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    Subject[PATCH 4.14 118/222] xen/blkfront: avoid NULL blkfront_info dereference on device removal
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Vasilis Liaskovitis <vliaskovitis@suse.com>

    commit f92898e7f32e3533bfd95be174044bc349d416ca upstream.

    If a block device is hot-added when we are out of grants,
    gnttab_grant_foreign_access fails with -ENOSPC (log message "28
    granting access to ring page") in this code path:

    talk_to_blkback ->
    setup_blkring ->
    xenbus_grant_ring ->
    gnttab_grant_foreign_access

    and the failing path in talk_to_blkback sets the driver_data to NULL:

    destroy_blkring:
    blkif_free(info, 0);

    mutex_lock(&blkfront_mutex);
    free_info(info);
    mutex_unlock(&blkfront_mutex);

    dev_set_drvdata(&dev->dev, NULL);

    This results in a NULL pointer BUG when blkfront_remove and blkif_free
    try to access the failing device's NULL struct blkfront_info.

    Cc: stable@vger.kernel.org # 4.5 and later
    Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
    Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/block/xen-blkfront.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/drivers/block/xen-blkfront.c
    +++ b/drivers/block/xen-blkfront.c
    @@ -2471,6 +2471,9 @@ static int blkfront_remove(struct xenbus

    dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);

    + if (!info)
    + return 0;
    +
    blkif_free(info, 0);

    mutex_lock(&info->mutex);

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