CVE-2022-50307

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/0e501fd0f38e42304bfa0d46a812d93f80294a87
• https://git.kernel.org/stable/c/106ab66cf5467726ca5ead51623043d37c06820a
• https://git.kernel.org/stable/c/1b6074112742f65ece71b0f299ca5a6a887d2db6

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