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@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>

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 4704fa5..04a3e23 100644 (file)
--- 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;