In tftp_read we send a request for a new packet without checking if we
have enough space in the FIFO. This can lead to a FIFO overflow and a
corrupt file. Add a check for it.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>