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    Subject[PATCH 5.10 027/122] net/l2tp: Fix reference count leak in l2tp_udp_recv_core
    Date
    From: Xiyu Yang <xiyuyang19@fudan.edu.cn>

    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: 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/l2tp/l2tp_core.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/net/l2tp/l2tp_core.c
    +++ b/net/l2tp/l2tp_core.c
    @@ -869,8 +869,10 @@ static int l2tp_udp_recv_core(struct l2t
    }

    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);

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