[PATCH ebtables-nft] ebtables: fix over-eager -o checks on custom chains

[Florian Westphal <fw@strlen.de>]

Arturo reports ebtables-nft reports an error when -o is
used in custom chains:

-A MYCHAIN -o someif
makes ebtables-nft exit with an error:
"Use -o only in OUTPUT, FORWARD and POSTROUTING chains."

Problem is that all the "-o" checks expect <= NF_BR_POST_ROUTING
to mean "builtin", so -1 mistakenly leads to the checks being active.

Reported-by: Arturo Borrero Gonzalez <arturo@netfilter.org>
Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1347
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 iptables/xtables-eb.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/iptables/xtables-eb.c b/iptables/xtables-eb.c
index 121ecbecd0b6..3b03daef28eb 100644
--- a/iptables/xtables-eb.c
+++ b/iptables/xtables-eb.c
@@ -197,7 +197,8 @@ int ebt_get_current_chain(const char *chain)
 	else if (strcmp(chain, "POSTROUTING") == 0)
 		return NF_BR_POST_ROUTING;
 
-	return -1;
+	/* placeholder for user defined chain */
+	return NF_BR_NUMHOOKS;
 }
 
 /*
@@ -1223,7 +1224,7 @@ print_zero:
 	cs.eb.ethproto = htons(cs.eb.ethproto);
 
 	if (command == 'P') {
-		if (selected_chain < 0) {
+		if (selected_chain >= NF_BR_NUMHOOKS) {
 			ret = ebt_set_user_chain_policy(h, *table, chain, policy);
 		} else {
 			if (strcmp(policy, "RETURN") == 0) {
-- 
2.21.0