[PATCH 5.15 874/917] net, neigh: Enable state migration between NUD_PERMANENT and NTF_USE

From: Greg Kroah-Hartman
Date: Mon Nov 15 2021 - 19:38:07 EST

From: Daniel Borkmann <daniel@xxxxxxxxxxxxx>

[ Upstream commit 3dc20f4762c62d3b3f0940644881ed818aa7b2f5 ]

Currently, it is not possible to migrate a neighbor entry between NUD_PERMANENT
state and NTF_USE flag with a dynamic NUD state from a user space control plane.
Similarly, it is not possible to add/remove NTF_EXT_LEARNED flag from an existing
neighbor entry in combination with NTF_USE flag.

This is due to the latter directly calling into neigh_event_send() without any
meta data updates as happening in __neigh_update(). Thus, to enable this use
case, extend the latter with a NEIGH_UPDATE_F_USE flag where we break the
NUD_PERMANENT state in particular so that a latter neigh_event_send() is able
to re-resolve a neighbor entry.

Before fix, NUD_PERMANENT -> NUD_* & NTF_USE:

# ./ip/ip n replace 192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a PERMANENT
[...]
# ./ip/ip n replace 192.168.178.30 dev enp5s0 use extern_learn
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a PERMANENT
[...]

As can be seen, despite the admin-triggered replace, the entry remains in the
NUD_PERMANENT state.

After fix, NUD_PERMANENT -> NUD_* & NTF_USE:

# ./ip/ip n replace 192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a PERMANENT
[...]
# ./ip/ip n replace 192.168.178.30 dev enp5s0 use extern_learn
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a extern_learn REACHABLE
[...]
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a extern_learn STALE
[...]
# ./ip/ip n replace 192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a PERMANENT
[...]

After the fix, the admin-triggered replace switches to a dynamic state from
the NTF_USE flag which triggered a new neighbor resolution. Likewise, we can
transition back from there, if needed, into NUD_PERMANENT.

Similar before/after behavior can be observed for below transitions:

Before fix, NTF_USE -> NTF_USE | NTF_EXT_LEARNED -> NTF_USE:

# ./ip/ip n replace 192.168.178.30 dev enp5s0 use
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a REACHABLE
[...]
# ./ip/ip n replace 192.168.178.30 dev enp5s0 use extern_learn
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a REACHABLE
[...]

After fix, NTF_USE -> NTF_USE | NTF_EXT_LEARNED -> NTF_USE:

# ./ip/ip n replace 192.168.178.30 dev enp5s0 use
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a REACHABLE
[...]
# ./ip/ip n replace 192.168.178.30 dev enp5s0 use extern_learn
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a extern_learn REACHABLE
[...]
# ./ip/ip n replace 192.168.178.30 dev enp5s0 use
# ./ip/ip n
192.168.178.30 dev enp5s0 lladdr f4:8c:50:5e:71:9a REACHABLE
[..]

Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Roopa Prabhu <roopa@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/net/neighbour.h | 1 +
net/core/neighbour.c | 22 +++++++++++++---------
2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 990f9b1d17092..d5767e25509cc 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -253,6 +253,7 @@ static inline void *neighbour_priv(const struct neighbour *n)
#define NEIGH_UPDATE_F_OVERRIDE 0x00000001
#define NEIGH_UPDATE_F_WEAK_OVERRIDE 0x00000002
#define NEIGH_UPDATE_F_OVERRIDE_ISROUTER 0x00000004
+#define NEIGH_UPDATE_F_USE 0x10000000
#define NEIGH_UPDATE_F_EXT_LEARNED 0x20000000
#define NEIGH_UPDATE_F_ISROUTER 0x40000000
#define NEIGH_UPDATE_F_ADMIN 0x80000000
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 8457d5f97022b..3e58037a8ae6f 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1217,7 +1217,7 @@ static void neigh_update_hhs(struct neighbour *neigh)
lladdr instead of overriding it
if it is different.
NEIGH_UPDATE_F_ADMIN means that the change is administrative.
-
+ NEIGH_UPDATE_F_USE means that the entry is user triggered.
NEIGH_UPDATE_F_OVERRIDE_ISROUTER allows to override existing
NTF_ROUTER flag.
NEIGH_UPDATE_F_ISROUTER indicates if the neighbour is known as
@@ -1255,6 +1255,12 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
goto out;

ext_learn_change = neigh_update_ext_learned(neigh, flags, &notify);
+ if (flags & NEIGH_UPDATE_F_USE) {
+ new = old & ~NUD_PERMANENT;
+ neigh->nud_state = new;
+ err = 0;
+ goto out;
+ }

if (!(new & NUD_VALID)) {
neigh_del_timer(neigh);
@@ -1963,22 +1969,20 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,

if (protocol)
neigh->protocol = protocol;
-
if (ndm->ndm_flags & NTF_EXT_LEARNED)
flags |= NEIGH_UPDATE_F_EXT_LEARNED;
-
if (ndm->ndm_flags & NTF_ROUTER)
flags |= NEIGH_UPDATE_F_ISROUTER;
+ if (ndm->ndm_flags & NTF_USE)
+ flags |= NEIGH_UPDATE_F_USE;

- if (ndm->ndm_flags & NTF_USE) {
+ err = __neigh_update(neigh, lladdr, ndm->ndm_state, flags,
+ NETLINK_CB(skb).portid, extack);
+ if (!err && ndm->ndm_flags & NTF_USE) {
neigh_event_send(neigh, NULL);
err = 0;
- } else
- err = __neigh_update(neigh, lladdr, ndm->ndm_state, flags,
- NETLINK_CB(skb).portid, extack);
-
+ }
neigh_release(neigh);
-
out:
return err;
}
--
2.33.0