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 zramslotlock() zsfree(handle) zramslotlock() zramslotlock() zsfree(handle) zramslotlock()

compress compress handle = zsmalloc() handle = zsmalloc() zramslotlock zramsethandle(handle) zramslotlock zramslotlock zramsethandle(handle) zramslotlock

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.