From: Chris Lesiak <chris.lesiak@licor.com>
Date: Thu, 7 Mar 2019 20:39:00 +0000 (+0000)
Subject: spi: Fix zero length xfer bug
X-Git-Tag: v5.0.20~11
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0d6932a68e1e8f2c867c728ab99c1917b0ee8949;p=thirdparty%2Fkernel%2Fstable.git

spi: Fix zero length xfer bug

[ Upstream commit 5442dcaa0d90fc376bdfc179a018931a8f43dea4 ]

This fixes a bug for messages containing both zero length and
unidirectional xfers.

The function spi_map_msg will allocate dummy tx and/or rx buffers
for use with unidirectional transfers when the hardware can only do
a bidirectional transfer.  That dummy buffer will be used in place
of a NULL buffer even when the xfer length is 0.

Then in the function __spi_map_msg, if he hardware can dma,
the zero length xfer will have spi_map_buf called on the dummy
buffer.

Eventually, __sg_alloc_table is called and returns -EINVAL
because nents == 0.

This fix prevents the error by not using the dummy buffer when
the xfer length is zero.

Signed-off-by: Chris Lesiak <chris.lesiak@licor.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9a7def7c32370..0632a32c11055 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1024,6 +1024,8 @@ static int spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 		if (max_tx || max_rx) {
 			list_for_each_entry(xfer, &msg->transfers,
 					    transfer_list) {
+				if (!xfer->len)
+					continue;
 				if (!xfer->tx_buf)
 					xfer->tx_buf = ctlr->dummy_tx;
 				if (!xfer->rx_buf)