s390/dcssblk: fix kernel crash with list_add corruption

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: s390/dcssblk: fix kernel crash with list_add corruption Commit fb08a1908cb1 ("dax: simplify the dax_device <-> gendisk association") introduced new logic for gendisk association, requiring drivers to explicitly call dax_add_host() and dax_remove_host(). For dcssblk driver, some dax_remove_host() calls were missing, e.g. in device remove path. The commit also broke error handling for out_dax case in device add path, resulting in an extra put_device() w/o the previous get_device() in that case. This lead to stale xarray entries after device add / remove cycles. In the case when a previously used struct gendisk pointer (xarray index) would be used again, because blk_alloc_disk() happened to return such a pointer, the xa_insert() in dax_add_host() would fail and go to out_dax, doing the extra put_device() in the error path. In combination with an already flawed error handling in dcssblk (device_register() cleanup), which needs to be addressed in a separate patch, this resulted in a missing device_del() / klist_del(), and eventually in the kernel crash with list_add corruption on a subsequent device_add() / klist_add(). Fix this by adding the missing dax_remove_host() calls, and also move the put_device() in the error path to restore the previous logic.

References

• https://git.kernel.org/stable/c/6489ec0107860345bc57dcde39e63dfb05ac5c11
• https://git.kernel.org/stable/c/b7ad75c77349beb4983b9f27108d9b3f33ae1413
• https://git.kernel.org/stable/c/b5c531a9a7d8e047c90c909f09cef06a9f8e62f4
• https://git.kernel.org/stable/c/c8f40a0bccefd613748d080147469a4652d6e74c