CVE-2022-49989 xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

In the Linux kernel, the following vulnerability has been resolved: xen/privcmd: fix error exit of privcmdioctldmop The error exit of privcmdioctldmop is calling unlockpages potentially with pages being NULL, leading to a NULL dereference. Additionally lockpages doesn't check for pinuserpagesfast...