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From: Pablo Neira Ayuso <pablo@netfilter.org>
To: netfilter-devel@vger.kernel.org
Cc: davem@davemloft.net, netdev@vger.kernel.org
Subject: [PATCH 4/9] netfilter: ctnetlink: make it safer when checking the ct helper name
Date: Fri, 14 Apr 2017 02:26:46 +0200
Message-ID: <1492129611-29336-5-git-send-email-pablo@netfilter.org> (raw)
In-Reply-To: <1492129611-29336-1-git-send-email-pablo@netfilter.org>

From: Liping Zhang <zlpnobody@gmail.com>

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: f95d7a46bc57 ("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>
---
 net/netfilter/nf_conntrack_netlink.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 06d28ac663df..f9c643bc1a8e 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -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, "")) {
-- 
2.1.4

  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-14  0:26 [PATCH 0/9] Netfilter fixes for net Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 1/9] netfilter: xt_TCPMSS: add more sanity tests on tcph->doff Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 2/9] netfilter: ctnetlink: using bit to represent the ct event Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 3/9] netfilter: helper: Add the rcu lock when call __nf_conntrack_helper_find Pablo Neira Ayuso
2017-04-14  0:26 ` Pablo Neira Ayuso [this message]
2017-04-14  0:26 ` [PATCH 5/9] netfilter: make it safer during the inet6_dev->addr_list traversal Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 6/9] netfilter: ctnetlink: skip dumping expect when nfct_help(ct) is NULL Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 7/9] netfilter: nf_ct_expect: use proper RCU list traversal/update APIs Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 8/9] netfilter: nft_hash: do not dump the auto generated seed Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 9/9] netfilter: ipt_CLUSTERIP: Fix wrong conntrack netns refcnt usage Pablo Neira Ayuso
2017-04-14 14:59 ` [PATCH 0/9] Netfilter fixes for net David Miller

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