net/l2tp: Fix reference count leak in l2tp_udp_recv_core

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.

Fix this issue by decrease the reference count before jumping to the
label invalid.

Fixes: 4522a70db7aa ("l2tp: fix reading optional fields of L2TPv3")
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Xiong <xiongx18@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 53486b1..93271a2 100644 (file)
--- 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;
+       }
 
        l2tp_recv_common(session, skb, ptr, optr, hdrflags, length);
        l2tp_session_dec_refcount(session);