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Date: Tue, 7 Jun 2022 10:28:27 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Xiaohui Zhang <xiaohuizhang@....edu.cn> Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Xiyu Yang <xiyuyang19@...an.edu.cn>, Xin Tan <tanxin.ctf@...il.com>, Xin Xiong <xiongx18@...an.edu.cn>, Tom Parkin <tparkin@...alix.com>, netdev <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 2/2] l2tp: fix possible use-after-free On Tue, Jun 7, 2022 at 9:16 AM Xiaohui Zhang <xiaohuizhang@....edu.cn> wrote: > > We detected a suspected bug with our code clone detection tool. > > Similar to the handling of l2tp_tunnel_get in commit a622b40035d1 > ("l2ip: fix possible use-after-free"), we thought a patch might > be needed here as well. > > Before taking a refcount on a rcu protected structure, > we need to make sure the refcount is not zero. > > Signed-off-by: Xiaohui Zhang <xiaohuizhang@....edu.cn> > --- > net/l2tp/l2tp_core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c > index b759fbd09b65..c5de6d4e0818 100644 > --- a/net/l2tp/l2tp_core.c > +++ b/net/l2tp/l2tp_core.c > @@ -273,8 +273,8 @@ struct l2tp_session *l2tp_session_get(const struct net *net, u32 session_id) > > rcu_read_lock_bh(); > hlist_for_each_entry_rcu(session, session_list, global_hlist) > - if (session->session_id == session_id) { > - l2tp_session_inc_refcount(session); > + if (session->session_id == session_id && > + refcount_inc_not_zero(&session->ref_count)) { > rcu_read_unlock_bh(); > > return session; > -- > 2.17.1 > Please fix all bugs in a single patch. net/l2tp/l2tp_core.c contains four suspect calls to l2tp_session_inc_refcount()
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