virtio_blk: avoid DMA to stack for the sense buffer

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@lst.de>
Cc: stable@vger.kernel.org # v4.9+
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 5545a679abd8..3c3b8f601469 100644
--- 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 virtqueue *vq,
         }
 
         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;