PROBLEM with summary: Re: [PATCH] netfilter: per netns nf_conntrack_cachep

Jon Masters
2010-02-02T16:58:23Z

On Tue, 2010-02-02 at 11:46 -0500, Jon Masters wrote:
> On Tue, 2010-02-02 at 06:35 -0500, Jon Masters wrote:
>
> > I think there's something more fundamental going on here.
>
> What happens is the conntrack code attempts to free
> nf_conntrack_untracked back into the SL[U]B cache from which it
> allocates other ct's. There's just one problem...that's a static struct
> not from the cache. So, this is why we end up with the SLAB being
> corrupted and the address immediately following the
> nf_conntrack_untracked being corrupted.
>
> I shoved some debug comments into the destroy code to see if we were
> trying to free nf_conntrack_untracked, and bingo. I have shoved a panic
> in there now, will send you a backtrace.

So we attach after starting a VM due to icmpv6_error setting the ct in
some incoming skb to the "untracked" catchall one. Then we panic when I
force a panic if attempting to free the nf_conntrack_untracked static
struct with this backtrace:

#5 0xffffffff81455884 in panic (
fmt=0xffffffff81ec51e0 "JCM: nf_conntrack_destroy: trying to destroy
nf_conntrack_untracked!\n")
at kernel/panic.c:73
#6 0xffffffff813d266c in nf_conntrack_destroy (nfct=<value optimized
out>) at net/netfilter/core.c:244
#7 0xffffffff813abd97 in nf_conntrack_put (skb=0xffff880223b8b700) at
include/linux/skbuff.h:1924
#8 skb_release_head_state (skb=0xffff880223b8b700) at
net/core/skbuff.c:402
#9 0xffffffff813abaf9 in skb_release_all (skb=0xffff880223b8b700) at
net/core/skbuff.c:420
#10 __kfree_skb (skb=0xffff880223b8b700) at net/core/skbuff.c:435
#11 0xffffffff813abbfe in kfree_skb (skb=0xffff880223b8b700) at
net/core/skbuff.c:456

Could you please add (or recommend for me to test) some logic to catch
attempts to free the nf_conntrack_untracked and prevent it? Also, maybe
in the init_net code you could remove the re-initialization of the
untracked conntrack each time a namespace is created?

Thanks!

Jon.