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"Use after free" issue appears in suspend once race occurs when
napi poll scheduls after `netif_device_detach` and before napi disables.
For details, during suspend flow of virtio-net,
the tx queue state is set to "__QUEUE_STATE_DRV_XOFF" by CPU-A.
And at some coincidental times, if a TCP connection is still working,
CPU-B does `virtnet_poll` before napi disable.
In this flow, the state "__QUEUE_STATE_DRV_XOFF"
of tx queue will be cleared. This is not the normal process it expects.
After that, CPU-A continues to close driver then virtqueue is removed.
Sequence likes below:
--------------------------------------------------------------------------
CPU-A CPU-B
----- -----
suspend is called A TCP based on
virtio-net still work
virtnet_freeze
|- virtnet_freeze_down
| |- netif_device_detach
| | |- netif_tx_stop_all_queues
| | |- netif_tx_stop_queue
| | |- set_bit
| | (__QUEUE_STATE_DRV_XOFF,...)
| | softirq rasied
| | |- net_rx_action
| | |- napi_poll
| | |- virtnet_poll
| | |- virtnet_poll_cleantx
| | |- netif_tx_wake_queue
| | |- test_and_clear_bit
| | (__QUEUE_STATE_DRV_XOFF,...)
| |- virtnet_close
| |- virtnet_disable_queue_pair
| |- virtnet_napi_tx_disable
|- remove_vq_common
--------------------------------------------------------------------------
When TCP delayack timer is up, a cpu gets softirq and irq handler
`tcp_delack_timer_handler` will be called, which will finally call
`start_xmit` in virtio net driver.
Then the access to tx virtq will cause panic.
The root cause of this issue is that napi tx
is not disable before `netif_tx_stop_queue`,
once `virnet_poll` schedules in such coincidental time,
the tx queue state will be cleared.
To solve this issue, adjusts the order of
function `virtnet_close` in `virtnet_freeze_down`.
Co-developed-by: Ying Xu <ying123.xu@samsung.com>
Signed-off-by: Ying Xu <ying123.xu@samsung.com>
Signed-off-by: Junnan Wu <junnan01.wu@samsung.com>
Message-Id: <20250812090817.3463403-1-junnan01.wu@samsung.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.