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    Subject[PATCH 4.6 29/96] xenbus: dont BUG() on user mode induced condition
    Date
    4.6-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jan Beulich <JBeulich@suse.com>

    commit 0beef634b86a1350c31da5fcc2992f0d7c8a622b upstream.

    Inability to locate a user mode specified transaction ID should not
    lead to a kernel crash. For other than XS_TRANSACTION_START also
    don't issue anything to xenbus if the specified ID doesn't match that
    of any active transaction.

    Signed-off-by: Jan Beulich <jbeulich@suse.com>
    Signed-off-by: David Vrabel <david.vrabel@citrix.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/xen/xenbus/xenbus_dev_frontend.c | 14 ++++++++------
    1 file changed, 8 insertions(+), 6 deletions(-)

    --- a/drivers/xen/xenbus/xenbus_dev_frontend.c
    +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
    @@ -316,11 +316,18 @@ static int xenbus_write_transaction(unsi
    rc = -ENOMEM;
    goto out;
    }
    + } else {
    + list_for_each_entry(trans, &u->transactions, list)
    + if (trans->handle.id == u->u.msg.tx_id)
    + break;
    + if (&trans->list == &u->transactions)
    + return -ESRCH;
    }

    reply = xenbus_dev_request_and_reply(&u->u.msg);
    if (IS_ERR(reply)) {
    - kfree(trans);
    + if (msg_type == XS_TRANSACTION_START)
    + kfree(trans);
    rc = PTR_ERR(reply);
    goto out;
    }
    @@ -333,12 +340,7 @@ static int xenbus_write_transaction(unsi
    list_add(&trans->list, &u->transactions);
    }
    } else if (u->u.msg.type == XS_TRANSACTION_END) {
    - list_for_each_entry(trans, &u->transactions, list)
    - if (trans->handle.id == u->u.msg.tx_id)
    - break;
    - BUG_ON(&trans->list == &u->transactions);
    list_del(&trans->list);
    -
    kfree(trans);
    }


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