netfilter: ebtables: fix table blob use-after-free

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2189550
Upstream Status: commit e58a171

commit e58a171
Author: Florian Westphal <[email protected]>
Date:   Fri Feb 17 23:20:06 2023 +0100

    netfilter: ebtables: fix table blob use-after-free

    We are not allowed to return an error at this point.
    Looking at the code it looks like ret is always 0 at this
    point, but its not.

    t = find_table_lock(net, repl->name, &ret, &ebt_mutex);

    ... this can return a valid table, with ret != 0.

    This bug causes update of table->private with the new
    blob, but then frees the blob right away in the caller.

    Syzbot report:

    BUG: KASAN: vmalloc-out-of-bounds in __ebt_unregister_table+0xc00/0xcd0 net/bridge/netfilter/ebtables.c:1168
    Read of size 4 at addr ffffc90005425000 by task kworker/u4:4/74
    Workqueue: netns cleanup_net
    Call Trace:
     kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
     __ebt_unregister_table+0xc00/0xcd0 net/bridge/netfilter/ebtables.c:1168
     ebt_unregister_table+0x35/0x40 net/bridge/netfilter/ebtables.c:1372
     ops_exit_list+0xb0/0x170 net/core/net_namespace.c:169
     cleanup_net+0x4ee/0xb10 net/core/net_namespace.c:613
    ...

    ip(6)tables appears to be ok (ret should be 0 at this point) but make
    this more obvious.

    Fixes: c58dd2d ("netfilter: Can't fail and free after table replacement")
    Reported-by: [email protected]
    Signed-off-by: Florian Westphal <[email protected]>
    Signed-off-by: Pablo Neira Ayuso <[email protected]>

Signed-off-by: Florian Westphal <[email protected]>

Author: fw-strlen

net/bridge/netfilter/ebtables.c

@@ -1053,7 +1053,7 @@ static int do_replace_finish(struct net *net, struct ebt_replace *repl,
 
 	audit_log_nfcfg(repl->name, AF_BRIDGE, repl->nentries,
 			AUDIT_XT_OP_REPLACE, GFP_KERNEL);
-	return ret;
+	return 0;
 
 free_unlock:
 	mutex_unlock(&ebt_mutex);

net/ipv4/netfilter/ip_tables.c

@@ -1044,7 +1044,6 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
 	struct xt_counters *counters;
 	struct ipt_entry *iter;
 
-	ret = 0;
 	counters = xt_counters_alloc(num_counters);
 	if (!counters) {
 		ret = -ENOMEM;
@@ -1090,7 +1089,7 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
 		net_warn_ratelimited("iptables: counters copy to user failed while replacing table\n");
 	}
 	vfree(counters);
-	return ret;
+	return 0;
 
  put_module:
 	module_put(t->me);

net/ipv6/netfilter/ip6_tables.c

@@ -1061,7 +1061,6 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
 	struct xt_counters *counters;
 	struct ip6t_entry *iter;
 
-	ret = 0;
 	counters = xt_counters_alloc(num_counters);
 	if (!counters) {
 		ret = -ENOMEM;
@@ -1107,7 +1106,7 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
 		net_warn_ratelimited("ip6tables: counters copy to user failed while replacing table\n");
 	}
 	vfree(counters);
-	return ret;
+	return 0;
 
  put_module:
 	module_put(t->me);