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

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Message-Id: <20200731125109.18666-2-andr2000@gmail.com>
Date:   Fri, 31 Jul 2020 15:51:04 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     xen-devel@...ts.xenproject.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, airlied@...ux.ie, daniel@...ll.ch
Cc:     sstabellini@...nel.org, dan.carpenter@...cle.com,
        intel-gfx@...ts.freedesktop.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: [PATCH 1/6] xen/gntdev: Fix dmabuf import with non-zero sgt offset

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>

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@...m.com>
---
 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