linux-kernel - [PATCH] tpm_tis: Fix undefined behavior in tpm_tis_spi_transfer

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Message-ID: <20250917153022.18567-1-gunnarku@amazon.com>
Date: Wed, 17 Sep 2025 15:29:56 +0000
From: Gunnar Kudrjavets <gunnarku@...zon.com>
To: <peterhuewe@....de>, <jarkko@...nel.org>
CC: <jgg@...pe.ca>, <kyarlagadda@...dia.com>,
	<linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Justinien
 Bouron" <jbouron@...zon.com>
Subject: [PATCH] tpm_tis: Fix undefined behavior in tpm_tis_spi_transfer_half()

When len is 0, the while loop in tpm_tis_spi_transfer_half() never
executes, leaving ret uninitialized. This will lead to undefined
behavior when the function returns.

The issue was introduced when tpm_tis_spi_transfer() was refactored
to call tpm_tis_spi_transfer_half() or tpm_tis_spi_transfer_full().
While ret is properly initialized in tpm_tis_spi_transfer_full(), it
was missed in tpm_tis_spi_transfer_half().

Initialize ret to 0 at the beginning of the function to ensure
defined behavior in all code paths.

Found by GCC 14.2.0 static analyzer with -fanalyzer.

Fixes: a86a42ac2bd6 ("tpm_tis_spi: Add hardware wait polling")
Signed-off-by: Gunnar Kudrjavets <gunnarku@...zon.com>
Reviewed-by: Justinien Bouron <jbouron@...zon.com>
---
 drivers/char/tpm/tpm_tis_spi_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm_tis_spi_main.c b/drivers/char/tpm/tpm_tis_spi_main.c
index 61b42c83ced8..1b6d79662ca1 100644
--- a/drivers/char/tpm/tpm_tis_spi_main.c
+++ b/drivers/char/tpm/tpm_tis_spi_main.c
@@ -85,7 +85,7 @@ static int tpm_tis_spi_transfer_half(struct tpm_tis_data *data,	u32 addr,
 	struct spi_transfer spi_xfer[3];
 	struct spi_message m;
 	u8 transfer_len;
-	int ret;
+	int ret = 0;

 	while (len) {
 		transfer_len = min_t(u16, len, MAX_SPI_FRAMESIZE);

base-commit: 5aca7966d2a7255ba92fd5e63268dd767b223aa5
--
2.47.3