| From 3ef6970d22f10f4c0e5f2961563c01284e641be1 Mon Sep 17 00:00:00 2001 |
| From: Florian Westphal <fw@strlen.de> |
| Date: Tue, 2 Jul 2019 21:41:40 +0200 |
| Subject: netfilter: nfnetlink: avoid deadlock due to synchronous |
| request_module |
| |
| [ 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 733d3e4a30d85..2cee032af46d2 100644 |
| --- a/net/netfilter/nfnetlink.c |
| +++ b/net/netfilter/nfnetlink.c |
| @@ -530,7 +530,7 @@ 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 |
| |
