USB: gadget: Reject endpoints with 0 maxpacket value

Endpoints with a maxpacket length of 0 are probably useless.  They
can't transfer any data, and it's not at all unlikely that a UDC will
crash or hang when trying to handle a non-zero-length usb_request for
such an endpoint.  Indeed, dummy-hcd gets a divide error when trying
to calculate the remainder of a transfer length by the maxpacket
value, as discovered by the syzbot fuzzer.

Currently the gadget core does not check for endpoints having a
maxpacket value of 0.  This patch adds a check to usb_ep_enable(),
preventing such endpoints from being used.

As far as I know, none of the gadget drivers in the kernel tries to
create an endpoint with maxpacket = 0, but until now there has been
nothing to prevent userspace programs under gadgetfs or configfs from
doing it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: syzbot+8ab8bf161038a8768553@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Acked-by: Felipe Balbi <balbi@kernel.org>

Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910281052370.1485-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index 92af8dc98c3d..51fa614b4079 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -98,6 +98,17 @@ int usb_ep_enable(struct usb_ep *ep)
         if (ep->enabled)
                 goto out;
 
+        /* UDC drivers can't handle endpoints with maxpacket size 0 */
+        if (usb_endpoint_maxp(ep->desc) == 0) {
+                /*
+                 * We should log an error message here, but we can't call
+                 * dev_err() because there's no way to find the gadget
+                 * given only ep.
+                 */
+                ret = -EINVAL;
+                goto out;
+        }
+
         ret = ep->ops->enable(ep, ep->desc);
         if (ret)
                 goto out;