In the Linux kernel, the following vulnerability has been resolved: scsi: ch: Do not keep references to data transfer element devices ch_r

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

scsi: ch: Do not keep references to data transfer element devices

ch_readconfig() looks up the scsi_device of every data transfer element
whose SCSI id the changer reports in READ ELEMENT STATUS, and stores it in
ch->dt[]. scsi_device_lookup() takes a reference, and nothing ever drops
it: ch_destroy() frees the array with kfree(). ch->dt[] is read nowhere
else - it only supplies the vendor, model and revision printed in the same
loop.

Once such a drive is removed, its scsi_device can never be released. It
stays on the host's device list at its address, so a new device there is
refused by anything that walks the list - target_core_pscsi reports
"scsi_device_get() failed for H:C:T:L" - and the low-level driver's module
can no longer be unloaded. Only a reboot recovers.

It shows with any changer that reports its drives' ids; with the mhvtl
virtual library (IBM 3573-TL personality), each create and remove of a
library with four drives leaves four references behind, counted by the
module's use count in lsmod. With ch not bound the count is unchanged, and
with this patch applied it is unchanged too.

Drop the reference as soon as the name has been printed, and remove the now
unused dt[] array. That also removes the array leaked when ch_probe() fails
after ch_readconfig().

The same leak was reported with an RFC patch in 2022, which was not merged.