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    Subject[PATCH 5.15 147/262] xen/netfront: destroy queues before real_num_tx_queues is zeroed
    Date
    From: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

    commit dcf4ff7a48e7598e6b10126cc02177abb8ae4f3f upstream.

    xennet_destroy_queues() relies on info->netdev->real_num_tx_queues to
    delete queues. Since d7dac083414eb5bb99a6d2ed53dc2c1b405224e5
    ("net-sysfs: update the queue counts in the unregistration path"),
    unregister_netdev() indirectly sets real_num_tx_queues to 0. Those two
    facts together means, that xennet_destroy_queues() called from
    xennet_remove() cannot do its job, because it's called after
    unregister_netdev(). This results in kfree-ing queues that are still
    linked in napi, which ultimately crashes:

    BUG: kernel NULL pointer dereference, address: 0000000000000000
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    PGD 0 P4D 0
    Oops: 0000 [#1] PREEMPT SMP PTI
    CPU: 1 PID: 52 Comm: xenwatch Tainted: G W 5.16.10-1.32.fc32.qubes.x86_64+ #226
    RIP: 0010:free_netdev+0xa3/0x1a0
    Code: ff 48 89 df e8 2e e9 00 00 48 8b 43 50 48 8b 08 48 8d b8 a0 fe ff ff 48 8d a9 a0 fe ff ff 49 39 c4 75 26 eb 47 e8 ed c1 66 ff <48> 8b 85 60 01 00 00 48 8d 95 60 01 00 00 48 89 ef 48 2d 60 01 00
    RSP: 0000:ffffc90000bcfd00 EFLAGS: 00010286
    RAX: 0000000000000000 RBX: ffff88800edad000 RCX: 0000000000000000
    RDX: 0000000000000001 RSI: ffffc90000bcfc30 RDI: 00000000ffffffff
    RBP: fffffffffffffea0 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000001 R12: ffff88800edad050
    R13: ffff8880065f8f88 R14: 0000000000000000 R15: ffff8880066c6680
    FS: 0000000000000000(0000) GS:ffff8880f3300000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000000000000 CR3: 00000000e998c006 CR4: 00000000003706e0
    Call Trace:
    <TASK>
    xennet_remove+0x13d/0x300 [xen_netfront]
    xenbus_dev_remove+0x6d/0xf0
    __device_release_driver+0x17a/0x240
    device_release_driver+0x24/0x30
    bus_remove_device+0xd8/0x140
    device_del+0x18b/0x410
    ? _raw_spin_unlock+0x16/0x30
    ? klist_iter_exit+0x14/0x20
    ? xenbus_dev_request_and_reply+0x80/0x80
    device_unregister+0x13/0x60
    xenbus_dev_changed+0x18e/0x1f0
    xenwatch_thread+0xc0/0x1a0
    ? do_wait_intr_irq+0xa0/0xa0
    kthread+0x16b/0x190
    ? set_kthread_struct+0x40/0x40
    ret_from_fork+0x22/0x30
    </TASK>

    Fix this by calling xennet_destroy_queues() from xennet_uninit(),
    when real_num_tx_queues is still available. This ensures that queues are
    destroyed when real_num_tx_queues is set to 0, regardless of how
    unregister_netdev() was called.

    Originally reported at
    https://github.com/QubesOS/qubes-issues/issues/7257

    Fixes: d7dac083414eb5bb9 ("net-sysfs: update the queue counts in the unregistration path")
    Cc: stable@vger.kernel.org
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/xen-netfront.c | 39 +++++++++++++++++++++++----------------
    1 file changed, 23 insertions(+), 16 deletions(-)

    --- a/drivers/net/xen-netfront.c
    +++ b/drivers/net/xen-netfront.c
    @@ -842,6 +842,28 @@ static int xennet_close(struct net_devic
    return 0;
    }

    +static void xennet_destroy_queues(struct netfront_info *info)
    +{
    + unsigned int i;
    +
    + for (i = 0; i < info->netdev->real_num_tx_queues; i++) {
    + struct netfront_queue *queue = &info->queues[i];
    +
    + if (netif_running(info->netdev))
    + napi_disable(&queue->napi);
    + netif_napi_del(&queue->napi);
    + }
    +
    + kfree(info->queues);
    + info->queues = NULL;
    +}
    +
    +static void xennet_uninit(struct net_device *dev)
    +{
    + struct netfront_info *np = netdev_priv(dev);
    + xennet_destroy_queues(np);
    +}
    +
    static void xennet_set_rx_rsp_cons(struct netfront_queue *queue, RING_IDX val)
    {
    unsigned long flags;
    @@ -1611,6 +1633,7 @@ static int xennet_xdp(struct net_device
    }

    static const struct net_device_ops xennet_netdev_ops = {
    + .ndo_uninit = xennet_uninit,
    .ndo_open = xennet_open,
    .ndo_stop = xennet_close,
    .ndo_start_xmit = xennet_start_xmit,
    @@ -2103,22 +2126,6 @@ error:
    return err;
    }

    -static void xennet_destroy_queues(struct netfront_info *info)
    -{
    - unsigned int i;
    -
    - for (i = 0; i < info->netdev->real_num_tx_queues; i++) {
    - struct netfront_queue *queue = &info->queues[i];
    -
    - if (netif_running(info->netdev))
    - napi_disable(&queue->napi);
    - netif_napi_del(&queue->napi);
    - }
    -
    - kfree(info->queues);
    - info->queues = NULL;
    -}
    -


    static int xennet_create_page_pool(struct netfront_queue *queue)

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