netfilter: nf_tables: don't use position attribute on rule replacement

Its possible to set both HANDLE and POSITION when replacing a rule.
In this case, the rule at POSITION gets replaced using the
userspace-provided handle.  Rule handles are supposed to be generated
by the kernel only.

Duplicate handles should be harmless, however better disable this "feature"
by only checking for the POSITION attribute on insert operations.

Fixes: 5e94846686d0 ("netfilter: nf_tables: add insert operation")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index dd577e7d100cb7a53bfea5ade954c8a5d6138ac6..e496030fdc3b84fa68c0377b67e04fbace19f32e 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -2589,17 +2589,14 @@ static int nf_tables_newrule(struct net *net, struct sock *nlsk,
 
                if (chain->use == UINT_MAX)
                        return -EOVERFLOW;
-       }
-
-       if (nla[NFTA_RULE_POSITION]) {
-               if (!(nlh->nlmsg_flags & NLM_F_CREATE))
-                       return -EOPNOTSUPP;
 
-               pos_handle = be64_to_cpu(nla_get_be64(nla[NFTA_RULE_POSITION]));
-               old_rule = __nft_rule_lookup(chain, pos_handle);
-               if (IS_ERR(old_rule)) {
-                       NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_POSITION]);
-                       return PTR_ERR(old_rule);
+               if (nla[NFTA_RULE_POSITION]) {
+                       pos_handle = be64_to_cpu(nla_get_be64(nla[NFTA_RULE_POSITION]));
+                       old_rule = __nft_rule_lookup(chain, pos_handle);
+                       if (IS_ERR(old_rule)) {
+                               NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_POSITION]);
+                               return PTR_ERR(old_rule);
+                       }
                }
        }