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Message-Id: <20191227181435.7644-3-sashal@kernel.org> Date: Fri, 27 Dec 2019 13:14:00 -0500 From: Sasha Levin <sashal@...nel.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Florian Westphal <fw@...len.de>, Pablo Neira Ayuso <pablo@...filter.org>, Sasha Levin <sashal@...nel.org>, netfilter-devel@...r.kernel.org, coreteam@...filter.org, netdev@...r.kernel.org Subject: [PATCH AUTOSEL 4.9 03/38] netfilter: ctnetlink: netns exit must wait for callbacks From: Florian Westphal <fw@...len.de> [ Upstream commit 18a110b022a5c02e7dc9f6109d0bd93e58ac6ebb ] Curtis Taylor and Jon Maxwell reported and debugged a crash on 3.10 based kernel. Crash occurs in ctnetlink_conntrack_events because net->nfnl socket is NULL. The nfnl socket was set to NULL by netns destruction running on another cpu. The exiting network namespace calls the relevant destructors in the following order: 1. ctnetlink_net_exit_batch This nulls out the event callback pointer in struct netns. 2. nfnetlink_net_exit_batch This nulls net->nfnl socket and frees it. 3. nf_conntrack_cleanup_net_list This removes all remaining conntrack entries. This is order is correct. The only explanation for the crash so ar is: cpu1: conntrack is dying, eviction occurs: -> nf_ct_delete() -> nf_conntrack_event_report \ -> nf_conntrack_eventmask_report -> notify->fcn() (== ctnetlink_conntrack_events). cpu1: a. fetches rcu protected pointer to obtain ctnetlink event callback. b. gets interrupted. cpu2: runs netns exit handlers: a runs ctnetlink destructor, event cb pointer set to NULL. b runs nfnetlink destructor, nfnl socket is closed and set to NULL. cpu1: c. resumes and trips over NULL net->nfnl. Problem appears to be that ctnetlink_net_exit_batch only prevents future callers of nf_conntrack_eventmask_report() from obtaining the callback. It doesn't wait of other cpus that might have already obtained the callbacks address. I don't see anything in upstream kernels that would prevent similar crash: We need to wait for all cpus to have exited the event callback. Fixes: 9592a5c01e79dbc59eb56fa ("netfilter: ctnetlink: netns support") Signed-off-by: Florian Westphal <fw@...len.de> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org> Signed-off-by: Sasha Levin <sashal@...nel.org> --- net/netfilter/nf_conntrack_netlink.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c index deea281ab169..5e28702c801f 100644 --- a/net/netfilter/nf_conntrack_netlink.c +++ b/net/netfilter/nf_conntrack_netlink.c @@ -3388,6 +3388,9 @@ static void __net_exit ctnetlink_net_exit_batch(struct list_head *net_exit_list) list_for_each_entry(net, net_exit_list, exit_list) ctnetlink_net_exit(net); + + /* wait for other cpus until they are done with ctnl_notifiers */ + synchronize_rcu(); } static struct pernet_operations ctnetlink_net_ops = { -- 2.20.1
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