netfilter: ebtables: don't attempt to allocate 0-sized compat array

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>

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 032e0fe459408a734f8d10b326bf41f59e9f9606..28a4c3490359ccb5cc8a27e684dcfe56a13e5c40 100644 (file)
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1825,13 +1825,14 @@ static int compat_table_info(const struct ebt_table_info *info,
 {
        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);