hello Cong, thanks for looking at this!
On Mon, 2021-04-19 at 11:46 -0700, Cong Wang wrote:
> On Mon, Apr 19, 2021 at 8:24 AM Davide Caratti <dcara...@redhat.com> wrote:
> > diff --git a/net/sched/sch_frag.c b/net/sched/sch_frag.c
> > index e1e77d3fb6c0..8c06381391d6 100644
> > --- a/net/sched/sch_frag.c
> > +++ b/net/sched/sch_frag.c
> > @@ -90,16 +90,16 @@ static int sch_fragment(struct net *net, struct sk_buff
> > *skb,
> > }
> >
> > if (skb_protocol(skb, true) == htons(ETH_P_IP)) {
> > - struct dst_entry sch_frag_dst;
> > + struct rtable sch_frag_rt = { 0 };
>
> Is setting these fields 0 sufficient here? Because normally a struct table
> is initialized by rt_dst_alloc() which sets several of them to non-zero,
> notably, rt->rt_type and rt->rt_uncached.
>
> Similar for the IPv6 part, which is initialized by rt6_info_init().
for what we do now in openvswitch and sch_frag, that should be
sufficient: a similar thing is done by br_netfilter [1], apparently for
the same "refragmentation" purposes. On a fedora host (running 5.10, but
it shouldn't be much different than current Linux), I just dumped
'fake_rtable' from a bridge device:
# ip link add name test-br0 type bridge
# ip link set dev test-br0 up
# ip link add name test-port0 type dummy
# ip link set dev test-port0 master test-br0 up
# crash
[...]
crash> net
NET_DEVICE NAME IP ADDRESS(ES)
[...]
ffff89fb44ed8000 test-br0
ffff89fbfc45c000 test-port0
crash> p sizeof(struct net_device)
$12 = 3200
crash> p ((struct net_bridge*)(0xffff89fb44ed8000 + 3200))->fake_rtable
$13 = {
dst = {
dev = 0xffff89fb44ed8000,
ops = 0xffffffffc0afef40,
_metrics = 18446744072647256257,
expires = 0,
xfrm = 0x0,
input = 0x0,
output = 0x0,
flags = 18, <-- that should be DST_NOXFRM | DST_FAKE_RTABLE
obsolete = 0,
header_len = 0,
trailer_len = 0,
__refcnt = {
counter = 1
},
__use = 0,
lastuse = 0,
lwtstate = 0x0,
callback_head = {
next = 0x0,
func = 0x0
},
error = 0,
__pad = 0,
tclassid = 0
},
rt_genid = 0,
rt_flags = 0,
rt_type = 0,
rt_is_input = 0 '\000',
rt_uses_gateway = 0 '\000',
rt_iif = 0,
rt_gw_family = 0 '\000',
{
rt_gw4 = 0,
rt_gw6 = {
in6_u = {
u6_addr8 =
"\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
u6_addr16 = {0, 0, 0, 0, 0, 0, 0, 0},
u6_addr32 = {0, 0, 0, 0}
}
}
},
rt_mtu_locked = 0,
rt_pmtu = 0,
rt_uncached = {
next = 0x0,
prev = 0x0
},
rt_uncached_list = 0x0
}
only fake_rtable.dst members are set to something, the remaining are all
zero-ed.
--
davide
[1] https://elixir.bootlin.com/linux/latest/source/net/bridge/br_nf_core.c#L62
