4.17-stable review patch. If anyone has any objections, please let me know.
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From: Gao Feng gfree.wind@vip.163.com
[ Upstream commit ad9852af97587b8abe8102f9ddcb05c9769656f6 ]
The helper module would be unloaded after nf_conntrack_helper_unregister, so it may cause a possible panic caused by race.
nf_ct_iterate_destroy(unhelp, me) reset the helper of conntrack as NULL, but maybe someone has gotten the helper pointer during this period. Then it would panic, when it accesses the helper and the module was unloaded.
Take an example as following: CPU0 CPU1 ctnetlink_dump_helpinfo helper = rcu_dereference(help->helper); unhelp set helper as NULL unload helper module helper->to_nlattr(skb, ct);
As above, the cpu0 tries to access the helper and its module is unloaded, then the panic happens.
Signed-off-by: Gao Feng gfree.wind@vip.163.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/netfilter/nf_conntrack_helper.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/net/netfilter/nf_conntrack_helper.c +++ b/net/netfilter/nf_conntrack_helper.c @@ -465,6 +465,11 @@ void nf_conntrack_helper_unregister(stru
nf_ct_expect_iterate_destroy(expect_iter_me, NULL); nf_ct_iterate_destroy(unhelp, me); + + /* Maybe someone has gotten the helper already when unhelp above. + * So need to wait it. + */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);