ALSA: compress_offload: fix remaining descriptor races in sound/core/compress_offload.c

3d3f43f ("ALSA: compress_offload: improve file descriptors
installation for dma-buf") fixed some of descriptor races in
snd_compr_task_new(), but there's a couple more left.

We need to grab the references to dmabuf before moving them into
descriptor table - trying to do that by descriptor afterwards might
end up getting a different object, with a dangling reference left in
task->{input,output}

Fixes: 3d3f43f ("ALSA: compress_offload: improve file descriptors installation for dma-buf")
Signed-off-by: Al Viro <[email protected]>
Link: https://patch.msgid.link/20241229185232.GA1977892@ZenIV
Signed-off-by: Takashi Iwai <[email protected]>

Author: Al Viro

sound/core/compress_offload.c

@@ -1053,13 +1053,13 @@ static int snd_compr_task_new(struct snd_compr_stream *stream, struct snd_compr_
 		put_unused_fd(fd_i);
 		goto cleanup;
 	}
+	/* keep dmabuf reference until freed with task free ioctl */
+	get_dma_buf(task->input);
+	get_dma_buf(task->output);
 	fd_install(fd_i, task->input->file);
 	fd_install(fd_o, task->output->file);
 	utask->input_fd = fd_i;
 	utask->output_fd = fd_o;
-	/* keep dmabuf reference until freed with task free ioctl */
-	dma_buf_get(utask->input_fd);
-	dma_buf_get(utask->output_fd);
 	list_add_tail(&task->list, &stream->runtime->tasks);
 	stream->runtime->total_tasks++;
 	return 0;