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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>,
        "Jeremy Boone" <jeremy.boone@nccgroup.trust>,
        "James Bottomley" <James.Bottomley@HansenPartnership.com>,
        "James Morris" <james.morris@microsoft.com>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.543120086@decadent.org.uk>
Subject: [PATCH 3.16 296/410] tpm_i2c_nuvoton: fix potential buffer
 overruns caused by bit glitches on the bus
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jeremy Boone <jeremy.boone@nccgroup.trust>

commit f9d4d9b5a5ef2f017bc344fb65a58a902517173b upstream.

Discrete TPMs are often connected over slow serial buses which, on
some platforms, can have glitches causing bit flips.  In all the
driver _recv() functions, we need to use a u32 to unmarshal the
response size, otherwise a bit flip of the 31st bit would cause the
expected variable to go negative, which would then try to read a huge
amount of data.  Also sanity check that the expected amount of data is
large enough for the TPM header.

Signed-off-by: Jeremy Boone <jeremy.boone@nccgroup.trust>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: James Morris <james.morris@microsoft.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/char/tpm/tpm_i2c_nuvoton.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/char/tpm/tpm_i2c_nuvoton.c
+++ b/drivers/char/tpm/tpm_i2c_nuvoton.c
@@ -267,7 +267,11 @@ static int i2c_nuvoton_recv(struct tpm_c
 	struct device *dev = chip->dev;
 	struct i2c_client *client = to_i2c_client(dev);
 	s32 rc;
-	int expected, status, burst_count, retries, size = 0;
+	int status;
+	int burst_count;
+	int retries;
+	int size = 0;
+	u32 expected;
 
 	if (count < TPM_HEADER_SIZE) {
 		i2c_nuvoton_ready(chip);    /* return to idle */
@@ -309,7 +313,7 @@ static int i2c_nuvoton_recv(struct tpm_c
 		 * to machine native
 		 */
 		expected = be32_to_cpu(*(__be32 *) (buf + 2));
-		if (expected > count) {
+		if (expected > count || expected < size) {
 			dev_err(dev, "%s() expected > count\n", __func__);
 			size = -EIO;
 			continue;