From 11ff7288beb2b7da889a014aff0a7b80bf8efcf3 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Wed, 6 Jun 2018 12:14:56 +0200 Subject: [PATCH] netfilter: ebtables: reject non-bridge targets the ebtables evaluation loop expects targets to return positive values (jumps), or negative values (absolute verdicts). This is completely different from what xtables does. In xtables, targets are expected to return the standard netfilter verdicts, i.e. NF_DROP, NF_ACCEPT, etc. ebtables will consider these as jumps. Therefore reject any target found due to unspec fallback. v2: also reject watchers. ebtables ignores their return value, so a target that assumes skb ownership (and returns NF_STOLEN) causes use-after-free. The only watchers in the 'ebtables' front-end are log and nflog; both have AF_BRIDGE specific wrappers on kernel side. Reported-by: syzbot+2b43f681169a2a0d306a@syzkaller.appspotmail.com Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/bridge/netfilter/ebtables.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c index 5f459c8b7937..08a65e4a77d0 100644 --- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -396,6 +396,12 @@ ebt_check_watcher(struct ebt_entry_watcher *w, struct xt_tgchk_param *par, watcher = xt_request_find_target(NFPROTO_BRIDGE, w->u.name, 0); if (IS_ERR(watcher)) return PTR_ERR(watcher); + + if (watcher->family != NFPROTO_BRIDGE) { + module_put(watcher->me); + return -ENOENT; + } + w->u.watcher = watcher; par->target = watcher; @@ -715,6 +721,13 @@ ebt_check_entry(struct ebt_entry *e, struct net *net, goto cleanup_watchers; } + /* Reject UNSPEC, xtables verdicts/return values are incompatible */ + if (target->family != NFPROTO_BRIDGE) { + module_put(target->me); + ret = -ENOENT; + goto cleanup_watchers; + } + t->u.target = target; if (t->u.target == &ebt_standard_target) { if (gap < sizeof(struct ebt_standard_target)) { -- 2.30.2