[PATCH 4.16 02/72] netfilter: ebtables: dont attempt to allocate 0-sized compat array

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.16-stable review patch.  If anyone has any objections, please let me know.

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

From: Florian Westphal <fw@strlen.de>

commit 3f1e53abff84cf40b1adb3455d480dd295bf42e8 upstream.

Dmitry reports 32bit ebtables on 64bit kernel got broken by
a recent change that returns -EINVAL when ruleset has no entries.

ebtables however only counts user-defined chains, so for the
initial table nentries will be 0.

Don't try to allocate the compat array in this case, as no user
defined rules exist no rule will need 64bit translation.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: 7d7d7e02111e9 ("netfilter: compat: reject huge allocation requests")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/bridge/netfilter/ebtables.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1821,13 +1821,14 @@ static int compat_table_info(const struc
 {
 	unsigned int size = info->entries_size;
 	const void *entries = info->entries;
-	int ret;
 
 	newinfo->entries_size = size;
-
-	ret = xt_compat_init_offsets(NFPROTO_BRIDGE, info->nentries);
-	if (ret)
-		return ret;
+	if (info->nentries) {
+		int ret = xt_compat_init_offsets(NFPROTO_BRIDGE,
+						 info->nentries);
+		if (ret)
+			return ret;
+	}
 
 	return EBT_ENTRY_ITERATE(entries, size, compat_calc_entry, info,
 							entries, newinfo);