net, neigh: Reject creating NUD_PERMANENT with NTF_MANAGED entries

The combination of NUD_PERMANENT + NTF_MANAGED is not supported and does
not make sense either given the former indicates a static/fixed neighbor
entry whereas the latter a dynamically resolved one. While it is possible
to transition from one over to the other, we should however reject such
creation attempts.

Fixes: 7482e3841d52 ("net, neigh: Add NTF_MANAGED flag for managed neighbor entries")
Suggested-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 922b9ed..47931c8 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1999,15 +1999,20 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 
        neigh = neigh_lookup(tbl, dst, dev);
        if (neigh == NULL) {
-               bool exempt_from_gc;
+               bool ndm_permanent  = ndm->ndm_state & NUD_PERMANENT;
+               bool exempt_from_gc = ndm_permanent ||
+                                     ndm_flags & NTF_EXT_LEARNED;
 
                if (!(nlh->nlmsg_flags & NLM_F_CREATE)) {
                        err = -ENOENT;
                        goto out;
                }
+               if (ndm_permanent && (ndm_flags & NTF_MANAGED)) {
+                       NL_SET_ERR_MSG(extack, "Invalid NTF_* flag for permanent entry");
+                       err = -EINVAL;
+                       goto out;
+               }
 
-               exempt_from_gc = ndm->ndm_state & NUD_PERMANENT ||
-                                ndm_flags & NTF_EXT_LEARNED;
                neigh = ___neigh_create(tbl, dst, dev,
                                        ndm_flags &
                                        (NTF_EXT_LEARNED | NTF_MANAGED),