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net/l2tp: Fix reference count leak in l2tp_udp_recv_core

Guillaume Nault requested to merge gnault/centos-stream-9:bz2023271 into main

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2023271 Upstream Status: linux.git

commit 9b6ff7eb666415e1558f1ba8a742f5db6a9954de Author: Xiyu Yang xiyuyang19@fudan.edu.cn Date: Thu Sep 9 12:32:00 2021 +0800

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>

Signed-off-by: Guillaume Nault gnault@redhat.com

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