xen/blkback: Check device permissions before allowing OP_DISCARD

commit 604c499cbbcc3d5fe5fb8d53306aa0fae1990109 upstream.

We need to make sure that the device is not RO or that
the request is not past the number of sectors we want to
issue the DISCARD operation for.

This fixes CVE-2013-2140.

Acked-by: Jan Beulich <JBeulich@suse.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
[v1: Made it pr_warn instead of pr_debug]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index dd5b2fed97e9..d81dfca755d1 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -647,7 +647,18 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
         int status = BLKIF_RSP_OKAY;
         struct block_device *bdev = blkif->vbd.bdev;
         unsigned long secure;
+        struct phys_req preq;
+
+        preq.sector_number = req->u.discard.sector_number;
+        preq.nr_sects      = req->u.discard.nr_sectors;
 
+        err = xen_vbd_translate(&preq, blkif, WRITE);
+        if (err) {
+                pr_warn(DRV_PFX "access denied: DISCARD [%llu->%llu] on dev=%04x\n",
+                        preq.sector_number,
+                        preq.sector_number + preq.nr_sects, blkif->vbd.pdevice);
+                goto fail_response;
+        }
         blkif->st_ds_req++;
 
         xen_blkif_get(blkif);
@@ -658,7 +669,7 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
         err = blkdev_issue_discard(bdev, req->u.discard.sector_number,
                                    req->u.discard.nr_sectors,
                                    GFP_KERNEL, secure);
-
+fail_response:
         if (err == -EOPNOTSUPP) {
                 pr_debug(DRV_PFX "discard op failed, not supported\n");
                 status = BLKIF_RSP_EOPNOTSUPP;