[PATCH 4.19 168/168] xen/gntdev: Fix dmabuf import with non-zero sgt offset

Greg Kroah-Hartman
2020-08-17T17:20:49Z

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

commit 5fa4e6f1c2d8c9a4e47e1931b42893172d388f2b upstream.

It is possible that the scatter-gather table during dmabuf import has
non-zero offset of the data, but user-space doesn't expect that.
Fix this by failing the import, so user-space doesn't access wrong data.

Fixes: bf8dc55b1358 ("xen/gntdev: Implement dma-buf import functionality")

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200813062113.11030-2-andr2000@gmail.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/xen/gntdev-dmabuf.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/drivers/xen/gntdev-dmabuf.c
+++ b/drivers/xen/gntdev-dmabuf.c
@@ -641,6 +641,14 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_
goto fail_detach;
}

+ /* Check that we have zero offset. */
+ if (sgt->sgl->offset) {
+ ret = ERR_PTR(-EINVAL);
+ pr_debug("DMA buffer has %d bytes offset, user-space expects 0\n",
+ sgt->sgl->offset);
+ goto fail_unmap;
+ }
+
/* Check number of pages that imported buffer has. */
if (attach->dmabuf->size != gntdev_dmabuf->nr_pages << PAGE_SHIFT) {
ret = ERR_PTR(-EINVAL);