[Xen-devel] [PATCH 2/3] xen/blkback: don't free be structure too early

[Juergen Gross <jgross@xxxxxxxx>]

The be structure must nor 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).

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Glenn Enright <glenn@xxxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/block/xen-blkback/xenbus.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c 
b/drivers/block/xen-blkback/xenbus.c
index e68df9de8858..4d2f57fa35da 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -315,9 +315,10 @@ 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 */
        kmem_cache_free(xen_blkif_cachep, blkif);
@@ -514,8 +515,6 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
                xen_blkif_put(be->blkif);
        }
 
-       kfree(be->mode);
-       kfree(be);
        return 0;
 }
 
-- 
2.12.0


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