CVE-2023-54324

In the Linux kernel, the following vulnerability has been resolved:

dm: fix a race condition in retrieve_deps

There's a race condition in the multipath target when retrievedeps races with multipathmessage calling dmgetdevice and dmputdevice. retrieve_deps walks the list of open devices without holding any lock but multipath may add or remove devices to the list while it is running. The end result may be memory corruption or use-after-free memory access.

See this description of a UAF with multipath_message(): https://listman.redhat.com/archives/dm-devel/2022-October/052373.html

Fix this bug by introducing a new rw semaphore "deviceslock". We grab deviceslock for read in retrievedeps and we grab it for write in dmgetdevice and dmput_device.