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Change History

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.

https://git.kernel.org/stable/c/ce4be9e4307c5a60701ff6e0cafa74caffdc54ce

https://git.kernel.org/stable/c/ff750e9f2c4d63854c33967d1646b5e89a9a19a2