usb: ensure RX buffers are a multiple of the packet size

When performing an OUT transfer which is not a multiple of the
max packet size, the last packet of the OUT transfer should be
a short packet. However, there's no guarantee the host sends
the expected amount of data in the final packet.

The DWC2 USB controller handles this case by accepting any size
packet and copying it out to memory. So if the packet is bigger
than expected, it'll overrun the caller's buffer and Bad Things
will happen.

The USB 2.0 spec seems to endorse this behavior. Section 8.5.1
says "an ACK handshake indicates the endpoint has space for a
wMaxPacketSize data payload." So it is possible that other USB
controllers share the DWC2's behavior.

The simplest solution is to force all USB RX buffers to be big
enough to hold the transfer size, rounded up to a multiple of
the max packet size. For example, a transfer of 700 bytes would
require a 1024-byte buffer if the MPS = 512 bytes.

Change-Id: Ibb84d2b2d53aec8800a3a7c2449f7a17480acbcf

0 files changed, 0 insertions, 0 deletions