[PATCH v2] vduse: prevent uninitialized memory accesses

[Maxime Coquelin]

If the VDUSE application provides a smaller config space
than the driver expects, the driver may use uninitialized
memory from the stack.

This patch prevents it by initializing the buffer passed by
the driver to store the config value.

This fix addresses CVE-2022-2308.

Cc: xieyongji@xxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # v5.15+
Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index 41c0b29739f1..35dceee3ed56 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -673,10 +673,15 @@ static void vduse_vdpa_get_config(struct vdpa_device *vdpa, unsigned int offset,
 {
 	struct vduse_dev *dev = vdpa_to_vduse(vdpa);
 
-	if (offset > dev->config_size ||
-	    len > dev->config_size - offset)
+	/* Initialize the buffer in case of partial copy. */
+	memset(buf, 0, len);
+
+	if (offset > dev->config_size)
 		return;
 
+	if (len > dev->config_size - offset)
+		len = dev->config_size - offset;
+
 	memcpy(buf, dev->config + offset, len);
 }
 
-- 
2.37.2