Messages in this thread | | | From | Cong Wang <> | Date | Wed, 1 May 2019 17:48:19 -0700 | Subject | Re: [PATCH net] cls_matchall: avoid panic when receiving a packet before filter set |
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On Wed, May 1, 2019 at 2:27 AM Matteo Croce <mcroce@redhat.com> wrote: > > On Tue, Apr 30, 2019 at 11:25 PM Cong Wang <xiyou.wangcong@gmail.com> wrote: > > > > On Mon, Apr 29, 2019 at 10:38 AM Matteo Croce <mcroce@redhat.com> wrote: > > > > > > When a matchall classifier is added, there is a small time interval in > > > which tp->root is NULL. If we receive a packet in this small time slice > > > a NULL pointer dereference will happen, leading to a kernel panic: > > > > Hmm, why not just check tp->root against NULL in mall_classify()? > > > > Also, which is the offending commit here? Please add a Fixes: tag. > > > > Thanks. > > Hi, > > I just want to avoid an extra check which would be made for every packet. > Probably the benefit over a check is negligible, but it's still a > per-packet thing. > If you prefer a simple check, I can make a v2 that way.
Yeah, I think that is better, you can add an unlikely() for performance concern, as NULL is a rare case.
> > For the fixes tag, I didn't put it as I'm not really sure about the > offending commit. I guess it's the following, what do you think? > > commit ed76f5edccc98fa66f2337f0b3b255d6e1a568b7 > Author: Vlad Buslov <vladbu@mellanox.com> > Date: Mon Feb 11 10:55:38 2019 +0200 > > net: sched: protect filter_chain list with filter_chain_lock mutex
I think you are right, this is the commit introduced the code that inserts the tp before fully initializing it. Please Cc Vlad for your v2, in case we blame a wrong commit here.
BTW, it looks like cls_cgroup needs a same fix. Please audit other tc filters as well.
Thanks!
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