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.

This vulnerability does not impact Red Hat Enterprise Linux or other supported products because the underlying flaw was introduced in newer upstream kernel revisions not included in Red Hat kernel releases. The issue arises from synchronization gaps during concurrent write operations to compressed in-memory block devices, which could allow a local user to cause memory exhaustion over time. Because supported Red Hat platforms do not incorporate the affected changes in the zram subsystem, systems remain unaffected.