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SubjectRe: [PATCH 1/4] bcache: convert cached_dev.count from atomic_t to refcount_t
On 10/20/2017 12:37 AM, Elena Reshetova wrote:
> atomic_t variables are currently used to implement reference
> counters with the following properties:
> - counter is initialized to 1 using atomic_set()
> - a resource is freed upon counter reaching zero
> - once counter reaches zero, its further
> increments aren't allowed
> - counter schema uses basic atomic operations
> (set, inc, inc_not_zero, dec_and_test, etc.)
> Such atomic variables should be converted to a newly provided
> refcount_t type and API that prevents accidental counter overflows
> and underflows. This is important since overflows and underflows
> can lead to use-after-free situation and be exploitable.
> The variable cached_dev.count is used as pure reference counter.
> Convert it to refcount_t and fix up the operations.
> Suggested-by: Kees Cook <>
> Reviewed-by: David Windsor <>
> Reviewed-by: Hans Liljestrand <>
> Signed-off-by: Elena Reshetova <>

Reviewed-by: Michael Lyle <>

Thanks for this-- I'm including it in my tree for possible inclusion in
4.15 (I've already sent my main chunk of changes upwards).


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