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[Qemu-devel] [PATCH] usb-linux.c: fix buffer overflow

From: Jim Paris
Subject: [Qemu-devel] [PATCH] usb-linux.c: fix buffer overflow
Date: Mon, 24 Aug 2009 17:14:57 -0400
User-agent: Mutt/1.5.18 (2008-05-17)

From 0865ed67a30a1bde463a8db2baab8b6dbb0fcff5 Mon Sep 17 00:00:00 2001
From: Jim Paris <address@hidden>
Date: Mon, 24 Aug 2009 14:56:12 -0400
Subject: [PATCH] usb-linux.c: fix buffer overflow

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:

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 <address@hidden>

Increasing the buffer to 2048 is all that's necessary to fix the
original bug report.  It might make sense to increase the buffer size
more (hw/usb-musb.c has some comments about 32k buffers).

I don't understand all of the USB code too well, so the rest of the
patch might not be optimal -- maybe it's OK to just cap the length
before we pass it to the kernel, and then let async_complete_control
notice that the transferred length was less than requested, 
rather than failing the request completely?

 usb-linux.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/usb-linux.c b/usb-linux.c
index 043f6b6..eb1c5f0 100644
--- a/usb-linux.c
+++ b/usb-linux.c
@@ -115,7 +115,7 @@ struct ctrl_struct {
     uint16_t offset;
     uint8_t  state;
     struct   usb_ctrlrequest req;
-    uint8_t  buffer[1024];
+    uint8_t  buffer[2048];
 typedef struct USBHostDevice {
@@ -552,6 +552,7 @@ 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.
@@ -580,6 +581,13 @@ 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 (%u > %lu)\n",
+                   buffer_len, sizeof(s->ctrl.buffer));
+           return USB_RET_STALL;
+    }
     aurb = async_alloc();
     aurb->hdev   = s;
     aurb->packet = p;
@@ -596,7 +604,7 @@ 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;

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