Commit 532c8b51 authored by Al Viro's avatar Al Viro Committed by Juergen Gross
Browse files

xen: fix UAF in dmabuf_exp_from_pages() 



[dma_buf_fd() fixes; no preferences regarding the tree it goes through -
up to xen folks]

As soon as we'd inserted a file reference into descriptor table, another
thread could close it.  That's fine for the case when all we are doing is
returning that descriptor to userland (it's a race, but it's a userland
race and there's nothing the kernel can do about it).  However, if we
follow fd_install() with any kind of access to objects that would be
destroyed on close (be it the struct file itself or anything destroyed
by its ->release()), we have a UAF.

dma_buf_fd() is a combination of reserving a descriptor and fd_install().
gntdev dmabuf_exp_from_pages() calls it and then proceeds to access the
objects destroyed on close - starting with gntdev_dmabuf itself.

Fix that by doing reserving descriptor before anything else and do
fd_install() only when everything had been set up.

Fixes: a240d6e4 ("xen/gntdev: Implement dma-buf export functionality")
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Acked-by: default avatarJuergen Gross <jgross@suse.com>
Message-ID: <20250712050916.GY1880847@ZenIV>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 0df11950

drivers/xen/gntdev-dmabuf.c

+10 −18
Original line number Diff line number Diff line
@@ -357,8 +357,11 @@ struct gntdev_dmabuf_export_args { 
static int dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args)

{

	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);

	struct gntdev_dmabuf *gntdev_dmabuf;

	int ret;

	struct gntdev_dmabuf *gntdev_dmabuf __free(kfree) = NULL;

	CLASS(get_unused_fd, ret)(O_CLOEXEC);



	if (ret < 0)

		return ret;



	gntdev_dmabuf = kzalloc(sizeof(*gntdev_dmabuf), GFP_KERNEL);

	if (!gntdev_dmabuf)
@@ -383,32 +386,21 @@ static int dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args) 
	exp_info.priv = gntdev_dmabuf;



	gntdev_dmabuf->dmabuf = dma_buf_export(&exp_info);

	if (IS_ERR(gntdev_dmabuf->dmabuf)) {

		ret = PTR_ERR(gntdev_dmabuf->dmabuf);

		gntdev_dmabuf->dmabuf = NULL;

		goto fail;

	}



	ret = dma_buf_fd(gntdev_dmabuf->dmabuf, O_CLOEXEC);

	if (ret < 0)

		goto fail;

	if (IS_ERR(gntdev_dmabuf->dmabuf))

		return PTR_ERR(gntdev_dmabuf->dmabuf);



	gntdev_dmabuf->fd = ret;

	args->fd = ret;



	pr_debug("Exporting DMA buffer with fd %d\n", ret);



	get_file(gntdev_dmabuf->priv->filp);

	mutex_lock(&args->dmabuf_priv->lock);

	list_add(&gntdev_dmabuf->next, &args->dmabuf_priv->exp_list);

	mutex_unlock(&args->dmabuf_priv->lock);

	get_file(gntdev_dmabuf->priv->filp);

	return 0;



fail:

	if (gntdev_dmabuf->dmabuf)

		dma_buf_put(gntdev_dmabuf->dmabuf);

	kfree(gntdev_dmabuf);

	return ret;

	fd_install(take_fd(ret), no_free_ptr(gntdev_dmabuf)->dmabuf->file);

	return 0;

}



static struct gntdev_grant_map *