tpm: fix a kernel memory leak in tpm-sysfs.c

BugLink: http://bugs.launchpad.net/bugs/1710646

commit 13b47cfc upstream.

While cleaning up sysfs callback that prints EK we discovered a kernel
memory leak. This commit fixes the issue by zeroing the buffer used for
TPM command/response.

The leak happen when we use either tpm_vtpm_proxy, tpm_ibmvtpm or
xen-tpmfront.

Fixes: 08837438 ("TPM: sysfs functions consolidation")
Reported-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Tested-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/char/tpm/tpm-sysfs.c

@@ -38,6 +38,8 @@ static ssize_t pubek_show(struct device *dev, struct device_attribute *attr,
 
 	struct tpm_chip *chip = dev_get_drvdata(dev);
 
+	memset(&tpm_cmd, 0, sizeof(tpm_cmd));
+
 	tpm_cmd.header.in = tpm_readpubek_header;
 	err = tpm_transmit_cmd(chip, &tpm_cmd, READ_PUBEK_RESULT_SIZE, 0,
 			       "attempting to read the PUBEK");