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Commit 1199f092 authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
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USB: Fix "slab-out-of-bounds Write" bug in usb_hcd_poll_rh_status 



commit 1d7d4c07932e04355d6e6528d44a2f2c9e354346 upstream.

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: default avatar <syzbot+3ae6a2b06f131ab9849f@syzkaller.appspotmail.com>
Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/Yc+3UIQJ2STbxNua@rowland.harvard.edu


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 43aac501

drivers/usb/core/hcd.c

+8 −1
Original line number Diff line number Diff line
@@ -753,6 +753,7 @@ void usb_hcd_poll_rh_status(struct usb_hcd *hcd) 
{

	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_hcd *hcd) 
		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);