CVE-2025-39941

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

zram: fix slot write race condition

Parallel concurrent writes to the same zram index result in leaked

zsmalloc handles. Schematically we can have something like this:

CPU0 CPU1

zram_slot_lock()

zs_free(handle)

zram_slot_lock()

zram_slot_lock()

zs_free(handle)

zram_slot_lock()

compress compress

handle = zs_malloc() handle = zs_malloc()

zram_slot_lock

zram_set_handle(handle)

zram_slot_lock

zram_slot_lock

zram_set_handle(handle)

zram_slot_lock

Either CPU0 or CPU1 zsmalloc handle will leak because zs_free() is done

too early. In fact, we need to reset zram entry right before we set its

new handle, all under the same slot lock scope.