xen/blkback: Check device permissions before allowing OP_DISCARD

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.

Cc: stable@vger.kernel.org
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>

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index e79ab45592332082662d3693b91cfd6def90493d..4119bcdefd1affc8a8ea2dd928a45dd128b36828 100644 (file)
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -876,7 +876,18 @@ 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);
@@ -887,7 +898,7 @@ 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;