When the USB core code for getting root-hub status reports was
originally written, it was assumed that the hub driver would be its
only caller. But this isn't true now; user programs can use usbfs to
communicate with root hubs and get status reports. When they do this,
they may use a transfer_buffer that is smaller than the data returned
by the HCD, which will lead to a buffer overflow error when
usb_hcd_poll_rh_status() tries to store the status data. This was
discovered by syzbot:
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline]
BUG: KASAN: slab-out-of-bounds in usb_hcd_poll_rh_status+0x5f4/0x780 drivers/usb/core/hcd.c:776
Write of size 2 at addr ffff88801da403c0 by task syz-executor133/4062
This patch fixes the bug by reducing the amount of status data if it
won't fit in the transfer_buffer. If some data gets discarded then
the URB's completion status is set to -EOVERFLOW rather than 0, to let
the user know what happened.
Reported-and-tested-by: syzbot+3ae6a2b06f131ab9849f@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
[as1966]
drivers/usb/core/hcd.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
Index: usb-devel/drivers/usb/core/hcd.c
===================================================================
--- usb-devel.orig/drivers/usb/core/hcd.c
+++ usb-devel/drivers/usb/core/hcd.c
@@ -753,6 +753,7 @@ void usb_hcd_poll_rh_status(struct usb_h
{
struct urb *urb;
int length;
+ int status;
unsigned long flags;
char buffer[6]; /* Any root hubs with > 31 ports? */
@@ -770,11 +771,17 @@ void usb_hcd_poll_rh_status(struct usb_h
if (urb) {
clear_bit(HCD_FLAG_POLL_PENDING, &hcd->flags);
hcd->status_urb = NULL;
+ if (urb->transfer_buffer_length >= length) {
+ status = 0;
+ } else {
+ status = -EOVERFLOW;
+ length = urb->transfer_buffer_length;
+ }
urb->actual_length = length;
memcpy(urb->transfer_buffer, buffer, length);
usb_hcd_unlink_urb_from_ep(hcd, urb);
- usb_hcd_giveback_urb(hcd, urb, 0);
+ usb_hcd_giveback_urb(hcd, urb, status);
} else {
length = 0;
set_bit(HCD_FLAG_POLL_PENDING, &hcd->flags);
