Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
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.
Details
- Affected product:
- AlmaLinux 9.2 ESU , TuxCare 9.6 ESU
- Affected packages:
- kernel @ 5.14.0 (+1 more)
In the Linux kernel, the following vulnerability has been resolved:
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.