linux-kernel - [PATCH v2] spi: fsl-cpm: Check length parity before switching to 16 bit mode

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Message-ID: <3c4d81c3923c93f95ec56702a454744a4bad3cfc.1763627618.git.christophe.leroy@csgroup.eu>
Date: Thu, 20 Nov 2025 09:34:49 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Mark Brown <broonie@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"florent . trinh-thai @ cs-soprasteria . com" <florent.trinh-thai@...soprasteria.com>,
	Sverdlin Alexander <alexander.sverdlin@...mens.com>,
	stable@...r.kernel.org
Subject: [PATCH v2] spi: fsl-cpm: Check length parity before switching to 16 bit mode

Commit fc96ec826bce ("spi: fsl-cpm: Use 16 bit mode for large transfers
with even size") failed to make sure that the size is really even
before switching to 16 bit mode. Until recently the problem went
unnoticed because kernfs uses a pre-allocated bounce buffer of size
PAGE_SIZE for reading EEPROM.

But commit 8ad6249c51d0 ("eeprom: at25: convert to spi-mem API")
introduced an additional dynamically allocated bounce buffer whose size
is exactly the size of the transfer, leading to a buffer overrun in
the fsl-cpm driver when that size is odd.

Add the missing length parity verification and remain in 8 bit mode
when the length is not even.

Fixes: fc96ec826bce ("spi: fsl-cpm: Use 16 bit mode for large transfers with even size")
Cc: stable@...r.kernel.org
Closes: https://lore.kernel.org/all/638496dd-ec60-4e53-bad7-eb657f67d580@csgroup.eu/
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Reviewed-by: Sverdlin Alexander <alexander.sverdlin@...mens.com>
---
v2: Updated with comments from Alexander
---
 drivers/spi/spi-fsl-spi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
index 2f2082652a1a..481a7b28aacd 100644
--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -335,7 +335,7 @@ static int fsl_spi_prepare_message(struct spi_controller *ctlr,
 			if (t->bits_per_word == 16 || t->bits_per_word == 32)
 				t->bits_per_word = 8; /* pretend its 8 bits */
 			if (t->bits_per_word == 8 && t->len >= 256 &&
-			    (mpc8xxx_spi->flags & SPI_CPM1))
+			    !(t->len & 1) && (mpc8xxx_spi->flags & SPI_CPM1))
 				t->bits_per_word = 16;
 		}
 	}
-- 
2.49.0