[Xen-devel] [PATCH 05/32] usb-linux.c: fix buffer overflow

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

From: Jim Paris <jim@xxxxxxxx>

In usb-linux.c:usb_host_handle_control, we pass a 1024-byte buffer and
length to the kernel.  However, the length was provided by the caller
of dev->handle_packet, and is not checked, so the kernel might provide
too much data and overflow our buffer.

For example, hw/usb-uhci.c could set the length to 2047.
hw/usb-ohci.c looks like it might go up to 4096 or 8192.

This causes a qemu crash, as reported here:
  http://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg18447.html

This patch increases the usb-linux.c buffer size to 2048 to fix the
specific device reported, and adds a check to avoid the overflow in
any case.

Signed-off-by: Jim Paris <jim@xxxxxxxx>
Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
---
 usb-linux.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/usb-linux.c b/usb-linux.c
index 5dfed8c..51bac8a 100644
--- a/usb-linux.c
+++ b/usb-linux.c
@@ -117,7 +117,7 @@ struct ctrl_struct {
     uint16_t offset;
     uint8_t  state;
     struct   usb_ctrlrequest req;
-    uint8_t  buffer[1024];
+    uint8_t  buffer[2048];
 };
 
 typedef struct USBHostDevice {
@@ -554,6 +554,7 @@ static int usb_host_handle_control(USBHostDevice *s, 
USBPacket *p)
     struct usbdevfs_urb *urb;
     AsyncURB *aurb;
     int ret, value, index;
+    int buffer_len;
 
     /* 
      * Process certain standard device requests.
@@ -582,6 +583,13 @@ static int usb_host_handle_control(USBHostDevice *s, 
USBPacket *p)
 
     /* The rest are asynchronous */
 
+    buffer_len = 8 + s->ctrl.len;
+    if (buffer_len > sizeof(s->ctrl.buffer)) {
+           fprintf(stderr, "husb: ctrl buffer too small (%d > %zu)\n",
+                   buffer_len, sizeof(s->ctrl.buffer));
+           return USB_RET_STALL;
+    }
+
     aurb = async_alloc();
     aurb->hdev   = s;
     aurb->packet = p;
@@ -598,7 +606,7 @@ static int usb_host_handle_control(USBHostDevice *s, 
USBPacket *p)
     urb->endpoint = p->devep;
 
     urb->buffer        = &s->ctrl.req;
-    urb->buffer_length = 8 + s->ctrl.len;
+    urb->buffer_length = buffer_len;
 
     urb->usercontext = s;
 
-- 
1.7.10.4


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