dma-buf: free dmabuf->name in dma_buf_release()

dma-buf name can be set via DMA_BUF_SET_NAME ioctl, but once set
it never gets freed.

Free it in dma_buf_release().

Fixes: bb2bb90304 ("dma-buf: add DMA_BUF_SET_NAME ioctls")
Reported-by: syzbot+b2098bc44728a4efb3e9@syzkaller.appspotmail.com
Cc: Greg Hackmann <ghackmann@google.com>
Cc: Chenbo Feng <fengc@google.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Chenbo Feng <fengc@google.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191227063204.5813-1-xiyou.wangcong@gmail.com

drivers/dma-buf/dma-buf.c

@@ -108,6 +108,7 @@ static int dma_buf_release(struct inode *inode, struct file *file)
 		dma_resv_fini(dmabuf->resv);
 
 	module_put(dmabuf->owner);
+	kfree(dmabuf->name);
 	kfree(dmabuf);
 	return 0;
 }