Bug 2401425 (CVE-2025-39941)

Summary: CVE-2025-39941 kernel: zram: fix slot write race condition
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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Description OSIDB Bzimport 2025-10-04 08:02:38 UTC 
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.
Comment 1 Jon Moroney 2025-10-06 15:49:27 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025100418-CVE-2025-39941-f256@gregkh/T