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    Subject[PATCH 5.15 168/279] NFC: reorganize the functions in nci_request
    Date
    From: Lin Ma <linma@zju.edu.cn>

    [ Upstream commit 86cdf8e38792545161dbe3350a7eced558ba4d15 ]

    There is a possible data race as shown below:

    thread-A in nci_request() | thread-B in nci_close_device()
    | mutex_lock(&ndev->req_lock);
    test_bit(NCI_UP, &ndev->flags); |
    ... | test_and_clear_bit(NCI_UP, &ndev->flags)
    mutex_lock(&ndev->req_lock); |
    |

    This race will allow __nci_request() to be awaked while the device is
    getting removed.

    Similar to commit e2cb6b891ad2 ("bluetooth: eliminate the potential race
    condition when removing the HCI controller"). this patch alters the
    function sequence in nci_request() to prevent the data races between the
    nci_close_device().

    Signed-off-by: Lin Ma <linma@zju.edu.cn>
    Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")
    Link: https://lore.kernel.org/r/20211115145600.8320-1-linma@zju.edu.cn
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/nfc/nci/core.c | 11 +++++++----
    1 file changed, 7 insertions(+), 4 deletions(-)

    diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
    index 82ab39d80726e..39994dbb6a55b 100644
    --- a/net/nfc/nci/core.c
    +++ b/net/nfc/nci/core.c
    @@ -144,12 +144,15 @@ inline int nci_request(struct nci_dev *ndev,
    {
    int rc;

    - if (!test_bit(NCI_UP, &ndev->flags))
    - return -ENETDOWN;
    -
    /* Serialize all requests */
    mutex_lock(&ndev->req_lock);
    - rc = __nci_request(ndev, req, opt, timeout);
    + /* check the state after obtaing the lock against any races
    + * from nci_close_device when the device gets removed.
    + */
    + if (test_bit(NCI_UP, &ndev->flags))
    + rc = __nci_request(ndev, req, opt, timeout);
    + else
    + rc = -ENETDOWN;
    mutex_unlock(&ndev->req_lock);

    return rc;
    --
    2.33.0


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