usb: ensure RX buffers are a multiple of the packet size

When performing an OUT transfer which is not a multiple of the
max packet size, the last packet of the OUT transfer should be
a short packet. However, there's no guarantee the host sends
the expected amount of data in the final packet.

The DWC2 USB controller handles this case by accepting any size
packet and copying it out to memory. So if the packet is bigger
than expected, it'll overrun the caller's buffer and Bad Things
will happen.

The USB 2.0 spec seems to endorse this behavior. Section 8.5.1
says "an ACK handshake indicates the endpoint has space for a
wMaxPacketSize data payload." So it is possible that other USB
controllers share the DWC2's behavior.

The simplest solution is to force all USB RX buffers to be big
enough to hold the transfer size, rounded up to a multiple of
the max packet size. For example, a transfer of 700 bytes would
require a 1024-byte buffer if the MPS = 512 bytes.

Change-Id: Ibb84d2b2d53aec8800a3a7c2449f7a17480acbcf

1 files changed, 23 insertions, 9 deletions

diff --git a/firmware/usbstack/usb_serial.c b/firmware/usbstack/usb_serial.c
index b49a5ca013..ae90b57078 100644
--- a/firmware/usbstack/usb_serial.c
+++ b/firmware/usbstack/usb_serial.c
@@ -174,7 +174,13 @@ static struct usb_endpoint_descriptor
     .bInterval        = 0
 };
 
-static struct cdc_line_coding line_coding;
+union line_coding_buffer
+{
+    struct cdc_line_coding data;
+    unsigned char raw[64];
+};
+
+static union line_coding_buffer line_coding USB_DEVBSS_ATTR;
 
 /* send_buffer: local ring buffer.
  * transit_buffer: used to store aligned data that will be sent by the USB
@@ -184,10 +190,11 @@ static struct cdc_line_coding line_coding;
  */
 #define BUFFER_SIZE 512
 #define TRANSIT_BUFFER_SIZE 32
+#define RECV_BUFFER_SIZE 32
 static unsigned char send_buffer[BUFFER_SIZE];
 static unsigned char transit_buffer[TRANSIT_BUFFER_SIZE]
     USB_DEVBSS_ATTR __attribute__((aligned(4)));
-static unsigned char receive_buffer[32]
+static unsigned char receive_buffer[512]
     USB_DEVBSS_ATTR __attribute__((aligned(32)));
 
 static void sendout(void);
@@ -293,13 +300,19 @@ bool usb_serial_control_request(struct usb_ctrlrequest* req, void* reqdata, unsi
     {
         if (req->bRequest == SET_LINE_CODING)
         {
-            if (req->wLength == sizeof(line_coding))
+            if (req->wLength == sizeof(struct cdc_line_coding))
             {
                 /* Receive line coding into local copy */
-                if(!reqdata)
-                    usb_drv_control_response(USB_CONTROL_RECEIVE, &line_coding, sizeof(line_coding));
+                if (!reqdata)
+                {
+                    usb_drv_control_response(USB_CONTROL_RECEIVE, line_coding.raw,
+                                             sizeof(struct cdc_line_coding));
+                }
                 else
+                {
                     usb_drv_control_response(USB_CONTROL_ACK, NULL, 0);
+                }
+
                 handled = true;
             }
         }
@@ -317,10 +330,11 @@ bool usb_serial_control_request(struct usb_ctrlrequest* req, void* reqdata, unsi
     {
         if (req->bRequest == GET_LINE_CODING)
         {
-            if (req->wLength == sizeof(line_coding))
+            if (req->wLength == sizeof(struct cdc_line_coding))
             {
                 /* Send back line coding so host is happy */
-                usb_drv_control_response(USB_CONTROL_ACK, &line_coding, sizeof(line_coding));
+                usb_drv_control_response(USB_CONTROL_ACK, line_coding.raw,
+                                         sizeof(struct cdc_line_coding));
                 handled = true;
             }
         }
@@ -332,7 +346,7 @@ bool usb_serial_control_request(struct usb_ctrlrequest* req, void* reqdata, unsi
 void usb_serial_init_connection(void)
 {
     /* prime rx endpoint */
-    usb_drv_recv_nonblocking(ep_out, receive_buffer, sizeof receive_buffer);
+    usb_drv_recv_nonblocking(ep_out, receive_buffer, RECV_BUFFER_SIZE);
 
     /* we come here too after a bus reset, so reset some data */
     buffer_transitlength = 0;
@@ -423,7 +437,7 @@ void usb_serial_transfer_complete(int ep,int dir, int status, int length)
             /* Data received. TODO : Do something with it ? */
 
             /* Get the next bit */
-            usb_drv_recv_nonblocking(ep_out, receive_buffer, sizeof receive_buffer);
+            usb_drv_recv_nonblocking(ep_out, receive_buffer, RECV_BUFFER_SIZE);
             break;
 
         case USB_DIR_IN: