[qemu-xen stable-4.13] block/qcow2: Fix corruption introduced by commit 8ac0f15f335

[patchbot@xxxxxxx]

commit 84f22c728520792f1010074e0d5ac2ec8e2e372c
Author:     Maxim Levitsky <mlevitsk@xxxxxxxxxx>
AuthorDate: Sun Sep 15 23:36:53 2019 +0300
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed Oct 30 11:34:26 2019 -0500

    block/qcow2: Fix corruption introduced by commit 8ac0f15f335
    
    This fixes subtle corruption introduced by luks threaded encryption
    in commit 8ac0f15f335
    
    Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1745922
    
    The corruption happens when we do a write that
       * writes to two or more unallocated clusters at once
       * doesn't fully cover the first sector
       * doesn't fully cover the last sector
       * uses luks encryption
    
    In this case, when allocating the new clusters we COW both areas
    prior to the write and after the write, and we encrypt them.
    
    The above mentioned commit accidentally made it so we encrypt the
    second COW area using the physical cluster offset of the first area.
    
    The problem is that offset_in_cluster in do_perform_cow_encrypt
    can be larger that the cluster size, thus cluster_offset
    will no longer point to the start of the cluster at which encrypted
    area starts.
    
    Next patch in this series will refactor the code to avoid all these
    assumptions.
    
    In the bugreport that was triggered by rebasing a luks image to new,
    zero filled base, which lot of such writes, and causes some files
    with zero areas to contain garbage there instead.
    But as described above it can happen elsewhere as well
    
    Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
    Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    Message-id: 20190915203655.21638-2-mlevitsk@xxxxxxxxxx
    Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx>
    Signed-off-by: Max Reitz <mreitz@xxxxxxxxxx>
    (cherry picked from commit 38e7d54bdc518b5a05a922467304bcace2396945)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 block/qcow2-cluster.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index cc5609e27a..760564c8fb 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -473,9 +473,10 @@ static bool coroutine_fn 
do_perform_cow_encrypt(BlockDriverState *bs,
         assert((offset_in_cluster & ~BDRV_SECTOR_MASK) == 0);
         assert((bytes & ~BDRV_SECTOR_MASK) == 0);
         assert(s->crypto);
-        if (qcow2_co_encrypt(bs, cluster_offset,
-                             src_cluster_offset + offset_in_cluster,
-                             buffer, bytes) < 0) {
+        if (qcow2_co_encrypt(bs,
+                start_of_cluster(s, cluster_offset + offset_in_cluster),
+                src_cluster_offset + offset_in_cluster,
+                buffer, bytes) < 0) {
             return false;
         }
     }
--
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