[PATCH 4.9 064/120] virtio_blk: avoid DMA to stack for the sense buffer

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <hch@xxxxxx>

commit a14d749fcebe97ddf6af6db3d1f6ece85c9ddcb9 upstream.

Most users of BLOCK_PC requests allocate the sense buffer on the stack,
so to avoid DMA to the stack copy them to a field in the heap allocated
virtblk_req structure.  Without that any attempt at SCSI passthrough I/O,
including the SG_IO ioctl from userspace will crash the kernel.  Note that
this includes running tools like hdparm even when the host does not have
SCSI passthrough enabled.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/block/virtio_blk.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -56,6 +56,7 @@ struct virtblk_req {
 	struct virtio_blk_outhdr out_hdr;
 	struct virtio_scsi_inhdr in_hdr;
 	u8 status;
+	u8 sense[SCSI_SENSE_BUFFERSIZE];
 	struct scatterlist sg[];
 };
 
@@ -102,7 +103,8 @@ static int __virtblk_add_req(struct virt
 	}
 
 	if (type == cpu_to_virtio32(vq->vdev, VIRTIO_BLK_T_SCSI_CMD)) {
-		sg_init_one(&sense, vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
+		memcpy(vbr->sense, vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
+		sg_init_one(&sense, vbr->sense, SCSI_SENSE_BUFFERSIZE);
 		sgs[num_out + num_in++] = &sense;
 		sg_init_one(&inhdr, &vbr->in_hdr, sizeof(vbr->in_hdr));
 		sgs[num_out + num_in++] = &inhdr;