s390/zcrypt: do not retry administrative requests

All kind of administrative requests should not been retried. Some card
firmware detects this and assumes a replay attack. This patch checks
on failure if the low level functions indicate a retry (EAGAIN) and
checks for the ADMIN flag set on the request message.  If this both
are true, the response code for this message is changed to EIO to make
sure the zcrypt API layer does not attempt to retry the request. As of
now the ADMIN flag is set for a request message when
- for EP11 the field 'flags' of the EP11 CPRB struct has the leftmost
  bit set.
- for CCA when the CPRB minor version is 'T3', 'T5', 'T6' or 'T7'.

Please note that the do-not-retry only applies to a request
which has been sent to the card (= has been successfully enqueued) but
the reply indicates some kind of failure and by default it would be
replied. It is totally fine to retry a request if a previous attempt
to enqueue the msg into the firmware queue had some kind of failure
and thus the card has never seen this request.

Reported-by: Frank Uhlig <Frank.Uhlig1@ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/s390/crypto/zcrypt_msgtype6.c b/drivers/s390/crypto/zcrypt_msgtype6.c
index ce71aa54f1f0..67fd2ec9c5a1 100644
--- a/drivers/s390/crypto/zcrypt_msgtype6.c
+++ b/drivers/s390/crypto/zcrypt_msgtype6.c
@@ -1133,6 +1133,9 @@ static long zcrypt_msgtype6_send_cprb(bool userspace, struct zcrypt_queue *zq,
 		ap_cancel_message(zq->queue, ap_msg);
 	}
 
+	if (rc == -EAGAIN && ap_msg->flags & AP_MSG_FLAG_ADMIN)
+		rc = -EIO; /* do not retry administrative requests */
+
 out:
 	if (rc)
 		ZCRYPT_DBF_DBG("%s send cprb at dev=%02x.%04x rc=%d\n",
@@ -1253,6 +1256,9 @@ static long zcrypt_msgtype6_send_ep11_cprb(bool userspace, struct zcrypt_queue *
 		ap_cancel_message(zq->queue, ap_msg);
 	}
 
+	if (rc == -EAGAIN && ap_msg->flags & AP_MSG_FLAG_ADMIN)
+		rc = -EIO; /* do not retry administrative requests */
+
 out:
 	if (rc)
 		ZCRYPT_DBF_DBG("%s send cprb at dev=%02x.%04x rc=%d\n",