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SubjectRe: [PATCH 03/13] ACPI/IPMI: Fix race caused by the unprotected ACPI IPMI transfers
Date
On Tuesday, July 23, 2013 04:09:15 PM Lv Zheng wrote:
> This patch fixes races caused by unprotected ACPI IPMI transfers.
>
> We can see the following crashes may occur:
> 1. There is no tx_msg_lock held for iterating tx_msg_list in
> ipmi_flush_tx_msg() while it is parellel unlinked on failure in
> acpi_ipmi_space_handler() under protection of tx_msg_lock.
> 2. There is no lock held for freeing tx_msg in acpi_ipmi_space_handler()
> while it is parellel accessed in ipmi_flush_tx_msg() and
> ipmi_msg_handler().
>
> This patch enhances tx_msg_lock to protect all tx_msg accesses to solve
> this issue. Then tx_msg_lock is always held around complete() and tx_msg
> accesses.
> Calling smp_wmb() before setting msg_done flag so that messages completed
> due to flushing will not be handled as 'done' messages while their contents
> are not vaild.
>
> Signed-off-by: Lv Zheng <lv.zheng@intel.com>
> Cc: Zhao Yakui <yakui.zhao@intel.com>
> Reviewed-by: Huang Ying <ying.huang@intel.com>
> ---
> drivers/acpi/acpi_ipmi.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/acpi_ipmi.c b/drivers/acpi/acpi_ipmi.c
> index b37c189..527ee43 100644
> --- a/drivers/acpi/acpi_ipmi.c
> +++ b/drivers/acpi/acpi_ipmi.c
> @@ -230,11 +230,14 @@ static void ipmi_flush_tx_msg(struct acpi_ipmi_device *ipmi)
> struct acpi_ipmi_msg *tx_msg, *temp;
> int count = HZ / 10;
> struct pnp_dev *pnp_dev = ipmi->pnp_dev;
> + unsigned long flags;
>
> + spin_lock_irqsave(&ipmi->tx_msg_lock, flags);
> list_for_each_entry_safe(tx_msg, temp, &ipmi->tx_msg_list, head) {
> /* wake up the sleep thread on the Tx msg */
> complete(&tx_msg->tx_complete);
> }
> + spin_unlock_irqrestore(&ipmi->tx_msg_lock, flags);
>
> /* wait for about 100ms to flush the tx message list */
> while (count--) {
> @@ -268,13 +271,12 @@ static void ipmi_msg_handler(struct ipmi_recv_msg *msg, void *user_msg_data)
> break;
> }
> }
> - spin_unlock_irqrestore(&ipmi_device->tx_msg_lock, flags);
>
> if (!msg_found) {
> dev_warn(&pnp_dev->dev,
> "Unexpected response (msg id %ld) is returned.\n",
> msg->msgid);
> - goto out_msg;
> + goto out_lock;
> }
>
> /* copy the response data to Rx_data buffer */
> @@ -286,10 +288,14 @@ static void ipmi_msg_handler(struct ipmi_recv_msg *msg, void *user_msg_data)
> }
> tx_msg->rx_len = msg->msg.data_len;
> memcpy(tx_msg->data, msg->msg.data, tx_msg->rx_len);
> + /* tx_msg content must be valid before setting msg_done flag */
> + smp_wmb();

That's suspicious.

If you need the write barrier here, you'll most likely need a read barrier
somewhere else. Where's that?

> tx_msg->msg_done = 1;
>
> out_comp:
> complete(&tx_msg->tx_complete);
> +out_lock:
> + spin_unlock_irqrestore(&ipmi_device->tx_msg_lock, flags);
> out_msg:
> ipmi_free_recv_msg(msg);
> }

Rafael


--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.


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