linux-kernel - [PATCH v2 1/2] tpm: Fix buffer access in tpm2_get_tpm

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Date:   Fri, 13 May 2022 15:41:51 +0200
From:   Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
To:     <jarkko@...nel.org>, <linux-integrity@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <peterhuewe@....de>, <jgg@...pe.ca>, <jsnitsel@...hat.com>,
        <nayna@...ux.vnet.ibm.com>, <stefan.mahnke-hartmann@...ineon.com>,
        <alexander.steffen@...ineon.com>, <stable@...r.kernel.org>
Subject: [PATCH v2 1/2] tpm: Fix buffer access in tpm2_get_tpm_pt()

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@...r.kernel.org
Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
---
Changelog:
 * v2:
   * Add inline comment to indicate the root cause to may access unitilized
     memory.
   * Change 'field upgrade mode' to lower case.

 drivers/char/tpm/tpm2-cmd.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 4704fa553098..04a3e23a4afc 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -400,7 +400,16 @@ ssize_t tpm2_get_tpm_pt(struct tpm_chip *chip, u32 property_id,  u32 *value,
 	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;
-- 
2.25.1