patch "USB: Fix "slab-out-of-bounds Write" bug in usb_hcd_poll_rh_status" added to usb-testing

This is a note to let you know that I've just added the patch titled

USB: Fix "slab-out-of-bounds Write" bug in usb_hcd_poll_rh_status

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the usb-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

From 1d7d4c07932e04355d6e6528d44a2f2c9e354346 Mon Sep 17 00:00:00 2001
From: Alan Stern <[email protected]>
Date: Fri, 31 Dec 2021 21:07:12 -0500
Subject: USB: Fix "slab-out-of-bounds Write" bug in usb_hcd_poll_rh_status

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.

---
 drivers/usb/core/hcd.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

index 9ffc63ae65ac..3e01dd6e509b 100644
@@ -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);

2.34.1