[PATCH 1/6] xen/gntdev: Fix dmabuf import with non-zero sgt offset

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

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: 37ccb44d0b00 ("xen/gntdev: Implement dma-buf import functionality")

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
 drivers/xen/gntdev-dmabuf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
index 75d3bb948bf3..b1b6eebafd5d 100644
--- a/drivers/xen/gntdev-dmabuf.c
+++ b/drivers/xen/gntdev-dmabuf.c
@@ -613,6 +613,14 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct 
device *dev,
                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);
-- 
2.17.1