Commit 16bfc60e authored Jun 06, 2018 by Florian Westphal Committed by Greg Kroah-Hartman Jul 22, 2018

netfilter: ebtables: reject non-bridge targets



commit 11ff7288beb2b7da889a014aff0a7b80bf8efcf3 upstream.

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 <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 776bfa10

net/bridge/netfilter/ebtables.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -402,6 +402,12 @@ 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;
		@@ -722,6 +728,13 @@ 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)) {