* [PATCH AUTOSEL 4.9 01/22] netfilter: nfnetlink: avoid deadlock due to synchronous request_module
@ 2019-08-02 13:25 Sasha Levin
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From: Sasha Levin @ 2019-08-02 13:25 UTC (permalink / raw)
To: linux-kernel, stable
Cc: Florian Westphal, Thomas Jarosch, Juliana Rodrigueiro,
Pablo Neira Ayuso, Sasha Levin, netfilter-devel, coreteam,
netdev
From: Florian Westphal <fw@strlen.de>
[ Upstream commit 1b0890cd60829bd51455dc5ad689ed58c4408227 ]
Thomas and Juliana report a deadlock when running:
(rmmod nf_conntrack_netlink/xfrm_user)
conntrack -e NEW -E &
modprobe -v xfrm_user
They provided following analysis:
conntrack -e NEW -E
netlink_bind()
netlink_lock_table() -> increases "nl_table_users"
nfnetlink_bind()
# does not unlock the table as it's locked by netlink_bind()
__request_module()
call_usermodehelper_exec()
This triggers "modprobe nf_conntrack_netlink" from kernel, netlink_bind()
won't return until modprobe process is done.
"modprobe xfrm_user":
xfrm_user_init()
register_pernet_subsys()
-> grab pernet_ops_rwsem
..
netlink_table_grab()
calls schedule() as "nl_table_users" is non-zero
so modprobe is blocked because netlink_bind() increased
nl_table_users while also holding pernet_ops_rwsem.
"modprobe nf_conntrack_netlink" runs and inits nf_conntrack_netlink:
ctnetlink_init()
register_pernet_subsys()
-> blocks on "pernet_ops_rwsem" thanks to xfrm_user module
both modprobe processes wait on one another -- neither can make
progress.
Switch netlink_bind() to "nowait" modprobe -- this releases the netlink
table lock, which then allows both modprobe instances to complete.
Reported-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Reported-by: Juliana Rodrigueiro <juliana.rodrigueiro@intra2net.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nfnetlink.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 2278d9ab723bf..9837a61cb3e3b 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -490,7 +490,7 @@ static int nfnetlink_bind(struct net *net, int group)
ss = nfnetlink_get_subsys(type << 8);
rcu_read_unlock();
if (!ss)
- request_module("nfnetlink-subsys-%d", type);
+ request_module_nowait("nfnetlink-subsys-%d", type);
return 0;
}
#endif
--
2.20.1
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