On 16-11-23 05:58 PM, Cong Wang wrote: > Roi reported we could have a race condition where in ->classify() path > we dereference tp->root and meanwhile a parallel ->destroy() makes it > a NULL. > > This is possible because ->destroy() could be called when deleting > a filter to check if we are the last one in tp, this tp is still > linked and visible at that time. > > The root cause of this problem is the semantic of ->destroy(), it > does two things (for non-force case): > > 1) check if tp is empty > 2) if tp is empty we could really destroy it > > and its caller, if cares, needs to check its return value to see if > it is really destroyed. Therefore we can't unlink tp unless we know > it is empty. > > As suggested by Daniel, we could actually move the test logic to ->delete() > so that we can safely unlink tp after ->delete() tells us the last one is > just deleted and before ->destroy(). > > What's more, even we unlink it before ->destroy(), it could still have > readers since we don't wait for a grace period here, we should not modify > tp->root in ->destroy() either. > > Fixes: 1e052be69d04 ("net_sched: destroy proto tp when all filters are gone") > Reported-by: Roi Dayan <r...@mellanox.com> > Cc: Daniel Borkmann <dan...@iogearbox.net> > Cc: John Fastabend <john.fastab...@gmail.com> > Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com> > ---
Hi Cong, Thanks a lot for doing this. Can you rebase it on top of Daniel's patch though, [PATCH net] net, sched: respect rcu grace period on cls destruction And then push the NULL pointer work for the cls_fw and cls_route classifiers into another patch. Then I believe the last thing to make this correct is to convert the call_rcu() paths to call_rcu_bh(). .John