From 6bb320ca4a4a7b5b3db8c8d7250cc40002046878 Mon Sep 17 00:00:00 2001
From: Jeremy Boone <jeremy.boone@nccgroup.trust>
Date: Thu, 8 Feb 2018 12:32:06 -0800
Subject: [PATCH] tpm_tis: fix potential buffer overruns caused by bit glitches
 on the bus

References: bsc#1082555
Patch-mainline: v4.16-rc4
Git-commit: 6bb320ca4a4a7b5b3db8c8d7250cc40002046878

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>
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.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>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 drivers/char/tpm/tpm_tis_core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 183a5f54d875..da074e3db19b 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -270,7 +270,8 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 {
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
 	int size = 0;
-	int expected, status;
+	int status;
+	u32 expected;
 
 	if (count < TPM_HEADER_SIZE) {
 		size = -EIO;
@@ -285,7 +286,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 	}
 
 	expected = be32_to_cpu(*(__be32 *) (buf + 2));
-	if (expected > count) {
+	if (expected > count || expected < TPM_HEADER_SIZE) {
 		size = -EIO;
 		goto out;
 	}
-- 
2.13.6