Re: net: GPF in netlink_getsockbyportid

Daniel Borkmann [off-list ref] wrote:

On 01/23/2016 08:25 PM, Florian Westphal wrote:

quoted

Dmitry Vyukov [off-list ref] wrote:

[ CC nf-devel, not sure if its nfnetlink fault or NETLINK_MMAP ]

quoted

The following program causes GPF in netlink_getsockbyportid:

[..]

quoted

CONFIG_NETLINK_MMAP and nfnetlink batching strike in unison :-/

root cause is in nfnetlink_rcv_batch():

296 replay:
297         status = 0;
298
299         skb = netlink_skb_clone(oskb, GFP_KERNEL);

The clone op doesn't copy oskb->sk, so we oops in
__netlink_alloc_skb -> netlink_getsockbyportid() when nfnetlink_rcv_batch
tries to send netlink ack.

If indeed oskb is the mmap'ed netlink skb, then it's not even allowed
to call into skb_clone()

Right, but in this case there is no mmap'd netlink sk involved -- we
crash when we try to look up dst netlink socket to see if there is an
mmap'd ring attached.

[ and that code isn't there with CONFIG_NETLINK_MMAP=n ].