[PATCH 13/14] usb: xhci: Fix bounce buffer overflow

[Mathias Nyman <mathias.nyman@linux.intel.com>]

From: Michal Pecio <michal.pecio@gmail.com>

High-speed devices with out of spec 1024 byte bulk endpoints exist and
are allowed by USB core, but xhci-hcd always sets packet size to 512.
The exact nature of these devices isn't documented, commit fb5ee84ea72c
("USB: Accept bulk endpoints with 1024-byte maxpacket") only states
that they "don't work with xHCI host controllers", whatever it means.

But somebody (or a malicious device) can try, and then the driver will
allocate a 512 byte bounce buffer for this endpoint and may write up to
1024 bytes into it if particular scatter-gather URBs are used, because
xhci_align_td() obtains packet size from the descriptor. Fix this.

As a side effect, TRBs will be aligned to the packet size chosen by the
driver on all endpoints of all speeds. Alignment serves the xHC, not
device, so this is fine. Only out of spec devices are affected anyway.

Reported-by: co+fd80bc5967eb22c3@bugs.sh
Link: https://lore.kernel.org/linux-usb/D4tcSGerkYkIV1DmaUo1t8TaR5qQElDLkidn@bugs.sh/
Fixes: f9c589e142d0 ("xhci: TD-fragment, align the unsplittable case with a bounce buffer")
Cc: stable@vger.kernel.org
Signed-off-by: Michal Pecio <michal.pecio@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/usb/host/xhci-ring.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 243b1fd2b2f6..c23434001e9c 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3546,15 +3546,13 @@ static u32 xhci_td_remainder(struct xhci_hcd *xhci, int transferred,
 
 
 static int xhci_align_td(struct xhci_hcd *xhci, struct urb *urb, u32 enqd_len,
-			 u32 *trb_buff_len, struct xhci_segment *seg)
+			 u32 *trb_buff_len, struct xhci_segment *seg, u32 max_pkt)
 {
 	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
 	unsigned int unalign;
-	unsigned int max_pkt;
 	u32 new_buff_len;
 	size_t len;
 
-	max_pkt = xhci_usb_endpoint_maxp(urb->dev, urb->ep);
 	unalign = (enqd_len + *trb_buff_len) % max_pkt;
 
 	/* we got lucky, last normal TRB data on segment is packet aligned */
@@ -3699,9 +3697,8 @@ int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 		if (enqd_len + trb_buff_len < full_len) {
 			field |= TRB_CHAIN;
 			if (trb_is_link(ring->enqueue + 1)) {
-				if (xhci_align_td(xhci, urb, enqd_len,
-						  &trb_buff_len,
-						  ring->enq_seg)) {
+				if (xhci_align_td(xhci, urb, enqd_len, &trb_buff_len,
+						ring->enq_seg, ring->bounce_buf_len)) {
 					send_addr = ring->enq_seg->bounce_dma;
 					/* TD bounced at least, and last on this seg */
 					td->bounce_seg = ring->enq_seg;
-- 
2.43.0