NFC: digital: Add NFC-DEP Target-side NACK Support

When an NFC-DEP Target receives a NACK PDU with
a PNI equal to 1 less than the current PNI, it
is supposed to re-send the last PDU.  This is
implied in section 14.12.5.4 of the NFC Digital
Protocol Spec.

The digital layer's NFC-DEP code doesn't implement
Target-side NACK handing so add it.  The last PDU
that was sent is saved in the 'nfc_digital_dev'
structure's 'saved_skb' member.  The skb will have
an additional reference taken to ensure that the skb
isn't freed when the driver performs a kfree_skb()
on the skb.  The length of the skb/PDU is also saved
so the length can be restored when re-sending the PDU
in the skb (the driver will perform an skb_pull() so
an skb_push() needs to be done to restore the skb's
data pointer/length).

Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

1 files changed, 51 insertions, 11 deletions

diff --git a/net/nfc/digital_dep.c b/net/nfc/digital_dep.c
index 9840e858ec5b..31418edbe78e 100644
--- a/net/nfc/digital_dep.c
+++ b/net/nfc/digital_dep.c
@@ -864,14 +864,29 @@ static int digital_tg_send_ack(struct nfc_digital_dev *ddev,
 
         ddev->skb_add_crc(skb);
 
+        ddev->saved_skb = skb_get(skb);
+        ddev->saved_skb_len = skb->len;
+
         rc = digital_tg_send_cmd(ddev, skb, 1500, digital_tg_recv_dep_req,
                                  data_exch);
-        if (rc)
+        if (rc) {
                 kfree_skb(skb);
+                kfree_skb(ddev->saved_skb);
+                ddev->saved_skb = NULL;
+        }
 
         return rc;
 }
 
+static int digital_tg_send_saved_skb(struct nfc_digital_dev *ddev)
+{
+        skb_get(ddev->saved_skb);
+        skb_push(ddev->saved_skb, ddev->saved_skb_len);
+
+        return digital_tg_send_cmd(ddev, ddev->saved_skb, 1500,
+                                   digital_tg_recv_dep_req, NULL);
+}
+
 static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
                                     struct sk_buff *resp)
 {
@@ -948,6 +963,9 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
                         goto exit;
                 }
 
+                kfree_skb(ddev->saved_skb);
+                ddev->saved_skb = NULL;
+
                 resp = digital_recv_dep_data_gather(ddev, pfb, resp,
                                                     digital_tg_send_ack, NULL);
                 if (IS_ERR(resp)) {
@@ -966,23 +984,36 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
                 rc = 0;
                 break;
         case DIGITAL_NFC_DEP_PFB_ACK_NACK_PDU:
-                if (DIGITAL_NFC_DEP_PFB_PNI(pfb) != ddev->curr_nfc_dep_pni) {
-                        PROTOCOL_ERR("14.12.3.4");
-                        rc = -EIO;
-                        goto exit;
-                }
+                if (!DIGITAL_NFC_DEP_NACK_BIT_SET(pfb)) { /* ACK */
+                        if ((DIGITAL_NFC_DEP_PFB_PNI(pfb) !=
+                                                ddev->curr_nfc_dep_pni) ||
+                            !ddev->chaining_skb || !ddev->saved_skb) {
+                                rc = -EIO;
+                                goto exit;
+                        }
+
+                        kfree_skb(ddev->saved_skb);
+                        ddev->saved_skb = NULL;
 
-                if (ddev->chaining_skb && !DIGITAL_NFC_DEP_NACK_BIT_SET(pfb)) {
                         rc = digital_tg_send_dep_res(ddev, ddev->chaining_skb);
                         if (rc)
                                 goto exit;
+                } else { /* NACK */
+                        if ((DIGITAL_NFC_DEP_PFB_PNI(pfb + 1) !=
+                                                ddev->curr_nfc_dep_pni) ||
+                            !ddev->saved_skb) {
+                                rc = -EIO;
+                                goto exit;
+                        }
 
-                        return;
+                        rc = digital_tg_send_saved_skb(ddev);
+                        if (rc) {
+                                kfree_skb(ddev->saved_skb);
+                                goto exit;
+                        }
                 }
 
-                pr_err("Received a ACK/NACK PDU\n");
-                rc = -EINVAL;
-                goto exit;
+                return;
         case DIGITAL_NFC_DEP_PFB_SUPERVISOR_PDU:
                 pr_err("Received a SUPERVISOR PDU\n");
                 rc = -EINVAL;
@@ -995,6 +1026,9 @@ exit:
         kfree_skb(ddev->chaining_skb);
         ddev->chaining_skb = NULL;
 
+        kfree_skb(ddev->saved_skb);
+        ddev->saved_skb = NULL;
+
         if (rc)
                 kfree_skb(resp);
 }
@@ -1033,6 +1067,9 @@ int digital_tg_send_dep_res(struct nfc_digital_dev *ddev, struct sk_buff *skb)
 
         ddev->skb_add_crc(tmp_skb);
 
+        ddev->saved_skb = skb_get(tmp_skb);
+        ddev->saved_skb_len = tmp_skb->len;
+
         rc = digital_tg_send_cmd(ddev, tmp_skb, 1500, digital_tg_recv_dep_req,
                                  NULL);
         if (rc) {
@@ -1041,6 +1078,9 @@ int digital_tg_send_dep_res(struct nfc_digital_dev *ddev, struct sk_buff *skb)
 
                 kfree_skb(chaining_skb);
                 ddev->chaining_skb = NULL;
+
+                kfree_skb(ddev->saved_skb);
+                ddev->saved_skb = NULL;
         }
 
         return rc;