net/l2tp: Fix reference count leak in l2tp_udp_recv_core

commit 9b6ff7eb666415e1558f1ba8a742f5db6a9954de upstream.

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: 7ad9ead2b558 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 95805a6331be207d78acc88c0a564b573adb29c3..421b2c89ce12a1b64959a5fc1f552461b630f107 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -886,8 +886,10 @@ 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 error;
+       }
 
        l2tp_recv_common(session, skb, ptr, optr, hdrflags, length);
        l2tp_session_dec_refcount(session);