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>

diff --git a/drivers/xen/blkback/blkback.c b/drivers/xen/blkback/blkback.c
index c645c83..a0d3227 100644 (file)
--- 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