tpm: fix double write race and tpm_release free issue

Moved the atomic_set of the data_pending variable until after the
tpm_read has completed processing. The existing code had a window of
time where a second write to the driver could clobber the tpm command
buffer.

Also fixed an issue where if close was called on the tpm device before a
read completed, the tpm command buffer would be returned to the OS,
which could contain sensitive information.

Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index 36e43e50dcef..0a75638e3e56 100644
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -1171,7 +1171,7 @@ int tpm_release(struct inode *inode, struct file *file)
         flush_work_sync(&chip->work);
         file->private_data = NULL;
         atomic_set(&chip->data_pending, 0);
-        kfree(chip->data_buffer);
+        kzfree(chip->data_buffer);
         clear_bit(0, &chip->is_open);
         put_device(chip->dev);
         return 0;
@@ -1223,7 +1223,6 @@ ssize_t tpm_read(struct file *file, char __user *buf,
         del_singleshot_timer_sync(&chip->user_read_timer);
         flush_work_sync(&chip->work);
         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)
@@ -1238,6 +1237,8 @@ ssize_t tpm_read(struct file *file, char __user *buf,
                 mutex_unlock(&chip->buffer_mutex);
         }
 
+        atomic_set(&chip->data_pending, 0);
+
         return ret_size;
 }
 EXPORT_SYMBOL_GPL(tpm_read);