linux-kernel - [PATCH 3.2 110/153] tpm_tis: fix potential buffer overruns caused by bit glitches on the bus

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Date:   Wed, 30 May 2018 11:52:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "James Bottomley" <James.Bottomley@...senPartnership.com>,
        "Jeremy Boone" <jeremy.boone@...group.trust>,
        "Jarkko Sakkinen" <jarkko.sakkinen@...ux.intel.com>,
        "James Morris" <james.morris@...rosoft.com>
Subject: [PATCH 3.2 110/153] tpm_tis: fix potential buffer overruns caused
 by bit glitches on the bus

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

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

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

commit 6bb320ca4a4a7b5b3db8c8d7250cc40002046878 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@...group.trust>
Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Signed-off-by: James Morris <james.morris@...rosoft.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/char/tpm/tpm_tis.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/char/tpm/tpm_tis.c
+++ b/drivers/char/tpm/tpm_tis.c
@@ -253,7 +253,8 @@ static int recv_data(struct tpm_chip *ch
 static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 {
 	int size = 0;
-	int expected, status;
+	int status;
+	u32 expected;
 
 	if (count < TPM_HEADER_SIZE) {
 		size = -EIO;
@@ -268,7 +269,7 @@ static int tpm_tis_recv(struct tpm_chip
 	}
 
 	expected = be32_to_cpu(*(__be32 *) (buf + 2));
-	if (expected > count) {
+	if (expected > count || expected < TPM_HEADER_SIZE) {
 		size = -EIO;
 		goto out;
 	}