[PATCH] hw/usb/canokey: Fix buffer overflow for OUT packet

[Hongren Zheng]

When USBPacket in OUT direction has larger payload
than the ep_out_buffer (of size 512), a buffer overflow
would occur.

It could be fixed by limiting the size of usb_packet_copy
to be at most buffer size. Further optimization gets rid
of the ep_out_buffer and directly uses ep_out as the target
buffer.

This is reported by a security researcher who artificially
constructed an OUT packet of size 2047. The report has gone
through the QEMU security process, and as this device is for
testing purpose and no deployment of it in virtualization
environment is observed, it is triaged not to be a security bug.

Reported-by: Juan Jose Lopez Jaimez <thatjiaozi@gmail.com>
Signed-off-by: Hongren Zheng <i@zenithal.me>
---
 hw/usb/canokey.c | 6 +++---
 hw/usb/canokey.h | 4 ----
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/hw/usb/canokey.c b/hw/usb/canokey.c
index fae212f053..e2d66179e0 100644
--- a/hw/usb/canokey.c
+++ b/hw/usb/canokey.c
@@ -197,8 +197,8 @@ static void canokey_handle_data(USBDevice *dev, USBPacket 
*p)
     switch (p->pid) {
     case USB_TOKEN_OUT:
         trace_canokey_handle_data_out(ep_out, p->iov.size);
-        usb_packet_copy(p, key->ep_out_buffer[ep_out], p->iov.size);
         out_pos = 0;
+        /* segment packet into (possibly multiple) ep_out */
         while (out_pos != p->iov.size) {
             /*
              * key->ep_out[ep_out] set by prepare_receive
@@ -207,8 +207,8 @@ static void canokey_handle_data(USBDevice *dev, USBPacket 
*p)
              * to be the buffer length
              */
             out_len = MIN(p->iov.size - out_pos, key->ep_out_size[ep_out]);
-            memcpy(key->ep_out[ep_out],
-                    key->ep_out_buffer[ep_out] + out_pos, out_len);
+            /* usb_packet_copy would update the pos offset internally */
+            usb_packet_copy(p, key->ep_out[ep_out], out_len);
             out_pos += out_len;
             /* update ep_out_size to actual len */
             key->ep_out_size[ep_out] = out_len;
diff --git a/hw/usb/canokey.h b/hw/usb/canokey.h
index e528889d33..1b60d73485 100644
--- a/hw/usb/canokey.h
+++ b/hw/usb/canokey.h
@@ -24,8 +24,6 @@
 #define CANOKEY_EP_NUM 3
 /* BULK/INTR IN can be up to 1352 bytes, e.g. get key info */
 #define CANOKEY_EP_IN_BUFFER_SIZE 2048
-/* BULK OUT can be up to 270 bytes, e.g. PIV import cert */
-#define CANOKEY_EP_OUT_BUFFER_SIZE 512
 
 typedef enum {
     CANOKEY_EP_IN_WAIT,
@@ -59,8 +57,6 @@ typedef struct CanoKeyState {
     /* OUT pointer to canokey recv buffer */
     uint8_t *ep_out[CANOKEY_EP_NUM];
     uint32_t ep_out_size[CANOKEY_EP_NUM];
-    /* For large BULK OUT, multiple write to ep_out is needed */
-    uint8_t ep_out_buffer[CANOKEY_EP_NUM][CANOKEY_EP_OUT_BUFFER_SIZE];
 
     /* Properties */
     char *file; /* canokey-file */
-- 
2.47.1