Messages in this thread | | | Date | Tue, 15 Jan 2008 15:11:30 -0800 | From | Stephen Hemminger <> | Subject | Re: [PATCH] net_device refcnt bug when NFQUEUEing bridged packets |
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On Wed, 16 Jan 2008 00:05:44 +0100 Jan Christoph Nordholz <hesso@pool.math.tu-berlin.de> wrote:
> Hi, > > I came across the following bug a few weeks ago (which still applies to > 2.6.24-rc7): > > Packets that are to be sent out over a bridge device are skb_clone()d in > br_loop() before traversing the appropriate (FORWARD/OUTPUT) NF chain. > The copies made by skb_clone() share their nf_bridge metadata with the > original, which is no problem usually. > If however one or more packets of a br_loop() run end up in a NFQUEUE, > their shared nf_bridge metadata causes trouble when they are about to be > reinjected: nf_reinject() decrements the net_device refcounts that were > previously upped when queueing the packet in __nf_queue(), but as > skb->nf_bridge->physoutdev points to the same device for all these > packets, most (if not all) of them will affect the wrong refcnt. > > (I originally encountered the bug on a Xen host because the hypervisor > refused to shutdown a virtual device with non-zero refcount... but it is > perfectly reproducible with a standard kernel, too, although it was a > bit more tedious to create a test scenario, involving a couple of UMLs.) > > I'd suggest to make a real copy of the nf_bridge member in br_loop() if > CONFIG_BRIDGE_NETFILTER is defined - I've attached a patch that illus- > trates how to fix the bug (and the machine I've found the bug on is > running a kernel with this patch since weeks and has not had any > refcount anomalies since), but I admit it is ugly, returning the reference > acquired by __nf_copy() and then copying manually... > > Please tell me where that logic should really go (skbuff.h? br_netfilter.c?) > so I can wrap up a final and CodingStyle-conformant version, or feel free > to simply apply a modified version. > > > Regards, > > Jan > >
Please submit a bug to kernel bugzilla. Not sure that the patch is the proper way to fix this.
-- Stephen Hemminger <stephen.hemminger@vyatta.com>
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