From e58a171d35e32e6e8c37cfe0e8a94406732a331f Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Fri, 17 Feb 2023 23:20:06 +0100 Subject: 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: c58dd2dd443c ("netfilter: Can't fail and free after table replacement") Reported-by: syzbot+f61594de72d6705aea03@syzkaller.appspotmail.com Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/bridge/netfilter/ebtables.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/bridge') diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c index ce5dfa3babd2..757ec46fc45a 100644 --- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -1090,7 +1090,7 @@ 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); -- cgit