* Elena Reshetova <elena.reshet...@intel.com> [2019-01-16 13:20:27]: > 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 uprobe.ref is used as pure reference counter. > Convert it to refcount_t and fix up the operations. > > **Important note for maintainers: > > Some functions from refcount_t API defined in lib/refcount.c > have different memory ordering guarantees than their atomic > counterparts. > The full comparison can be seen in > https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon > in state to be merged to the documentation tree. > Normally the differences should not matter since refcount_t provides > enough guarantees to satisfy the refcounting use cases, but in > some rare cases it might matter. > Please double check that you don't have some undocumented > memory guarantees for this variable usage. > > For the uprobe.ref it might make a difference > in following places: > - put_uprobe(): decrement in refcount_dec_and_test() only > provides RELEASE ordering and control dependency on success > vs. fully ordered atomic counterpart > > Suggested-by: Kees Cook <keesc...@chromium.org> > Reviewed-by: David Windsor <dwind...@gmail.com> > Reviewed-by: Hans Liljestrand <ishkam...@gmail.com> > Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> > --- > kernel/events/uprobes.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) >
Looks good to me. Reviewed-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com> -- Thanks and Regards Srikar Dronamraju
