[PATCH 3.10 060/173] xen/blkback: fix reference counting

Greg Kroah-Hartman
2013-12-02T19:10:43Z

From: Vegard Nossum <vegard.nossum@oracle.com>

commit ea5ec76d76da9279d12027c1828544c5ccbe7932 upstream.

If the permission check fails, we drop a reference to the blkif without
having taken it in the first place. The bug was introduced in commit
604c499cbbcc3d5fe5fb8d53306aa0fae1990109 (xen/blkback: Check device
permissions before allowing OP_DISCARD).

Cc: Jan Beulich <JBeulich@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/xen-blkback/blkback.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -649,6 +649,8 @@ static int dispatch_discard_io(struct xe
unsigned long secure;
struct phys_req preq;

+ xen_blkif_get(blkif);
+
preq.sector_number = req->u.discard.sector_number;
preq.nr_sects = req->u.discard.nr_sectors;

@@ -661,7 +663,6 @@ static int dispatch_discard_io(struct xe
}
blkif->st_ds_req++;

- xen_blkif_get(blkif);
secure = (blkif->vbd.discard_secure &&
(req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
BLKDEV_DISCARD_SECURE : 0;