Patch "s390/cio: fix out-of-bounds access on cio_ignore free" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    s390/cio: fix out-of-bounds access on cio_ignore free

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     s390-cio-fix-out-of-bounds-access-on-cio_ignore-free.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit bfbf966318d4d292b6d891f5fdec10e4648a54d8
Author: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
Date:   Fri Oct 14 12:24:58 2022 +0200

    s390/cio: fix out-of-bounds access on cio_ignore free
    
    [ Upstream commit 1b6074112742f65ece71b0f299ca5a6a887d2db6 ]
    
    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.
    
    Fixes: 172da89ed0ea ("s390/cio: avoid excessive path-verification requests")
    Fixes: 0c3812c347bf ("s390/cio: derive cdev information only for IO-subchannels")
    Cc: <stable@xxxxxxxxxxxxxxx> # v5.15
    Reported-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx>
    Reviewed-by: Vineeth Vijayan <vneethv@xxxxxxxxxxxxx>
    Signed-off-by: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
    Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index ce9e7517430f..2ba9e0135565 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -792,13 +792,9 @@ 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;
 }