On 2018/06/14 17:49, Jesper Dangaard Brouer wrote: > On Thu, 14 Jun 2018 11:07:42 +0900 > Toshiaki Makita <makita.toshi...@lab.ntt.co.jp> wrote: > >> Commit 67f29e07e131 ("bpf: devmap introduce dev_map_enqueue") changed >> the return value type of __devmap_lookup_elem() from struct net_device * >> to struct bpf_dtab_netdev * but forgot to modify generic XDP code >> accordingly. >> Thus generic XDP incorrectly used struct bpf_dtab_netdev where struct >> net_device is expected, then skb->dev was set to invalid value. >> >> v2: >> - Fix compiler warning without CONFIG_BPF_SYSCALL. >> >> Fixes: 67f29e07e131 ("bpf: devmap introduce dev_map_enqueue") >> Signed-off-by: Toshiaki Makita <makita.toshi...@lab.ntt.co.jp> > > Thanks for catching this! > > Acked-by: Jesper Dangaard Brouer <bro...@redhat.com> > > Notice, that the current code works (and does not crash), but it is > pure luck. Because struct bpf_dtab_netdev happen to have the > net_device as the first member. > > struct bpf_dtab_netdev { > struct net_device *dev; /* must be first member, due to tracepoint */ > struct bpf_dtab *dtab; > unsigned int bit; > struct xdp_bulk_queue __percpu *bulkq; > struct rcu_head rcu; > }; >
Actually no, the current code does not work and can crash, because we need to dereference the pointer, i.e. need fwd->dev (IOW *fwd) not fwd. -- Toshiaki Makita