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authorFlorian Westphal <fw@strlen.de>2019-07-02 21:41:40 +0200
committerPablo Neira Ayuso <pablo@netfilter.org>2019-07-15 07:56:58 +0200
commit1b0890cd60829bd51455dc5ad689ed58c4408227 (patch)
tree5a4e013c6ccc36c3bdebf251ac6ea807c9d630b9 /net/netfilter
parent76104862cccaeaa84fdd23e39f2610a96296291c (diff)
netfilter: nfnetlink: avoid deadlock due to synchronous request_module
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>
Diffstat (limited to 'net/netfilter')
-rw-r--r--net/netfilter/nfnetlink.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 92077d459109..4abbb452cf6c 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -578,7 +578,7 @@ 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