xen/blkback: don't free be structure too early

BugLink: http://bugs.launchpad.net/bugs/1710646
commit 71df1d7ccad1c36f7321d6b3b48f2ea42681c363 upstream.

The be structure must not be freed when freeing the blkif structure
isn't done. Otherwise a use-after-free of be when unmapping the ring
used for communicating with the frontend will occur in case of a
late call of xenblk_disconnect() (e.g. due to an I/O still active
when trying to disconnect).

Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Steven Haigh <netwiz@crc.id.au>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index f53cff42f8dab8891143ff2d6a3626273857eec6..58f151e283ff9fd781cb1b6a87e9d3f8bc2cb7ab 100644 (file)
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -266,9 +266,10 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 
 static void xen_blkif_free(struct xen_blkif *blkif)
 {
-
-       xen_blkif_disconnect(blkif);
+       WARN_ON(xen_blkif_disconnect(blkif));
        xen_vbd_free(&blkif->vbd);
+       kfree(blkif->be->mode);
+       kfree(blkif->be);
 
        /* Make sure everything is drained before shutting down */
        BUG_ON(blkif->persistent_gnt_c != 0);
@@ -445,8 +446,6 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
                xen_blkif_put(be->blkif);
        }
 
-       kfree(be->mode);
-       kfree(be);
        return 0;
 }