netdev - Re: [PATCH net-next] ip_tunnel: Fix DST_METADATA dst_entry handle in tnl_update

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Date:   Sat, 16 Feb 2019 08:34:27 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     wenxu@...oud.cn
Cc:     "David S. Miller" <davem@...emloft.net>, rong.a.chen@...el.com,
        Network Development <netdev@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, LKP <lkp@...org>
Subject: Re: [PATCH net-next] ip_tunnel: Fix DST_METADATA dst_entry handle in tnl_update_pmtu

On Sat, Feb 16, 2019 at 2:11 AM <wenxu@...oud.cn> wrote:
>
> From: wenxu <wenxu@...oud.cn>
>
> BUG report in selftests: bpf: test_tunnel.sh
>
> Testing IPIP tunnel...
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> PGD 0 P4D 0
> Oops: 0010 [#1] SMP PTI
> CPU: 0 PID: 16822 Comm: ping Not tainted 5.0.0-rc3-00352-gc8b34e6 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> RIP: 0010:          (null)
> Code: Bad RIP value.
> RSP: 0018:ffffc9000104f9c8 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: ffffe8ffffc071a8 RCX: 0000000000000000
> RDX: ffff888054e33000 RSI: ffff88807796f500 RDI: ffffe8ffffc07130
> RBP: ffff88807796f500 R08: ffff88806da4f0a0 R09: 0000000000000000
> R10: 0000000000000004 R11: ffff888054e33000 R12: 0000000000000054
> R13: ffff88805e714000 R14: ffff88806da4f0a0 R15: 0000000000000000
> FS:  00007f4c00431500(0000) GS:ffff88813fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffffffffd6 CR3: 000000008276e000 CR4: 00000000000406f0
> Call Trace:
>  ? tnl_update_pmtu+0x21b/0x250 [ip_tunnel]
>  ? ip_md_tunnel_xmit+0x1b7/0xdc0 [ip_tunnel]
>  ? ipip_tunnel_xmit+0x90/0xc0 [ipip]
>  ? dev_hard_start_xmit+0x98/0x210
>  ? __dev_queue_xmit+0x6a9/0x8e0
>
> The bpf program set tunnel_key through bpf_skb_set_tunnel_key which will
> drop the old dst_entry and create a DST_METADATA dst_entry. It will lead
> the tunnel_update_pmtu operator the dst_entry incorrect. So It should be
> check the dst_entry is valid.
>
> Fixes: c8b34e680a09 ("ip_tunnel: Add tnl_update_pmtu in ip_md_tunnel_xmit")
> Signed-off-by: wenxu <wenxu@...oud.cn>

different fix for this issue was sent earlier:
https://patchwork.ozlabs.org/patch/1042687/
I think it's more complete than this one.