[PATCH 3.16 190/305] netfilter: nf_tables: don't use position attribute on rule replacement

[Ben Hutchings]

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@xxxxxxxxx>

commit 447750f281abef547be44fdcfe3bc4447b3115a8 upstream.

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@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - Don't use extack
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1767,16 +1767,13 @@ static int nf_tables_newrule(struct sock
 
 		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 = __nf_tables_rule_lookup(chain, pos_handle);
-		if (IS_ERR(old_rule))
-			return PTR_ERR(old_rule);
+		if (nla[NFTA_RULE_POSITION]) {
+			pos_handle = be64_to_cpu(nla_get_be64(nla[NFTA_RULE_POSITION]));
+			old_rule = __nf_tables_rule_lookup(chain, pos_handle);
+			if (IS_ERR(old_rule))
+				return PTR_ERR(old_rule);
+		}
 	}
 
 	nft_ctx_init(&ctx, skb, nlh, afi, table, chain, nla);