ACK: [SRU][Xenial][PATCH 1/1] s390/qeth: don't clobber buffer on async TX completion

[Kleber Souza]

On 08/14/18 21:15, Joseph Salisbury wrote:
> From: Julian Wiedmann <jwi at linux.ibm.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1786057
> 
> If qeth_qdio_output_handler() detects that a transmit requires async
> completion, it replaces the pending buffer's metadata object
> (qeth_qdio_out_buffer) so that this queue buffer can be re-used while
> the data is pending completion.
> 
> Later when the CQ indicates async completion of such a metadata object,
> qeth_qdio_cq_handler() tries to free any data associated with this
> object (since HW has now completed the transfer). By calling
> qeth_clear_output_buffer(), it erronously operates on the queue buffer
> that _previously_ belonged to this transfer ... but which has been
> potentially re-used several times by now.
> This results in double-free's of the buffer's data, and failing
> transmits as the buffer descriptor is scrubbed in mid-air.
> 
> The correct way of handling this situation is to
> 1. scrub the queue buffer when it is prepared for re-use, and
> 2. later obtain the data addresses from the async-completion notifier
>    (ie. the AOB), instead of the queue buffer.
> 
> All this only affects qeth devices used for af_iucv HiperTransport.
> 
> Fixes: 0da9581ddb0f ("qeth: exploit asynchronous delivery of storage blocks")
> Signed-off-by: Julian Wiedmann <jwi at linux.ibm.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (backported from commit ce28867fd20c23cd769e78b4d619c4755bf71a1c)
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  drivers/s390/net/qeth_core.h      | 11 +++++++++++
>  drivers/s390/net/qeth_core_main.c | 22 ++++++++++++++++------
>  2 files changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
> index 50030cd..9c86ca2 100644
> --- a/drivers/s390/net/qeth_core.h
> +++ b/drivers/s390/net/qeth_core.h
> @@ -850,6 +850,17 @@ struct qeth_trap_id {
>  /*some helper functions*/
>  #define QETH_CARD_IFNAME(card) (((card)->dev)? (card)->dev->name : "")
>  
> +static inline void qeth_scrub_qdio_buffer(struct qdio_buffer *buf,
> +					  unsigned int elements)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < elements; i++)
> +		memset(&buf->element[i], 0, sizeof(struct qdio_buffer_element));
> +	buf->element[14].sflags = 0;
> +	buf->element[15].sflags = 0;
> +}
> +
>  static inline int qeth_get_micros(void)
>  {
>  	return (int) (get_tod_clock() >> 12);
> diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
> index cf2efc0..40284b4 100644
> --- a/drivers/s390/net/qeth_core_main.c
> +++ b/drivers/s390/net/qeth_core_main.c
> @@ -65,9 +65,6 @@ static void qeth_notify_skbs(struct qeth_qdio_out_q *queue,
>  		struct qeth_qdio_out_buffer *buf,
>  		enum iucv_tx_notify notification);
>  static void qeth_release_skbs(struct qeth_qdio_out_buffer *buf);
> -static void qeth_clear_output_buffer(struct qeth_qdio_out_q *queue,
> -		struct qeth_qdio_out_buffer *buf,
> -		enum qeth_qdio_buffer_states newbufstate);
>  static int qeth_init_qdio_out_buf(struct qeth_qdio_out_q *, int);
>  
>  struct workqueue_struct *qeth_wq;
> @@ -478,6 +475,7 @@ static inline void qeth_qdio_handle_aob(struct qeth_card *card,
>  	struct qaob *aob;
>  	struct qeth_qdio_out_buffer *buffer;
>  	enum iucv_tx_notify notification;
> +	unsigned int i;
>  
>  	aob = (struct qaob *) phys_to_virt(phys_aob_addr);
>  	QETH_CARD_TEXT(card, 5, "haob");
> @@ -502,10 +500,18 @@ static inline void qeth_qdio_handle_aob(struct qeth_card *card,
>  	qeth_notify_skbs(buffer->q, buffer, notification);
>  
>  	buffer->aob = NULL;
> -	qeth_clear_output_buffer(buffer->q, buffer,
> -				 QETH_QDIO_BUF_HANDLED_DELAYED);
> +	/* Free dangling allocations. The attached skbs are handled by
> +	 * qeth_cleanup_handled_pending().
> +	 */
> +	for (i = 0;
> +	     i < aob->sb_count && i < QETH_MAX_BUFFER_ELEMENTS(card);
> +	     i++) {
> +		if (aob->sba[i] && buffer->is_header[i])
> +			kmem_cache_free(qeth_core_header_cache,
> +					(void *) aob->sba[i]);
> +	}
> +	atomic_set(&buffer->state, QETH_QDIO_BUF_HANDLED_DELAYED);
>  
> -	/* from here on: do not touch buffer anymore */
>  	qdio_release_aob(aob);
>  }
>  
> @@ -3743,6 +3749,10 @@ void qeth_qdio_output_handler(struct ccw_device *ccwdev,
>  			QETH_CARD_TEXT(queue->card, 5, "aob");
>  			QETH_CARD_TEXT_(queue->card, 5, "%lx",
>  					virt_to_phys(buffer->aob));
> +
> +			/* prepare the queue slot for re-use: */
> +			qeth_scrub_qdio_buffer(buffer->buffer,
> +					       QETH_MAX_BUFFER_ELEMENTS(card));
>  			if (qeth_init_qdio_out_buf(queue, bidx)) {
>  				QETH_CARD_TEXT(card, 2, "outofbuf");
>  				qeth_schedule_recovery(card);
>