Fix (at least one cause of) qcow2 corruption. (Nolan Leake)

qcow2's get_cluster_offset() scans forward in the l2 table to find other
clusters that have the same allocation status as the first cluster.
This is used by (among others) qcow_is_allocated().

Unfortunately, it was not checking to be sure that it didn't fall off
the end of the l2 table.  This patch adds that check.

The symptom that motivated me to look into this was that
bdrv_is_allocated() was returning false when there was in fact data
there.  This is one of many ways this bug could lead to data corruption.

I checked the other place that scans for consecutive unallocated blocks
(alloc_cluster_offset()) and it appears to be OK:
    nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);
appears to prevent the same problem from occurring.

Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6977 c046a42c-6fe2-441c-8c8c-71466251a162

diff --git a/block-qcow2.c b/block-qcow2.c
index 60d87a4b8d4db8de0d1e1c4007dae029b2d25927..0e507ca48066fece204481e5d0fbc26ad8dc5fd1 100644 (file)
--- a/block-qcow2.c
+++ b/block-qcow2.c
@@ -761,6 +761,10 @@ static uint64_t get_cluster_offset(BlockDriverState *bs,
 
     nb_available = (nb_available >> 9) + index_in_cluster;
 
+    if (nb_needed > nb_available) {
+        nb_needed = nb_available;
+    }
+
     cluster_offset = 0;
 
     /* seek the the l2 offset in the l1 table */