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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Phil Elwell <phil@raspberrypi.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Mark Brown <broonie@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 370/663] spi: Skip zero-length transfers in spi_transfer_one_message()
Date:   Mon,  1 Mar 2021 17:10:18 +0100
Message-Id: <20210301161200.154477680@linuxfoundation.org>
In-Reply-To: <20210301161141.760350206@linuxfoundation.org>
References: <20210301161141.760350206@linuxfoundation.org>
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From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

[ Upstream commit b306320322c9cfaa465bc2c7367acf6072b1ac0e ]

With the introduction of 26751de25d25 ("spi: bcm2835: Micro-optimise
FIFO loops") it has become apparent that some users might initiate
zero-length SPI transfers. A fact the micro-optimization omitted, and
which turned out to cause crashes[1].

Instead of changing the micro-optimization itself, use a bigger hammer
and skip zero-length transfers altogether for drivers using the default
transfer_one_message() implementation.

Reported-by: Phil Elwell <phil@raspberrypi.com>
Fixes: 26751de25d25 ("spi: bcm2835: Micro-optimise FIFO loops")
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

[1] https://github.com/raspberrypi/linux/issues/4100
Link: https://lore.kernel.org/r/20210211180820.25757-1-nsaenzjulienne@suse.de

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/spi/spi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 7694e1ae5b0b2..4257a2d368f71 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1259,7 +1259,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 			ptp_read_system_prets(xfer->ptp_sts);
 		}
 
-		if (xfer->tx_buf || xfer->rx_buf) {
+		if ((xfer->tx_buf || xfer->rx_buf) && xfer->len) {
 			reinit_completion(&ctlr->xfer_completion);
 
 fallback_pio:
-- 
2.27.0