[PATCH 4.15 008/122] tpm: st33zp24: fix potential buffer overruns caused by bit glitches on the bus

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

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

From: Jeremy Boone <jeremy.boone@xxxxxxxxxxxxxx>

commit 6d24cd186d9fead3722108dec1b1c993354645ff 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@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: James Morris <james.morris@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/char/tpm/st33zp24/st33zp24.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/char/tpm/st33zp24/st33zp24.c
+++ b/drivers/char/tpm/st33zp24/st33zp24.c
@@ -457,7 +457,7 @@ static int st33zp24_recv(struct tpm_chip
 			    size_t count)
 {
 	int size = 0;
-	int expected;
+	u32 expected;
 
 	if (!chip)
 		return -EBUSY;
@@ -474,7 +474,7 @@ static int st33zp24_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;
 	}