[PATCH 3.16 214/366] s390/qeth: don't clobber buffer on async TX completion

Ben Hutchings
2018-11-11T20:06:50Z

From: Julian Wiedmann <jwi@linux.ibm.com>

commit ce28867fd20c23cd769e78b4d619c4755bf71a1c upstream.

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@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/s390/net/qeth_core.h | 11 +++++++++++
drivers/s390/net/qeth_core_main.c | 22 ++++++++++++++++------
2 files changed, 27 insertions(+), 6 deletions(-)

--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -844,6 +844,17 @@ 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 struct qeth_card *CARD_FROM_CDEV(struct ccw_device *cdev)
{
struct qeth_card *card = dev_get_drvdata(&((struct ccwgroup_device *)
--- 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
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;
@@ -451,6 +448,7 @@ static inline void qeth_qdio_handle_aob(
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");
@@ -475,10 +473,18 @@ static inline void qeth_qdio_handle_aob(
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);
}

@@ -3635,6 +3641,10 @@ void qeth_qdio_output_handler(struct ccw
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);