netfilter: nf_tables: report EEXIST on overlaps

Replace EBUSY by EEXIST in the following cases:

- If the user adds a chain with a different configuration such as different
  type, hook and priority.

- If the user adds a non-base chain that clashes with an existing basechain.

- If the user adds a { key : value } mapping element and the key exists
  but the value differs.

- If the device already belongs to an existing flowtable.

User describe that this error reporting is confusing:

- https://bugzilla.netfilter.org/show_bug.cgi?id=1176
- https://bugzilla.netfilter.org/show_bug.cgi?id=1413Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -2097,7 +2097,7 @@ static int nf_tables_updchain(struct nft_ctx *ctx, u8 genmask, u8 policy,
 
 	if (nla[NFTA_CHAIN_HOOK]) {
 		if (!nft_is_base_chain(chain))
-			return -EBUSY;
+			return -EEXIST;
 
 		err = nft_chain_parse_hook(ctx->net, nla, &hook, ctx->family,
 					   false);
@@ -2107,21 +2107,21 @@ static int nf_tables_updchain(struct nft_ctx *ctx, u8 genmask, u8 policy,
 		basechain = nft_base_chain(chain);
 		if (basechain->type != hook.type) {
 			nft_chain_release_hook(&hook);
-			return -EBUSY;
+			return -EEXIST;
 		}
 
 		if (ctx->family == NFPROTO_NETDEV) {
 			if (!nft_hook_list_equal(&basechain->hook_list,
 						 &hook.list)) {
 				nft_chain_release_hook(&hook);
-				return -EBUSY;
+				return -EEXIST;
 			}
 		} else {
 			ops = &basechain->ops;
 			if (ops->hooknum != hook.num ||
 			    ops->priority != hook.priority) {
 				nft_chain_release_hook(&hook);
-				return -EBUSY;
+				return -EEXIST;
 			}
 		}
 		nft_chain_release_hook(&hook);
@@ -5262,10 +5262,8 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			if (nft_set_ext_exists(ext, NFT_SET_EXT_DATA) ^
 			    nft_set_ext_exists(ext2, NFT_SET_EXT_DATA) ||
 			    nft_set_ext_exists(ext, NFT_SET_EXT_OBJREF) ^
-			    nft_set_ext_exists(ext2, NFT_SET_EXT_OBJREF)) {
-				err = -EBUSY;
+			    nft_set_ext_exists(ext2, NFT_SET_EXT_OBJREF))
 				goto err_element_clash;
-			}
 			if ((nft_set_ext_exists(ext, NFT_SET_EXT_DATA) &&
 			     nft_set_ext_exists(ext2, NFT_SET_EXT_DATA) &&
 			     memcmp(nft_set_ext_data(ext),
@@ -5273,7 +5271,7 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			    (nft_set_ext_exists(ext, NFT_SET_EXT_OBJREF) &&
 			     nft_set_ext_exists(ext2, NFT_SET_EXT_OBJREF) &&
 			     *nft_set_ext_obj(ext) != *nft_set_ext_obj(ext2)))
-				err = -EBUSY;
+				goto err_element_clash;
 			else if (!(nlmsg_flags & NLM_F_EXCL))
 				err = 0;
 		} else if (err == -ENOTEMPTY) {
@@ -6423,7 +6421,7 @@ static int nft_register_flowtable_net_hooks(struct net *net,
 			list_for_each_entry(hook2, &ft->hook_list, list) {
 				if (hook->ops.dev == hook2->ops.dev &&
 				    hook->ops.pf == hook2->ops.pf) {
-					err = -EBUSY;
+					err = -EEXIST;
 					goto err_unregister_net_hooks;
 				}
 			}