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

AlanStern · gregkh · commit 1d7d4c07932e · 2022-01-03T14:38:34.000+01:00
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@syzkaller.appspotmail.com Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/Yc+3UIQJ2STbxNua@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
@@ -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);
