On Fri, 2013-02-01 at 18:08 -0800, Steve Muckle wrote: > Recently I've struggled with crashes in the xt_qtaguid netfilter module. > This module is written by Google and used with Android. The match > function in xt_qtaguid eventually tries to access > > skb->sk->sk_socket->file > > What I find is that the sk->sk_socket pointer is sometimes 0xAAAAAAAA, > or PAGE_POISON. In fact everything after the first 16 bytes of the > struct sock sk is PAGE_POISON. I've confirmed that if I change > PAGE_POISON, the values I see in the sk structure change as well. > > I was curious how this structure was being allocated/initialized and > instrumented the sk_alloc, sk_free, and sk_clone_lock functions. When > xt_qtaguid encounters a bad struct sock, that sock does not show up as > ever having been allocated (or freed). > > The struct sock is being assigned to the skb in tcb_v4_early_demux(). I > modified that function immediately after the sk is assigned from > __inet_lookup_established() to panic if the sk has a sk_socket pointer > of PAGE_POISON. I can reproduce that condition on my target by simply > attempting to mount an NFS volume. Initiating *and* aborting wget > operations also reproduces the issue - simply initiating a bunch of > wgets is not enough to trigger it. > > I have not yet been able to reproduce the bad condition when disabling > ip_early_demux via the sysctl. Any possibility this is an actual issue > with that feature? My target is an MSM using the ks8851 ethernet module. skb->sk might be a TIMEWAIT socket. Therefore, you cant blindly use skb->sk->sk_socket -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
