FAILED: patch "[PATCH] s390/cio: fix out-of-bounds access on cio_ignore free" 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]>.

Possible dependencies:

1b6074112742 ("s390/cio: fix out-of-bounds access on cio_ignore free") 0c3812c347bf ("s390/cio: derive cdev information only for IO-subchannels")

thanks,

greg k-h

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

From 1b6074112742f65ece71b0f299ca5a6a887d2db6 Mon Sep 17 00:00:00 2001
From: Peter Oberparleiter <[email protected]>
Date: Fri, 14 Oct 2022 12:24:58 +0200
Subject: [PATCH] s390/cio: fix out-of-bounds access on cio_ignore free

The channel-subsystem-driver scans for newly available devices whenever device-IDs are removed from the cio_ignore list using a command such as:

echo free >/proc/cio_ignore

Since an I/O device scan might interfer with running I/Os, commit 172da89ed0ea ("s390/cio: avoid excessive path-verification requests") introduced an optimization to exclude online devices from the scan.

The newly added check for online devices incorrectly assumes that an I/O-subchannel's drvdata points to a struct io_subchannel_private. For devices that are bound to a non-default I/O subchannel driver, such as the vfio_ccw driver, this results in an out-of-bounds read access during each scan.

Fix this by changing the scan logic to rely on a driver-independent online indication. For this we can use struct subchannel->config.ena, which is the driver's requested subchannel-enabled state. Since I/Os can only be started on enabled subchannels, this matches the intent of the original optimization of not scanning devices where I/O might be running.

index 913b6ddd040b..c7db95398500 100644
@@ -753,13 +753,9 @@ static int __unset_online(struct device *dev, void *data)
 {
 	struct idset *set = data;
 	struct subchannel *sch = to_subchannel(dev);
-	struct ccw_device *cdev;
 
-	if (sch->st == SUBCHANNEL_TYPE_IO) {
-		cdev = sch_get_cdev(sch);
-		if (cdev && cdev->online)
-			idset_sch_del(set, sch->schid);
-	}
+	if (sch->st == SUBCHANNEL_TYPE_IO && sch->config.ena)
+		idset_sch_del(set, sch->schid);
 
 	return 0;
 }