netdev - [BUG] net:ipv6/ip6_tunnel: A double free in ip6_tnl_start

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Message-ID: <4072c4bc.6242b.17911144f20.Coremail.lyl2019@mail.ustc.edu.cn>
Date:   Tue, 27 Apr 2021 10:06:54 +0800 (GMT+08:00)
From:   lyl2019@...l.ustc.edu.cn
To:     davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [BUG] net:ipv6/ip6_tunnel:  A double free in ip6_tnl_start_xmit

Hi, maintainer.
    Our code analyzer reported a double free bug,
and it is a little difficult for me to fix the intricate bug.

File: net/ipv6/ip6_tunnel.c

 In ip6_tnl_start_xmit, it calls ipxip6_tnl_xmit() and then
ipxip6_tnl_xmit calls ip6_tnl_xmit(). The skb could be freed
at line 1,213 via consume_skb(skb). If ip6_tnl_xmit() returns
an error code, the tx_err branch of ip6_tnl_start_xmit will free
the skb again.

Issue: e7bb18e6c8b7e ("ip6_tunnel: simplify transmit path")
Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>