From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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: syzbot+3ae6a2b06f131ab9849f@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/Yc+3UIQJ2STbxNua@xxxxxxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/usb/core/hcd.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) --- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -731,6 +731,7 @@ 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? */ @@ -748,11 +749,17 @@ 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);
