Commit 3173d5b8 authored Apr 01, 2017 by Liping Zhang Committed by Pablo Neira Ayuso Apr 08, 2017

netfilter: ctnetlink: make it safer when checking the ct helper name



One CPU is doing ctnetlink_change_helper(), while another CPU is doing
unhelp() at the same time. So even if help->helper is not NULL at first,
the later statement strcmp(help->helper->name, ...) may still access
the NULL pointer.

So we must use rcu_read_lock and rcu_dereference to avoid such _bad_
thing happen.

Fixes: f95d7a46 ("netfilter: ctnetlink: Fix regression in CTA_HELP processing")
Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

parent 8b5995d0

net/netfilter/nf_conntrack_netlink.c

+10 −5

Original line number	Diff line number	Diff line
		@@ -1488,11 +1488,16 @@ static int ctnetlink_change_helper(struct nf_conn *ct,
		* treat the second attempt as a no-op instead of returning
		* an error.
		*/
		if (help && help->helper &&
		!strcmp(help->helper->name, helpname))
		return 0;
		else
		return -EBUSY;
		err = -EBUSY;
		if (help) {
		rcu_read_lock();
		helper = rcu_dereference(help->helper);
		if (helper && !strcmp(helper->name, helpname))
		err = 0;
		rcu_read_unlock();
		}

		return err;
		}

		if (!strcmp(helpname, "")) {