cmd, data);
+	}
 	if (err < 0)
 		return err;
 

From: Kyle Zeng <[email protected]>

[ Upstream commit 95b2e0361c88753afa030c10698be0a1a5b67650 ]

The native sequencer ioctl path serializes handler calls with client->ioctl_mutex, but the translated port-info compat path invokes the same handlers through snd_seq_kernel_client_ctl() without taking that mutex.

This lets concurrent compat CREATE_PORT requests pass the port-count check before any request reaches the serialized insertion. The computed integer port index can then exceed the address field range and wrap to an existing index. Subsequent subscriber teardown can resolve the duplicate address to the wrong port and access a freed subscriber.

Take ioctl_mutex while dispatching converted port-info requests, matching the native ioctl path. All translated port-info commands share this helper, so their accesses to the client port state are serialized as well.

---
 sound/core/seq/seq_compat.c | 2 ++
 1 file changed, 2 insertions(+)

index c0ce6236dc7f1..65c385f3ef894 100644
@@ -44,7 +44,9 @@ static int snd_seq_call_port_info_ioctl(struct snd_seq_client *client, unsigned
 		goto error;
 	data->kernel = NULL;
 
+	mutex_lock(&client->ioctl_mutex);
 	err = snd_seq_kernel_client_ctl(client->number, cmd, data);
+	mutex_unlock(&client->ioctl_mutex);
 	if (err < 0)
 		goto error;
 

2.53.0