netfilter: ebtables: also count base chain policies

ebtables doesn't include the base chain policies in the rule count,
so we need to add them manually when we call into the x_tables core
to allocate space for the comapt offset table.

This lead syzbot to trigger:
WARNING: CPU: 1 PID: 9012 at net/netfilter/x_tables.c:649
xt_compat_add_offset.cold+0x11/0x36 net/netfilter/x_tables.c:649

Reported-by: syzbot+276ddebab3382bbf72db@syzkaller.appspotmail.com
Fixes: 2035f3ff8eaa ("netfilter: ebtables: compat: un-break 32bit setsockopt when no rules are present")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 17 insertions, 11 deletions

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index fd84b48e48b5..c8177a89f52c 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1770,20 +1770,28 @@ static int compat_calc_entry(const struct ebt_entry *e,
         return 0;
 }
 
+static int ebt_compat_init_offsets(unsigned int number)
+{
+        if (number > INT_MAX)
+                return -EINVAL;
+
+        /* also count the base chain policies */
+        number += NF_BR_NUMHOOKS;
+
+        return xt_compat_init_offsets(NFPROTO_BRIDGE, number);
+}
 
 static int compat_table_info(const struct ebt_table_info *info,
                              struct compat_ebt_replace *newinfo)
 {
         unsigned int size = info->entries_size;
         const void *entries = info->entries;
+        int ret;
 
         newinfo->entries_size = size;
-        if (info->nentries) {
-                int ret = xt_compat_init_offsets(NFPROTO_BRIDGE,
-                                                 info->nentries);
-                if (ret)
-                        return ret;
-        }
+        ret = ebt_compat_init_offsets(info->nentries);
+        if (ret)
+                return ret;
 
         return EBT_ENTRY_ITERATE(entries, size, compat_calc_entry, info,
                                                         entries, newinfo);
@@ -2234,11 +2242,9 @@ static int compat_do_replace(struct net *net, void __user *user,
 
         xt_compat_lock(NFPROTO_BRIDGE);
 
-        if (tmp.nentries) {
-                ret = xt_compat_init_offsets(NFPROTO_BRIDGE, tmp.nentries);
-                if (ret < 0)
-                        goto out_unlock;
-        }
+        ret = ebt_compat_init_offsets(tmp.nentries);
+        if (ret < 0)
+                goto out_unlock;
 
         ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state);
         if (ret < 0)