[PATCH] virtio-blk: limit seg_max to a safe value

[Stefan Hajnoczi <stefanha@redhat.com>]

The struct virtio_blk_config seg_max value is read from the device and
incremented by 2 to account for the request header and status byte
descriptors added by the driver.

In preparation for supporting untrusted virtio-blk devices, protect
against integer overflow and limit the value to a safe maximum
(SG_MAX_SEGMENTS).

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 drivers/block/virtio_blk.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index b9fa3ef5b57c..4dfd5fc7aeea 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -728,7 +728,10 @@ static int virtblk_probe(struct virtio_device *vdev)
 	if (err || !sg_elems)
 		sg_elems = 1;
 
-	/* We need an extra sg elements at head and tail. */
+	/* Prevent integer overflows and excessive blk-mq req cmd_size */
+	sg_elems = min_t(u32, sg_elems, SG_MAX_SEGMENTS);
+
+	/* We need extra sg elements at head and tail. */
 	sg_elems += 2;
 	vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
 	if (!vblk) {
-- 
2.31.1