Re: [PATCH] net/l2tp: Fix reference count leak in l2tp_udp_recv_core
From: Tom Parkin <hidden>
Date: 2021-09-09 09:07:48
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On Thu, Sep 09, 2021 at 12:32:00 +0800, Xiyu Yang wrote:
The reference count leak issue may take place in an error handling path. If both conditions of tunnel->version == L2TP_HDR_VER_3 and the return value of l2tp_v3_ensure_opt_in_linear is nonzero, the function would directly jump to label invalid, without decrementing the reference count of the l2tp_session object session increased earlier by l2tp_tunnel_get_session(). This may result in refcount leaks.
I agree with your analysis. Thanks for catching this!
quoted hunk ↗ jump to hunk
Fix this issue by decrease the reference count before jumping to the label invalid. Signed-off-by: Xiyu Yang <redacted> Signed-off-by: Xin Xiong <redacted> Signed-off-by: Xin Tan <redacted> --- net/l2tp/l2tp_core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 53486b162f01..93271a2632b8 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c@@ -869,8 +869,10 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb) } if (tunnel->version == L2TP_HDR_VER_3 && - l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr)) + l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr)) { + l2tp_session_dec_refcount(session); goto invalid; + }
The error paths in l2tp_udp_recv_core are a bit convoluted because of the check (!session || !session->recv_skb) which may or may not need to drop a session reference if triggered. I think it could be simplified since session->recv_skb is always set for all the current session types in the tree, but doing that is probably a little patch series on its own.
l2tp_recv_common(session, skb, ptr, optr, hdrflags, length); l2tp_session_dec_refcount(session); -- 2.7.4
-- Tom Parkin Katalix Systems Ltd https://katalix.com Catalysts for your Embedded Linux software development
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