On Sun, Feb 3, 2019 at 10:51 PM Reshetova, Elena <elena.reshet...@intel.com> wrote: > > > > * 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> > > Thank you very much Srikar! > Would you be able to take this patch to integration?
Steve can you pick this up with Srikar's Reviewed-by? -- Kees Cook
