xen/blkback: Move the check for misaligned I/O once more.

The commit 976222e05ea5a9959ccf880d7a24efbf79b3c6cf

    xen/blkback: Move the check for misaligned I/O higher.

moved it a bit to high. The preq->vbdev was not set, so the
check for misaligned I/O would cause a NULL pointer derefence.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/drivers/xen/blkback/blkback.c b/drivers/xen/blkback/blkback.c
index c645c83f900b..a0d3227955c9 100644
--- a/drivers/xen/blkback/blkback.c
+++ b/drivers/xen/blkback/blkback.c
@@ -514,6 +514,7 @@ static void dispatch_rw_block_io(struct blkif_st *blkif,
         pending_req->operation = req->operation;
         pending_req->status    = BLKIF_RSP_OKAY;
         pending_req->nr_pages  = nseg;
+
         for (i = 0; i < nseg; i++) {
                 seg[i].nsec = req->u.rw.seg[i].last_sect -
                         req->u.rw.seg[i].first_sect + 1;
@@ -522,12 +523,6 @@ static void dispatch_rw_block_io(struct blkif_st *blkif,
                         goto fail_response;
                 preq.nr_sects += seg[i].nsec;
 
-                if (((int)preq.sector_number|(int)seg[i].nsec) &
-                    ((bdev_logical_block_size(preq.bdev) >> 9) - 1)) {
-                        DPRINTK("Misaligned I/O request from domain %d",
-                                blkif->domid);
-                        goto fail_response;
-                }
         }
 
         if (vbd_translate(&preq, blkif, operation) != 0) {
@@ -537,6 +532,16 @@ static void dispatch_rw_block_io(struct blkif_st *blkif,
                         preq.sector_number + preq.nr_sects, preq.dev);
                 goto fail_response;
         }
+        /* This check _MUST_ be done after vbd_translate as the preq.bdev
+         * is set there. */
+        for (i = 0; i < nseg; i++) {
+                if (((int)preq.sector_number|(int)seg[i].nsec) &
+                    ((bdev_logical_block_size(preq.bdev) >> 9) - 1)) {
+                        DPRINTK("Misaligned I/O request from domain %d",
+                                blkif->domid);
+                        goto fail_response;
+                }
+        }
         /* If we have failed at this point, we need to undo the M2P override,
          * set gnttab_set_unmap_op on all of the grant references and perform
          * the hypercall to unmap the grants - that is all done in