TPM: Zero buffer whole after copying to userspace

commit 3ab1aff89477dafb1aaeafe8c8669114a02b7226 upstream.

Commit 3321c07ae5068568cd61ac9f4ba749006a7185c9 correctly clears the TPM
buffer if the user specified read length is >= the TPM buffer length. However,
if the user specified read length is < the TPM buffer length, then part of the
TPM buffer is left uncleared.

Reported-by: Seth Forshee <seth.forshee@canonical.com>
Cc: Debora Velarde <debora@linux.vnet.ibm.com>
Cc: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
Cc: Marcel Selhorst <m.selhorst@sirrix.com>
Cc: tpmdd-devel@lists.sourceforge.net
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index 361a1df..b366b34 100644 (file)
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -1115,12 +1115,13 @@ ssize_t tpm_read(struct file *file, char __user *buf,
        ret_size = atomic_read(&chip->data_pending);
        atomic_set(&chip->data_pending, 0);
        if (ret_size > 0) {     /* relay data */
        ret_size = atomic_read(&chip->data_pending);
        atomic_set(&chip->data_pending, 0);
        if (ret_size > 0) {     /* relay data */

+               ssize_t orig_ret_size = ret_size;

                if (size < ret_size)
                        ret_size = size;
 
                mutex_lock(&chip->buffer_mutex);
                rc = copy_to_user(buf, chip->data_buffer, ret_size);
                if (size < ret_size)
                        ret_size = size;
 
                mutex_lock(&chip->buffer_mutex);
                rc = copy_to_user(buf, chip->data_buffer, ret_size);

-               memset(chip->data_buffer, 0, ret_size);
+               memset(chip->data_buffer, 0, orig_ret_size);

                if (rc)
                        ret_size = -EFAULT;
 
                if (rc)
                        ret_size = -EFAULT;