[PATCH 5.4 29/34] tpm: Fix buffer access in tpm2_get_tpm_pt()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@infineon.com>

commit e57b2523bd37e6434f4e64c7a685e3715ad21e9a upstream.

Under certain conditions uninitialized memory will be accessed.
As described by TCG Trusted Platform Module Library Specification,
rev. 1.59 (Part 3: Commands), if a TPM2_GetCapability is received,
requesting a capability, the TPM in field upgrade mode may return a
zero length list.
Check the property count in tpm2_get_tpm_pt().

Fixes: 2ab3241161b3 ("tpm: migrate tpm2_get_tpm_pt() to use struct tpm_buf")
Cc: stable@vger.kernel.org
Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@infineon.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/char/tpm/tpm2-cmd.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -706,7 +706,16 @@ ssize_t tpm2_get_tpm_pt(struct tpm_chip
 	if (!rc) {
 		out = (struct tpm2_get_cap_out *)
 			&buf.data[TPM_HEADER_SIZE];
-		*value = be32_to_cpu(out->value);
+		/*
+		 * To prevent failing boot up of some systems, Infineon TPM2.0
+		 * returns SUCCESS on TPM2_Startup in field upgrade mode. Also
+		 * the TPM2_Getcapability command returns a zero length list
+		 * in field upgrade mode.
+		 */
+		if (be32_to_cpu(out->property_cnt) > 0)
+			*value = be32_to_cpu(out->value);
+		else
+			rc = -ENODATA;
 	}
 	tpm_buf_destroy(&buf);
 	return rc;