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    Subject[PATCH 4.19 072/109] net: bridge: fix vlan tunnel dst refcnt when egressing
    Date
    From: Nikolay Aleksandrov <nikolay@nvidia.com>

    commit cfc579f9d89af4ada58c69b03bcaa4887840f3b3 upstream.

    The egress tunnel code uses dst_clone() and directly sets the result
    which is wrong because the entry might have 0 refcnt or be already deleted,
    causing number of problems. It also triggers the WARN_ON() in dst_hold()[1]
    when a refcnt couldn't be taken. Fix it by using dst_hold_safe() and
    checking if a reference was actually taken before setting the dst.

    [1] dmesg WARN_ON log and following refcnt errors
    WARNING: CPU: 5 PID: 38 at include/net/dst.h:230 br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge]
    Modules linked in: 8021q garp mrp bridge stp llc bonding ipv6 virtio_net
    CPU: 5 PID: 38 Comm: ksoftirqd/5 Kdump: loaded Tainted: G W 5.13.0-rc3+ #360
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014
    RIP: 0010:br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge]
    Code: e8 85 bc 01 e1 45 84 f6 74 90 45 31 f6 85 db 48 c7 c7 a0 02 19 a0 41 0f 94 c6 31 c9 31 d2 44 89 f6 e8 64 bc 01 e1 85 db 75 02 <0f> 0b 31 c9 31 d2 44 89 f6 48 c7 c7 70 02 19 a0 e8 4b bc 01 e1 49
    RSP: 0018:ffff8881003d39e8 EFLAGS: 00010246
    RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
    RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa01902a0
    RBP: ffff8881040c6700 R08: 0000000000000000 R09: 0000000000000001
    R10: 2ce93d0054fe0d00 R11: 54fe0d00000e0000 R12: ffff888109515000
    R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000401
    FS: 0000000000000000(0000) GS:ffff88822bf40000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f42ba70f030 CR3: 0000000109926000 CR4: 00000000000006e0
    Call Trace:
    br_handle_vlan+0xbc/0xca [bridge]
    __br_forward+0x23/0x164 [bridge]
    deliver_clone+0x41/0x48 [bridge]
    br_handle_frame_finish+0x36f/0x3aa [bridge]
    ? skb_dst+0x2e/0x38 [bridge]
    ? br_handle_ingress_vlan_tunnel+0x3e/0x1c8 [bridge]
    ? br_handle_frame_finish+0x3aa/0x3aa [bridge]
    br_handle_frame+0x2c3/0x377 [bridge]
    ? __skb_pull+0x33/0x51
    ? vlan_do_receive+0x4f/0x36a
    ? br_handle_frame_finish+0x3aa/0x3aa [bridge]
    __netif_receive_skb_core+0x539/0x7c6
    ? __list_del_entry_valid+0x16e/0x1c2
    __netif_receive_skb_list_core+0x6d/0xd6
    netif_receive_skb_list_internal+0x1d9/0x1fa
    gro_normal_list+0x22/0x3e
    dev_gro_receive+0x55b/0x600
    ? detach_buf_split+0x58/0x140
    napi_gro_receive+0x94/0x12e
    virtnet_poll+0x15d/0x315 [virtio_net]
    __napi_poll+0x2c/0x1c9
    net_rx_action+0xe6/0x1fb
    __do_softirq+0x115/0x2d8
    run_ksoftirqd+0x18/0x20
    smpboot_thread_fn+0x183/0x19c
    ? smpboot_unregister_percpu_thread+0x66/0x66
    kthread+0x10a/0x10f
    ? kthread_mod_delayed_work+0xb6/0xb6
    ret_from_fork+0x22/0x30
    ---[ end trace 49f61b07f775fd2b ]---
    dst_release: dst:00000000c02d677a refcnt:-1
    dst_release underflow

    Cc: stable@vger.kernel.org
    Fixes: 11538d039ac6 ("bridge: vlan dst_metadata hooks in ingress and egress paths")
    Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/bridge/br_vlan_tunnel.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/net/bridge/br_vlan_tunnel.c b/net/bridge/br_vlan_tunnel.c
    index 4d5100677c68..adb6845ceba4 100644
    --- a/net/bridge/br_vlan_tunnel.c
    +++ b/net/bridge/br_vlan_tunnel.c
    @@ -208,8 +208,8 @@ int br_handle_egress_vlan_tunnel(struct sk_buff *skb,
    return err;

    tunnel_dst = rcu_dereference(vlan->tinfo.tunnel_dst);
    - if (tunnel_dst)
    - skb_dst_set(skb, dst_clone(&tunnel_dst->dst));
    + if (tunnel_dst && dst_hold_safe(&tunnel_dst->dst))
    + skb_dst_set(skb, &tunnel_dst->dst);

    return 0;
    }
    --
    2.30.2
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