The commit for 0e4e4318eaa5 increments QCOW2_OL_MAX_BITNR but does not
add an array entry for QCOW2_OL_BITMAP_DIRECTORY_BITNR to metadata_ol_names[].
As a result, an array dereference of metadata_ol_names[8] in
qcow2_pre_write_overlap_check() could result in a read outside of the array bounds.

Fixes: 0e4e4318eaa5 ('qcow2: add overlap check for bitmap directory')

Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Liam Merwick <Liam.Merwick@oracle.com>
---
 block/qcow2-refcount.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 3c539f02e5ec..fb0de187cfd2 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -2719,16 +2719,26 @@ int qcow2_check_metadata_overlap(BlockDriverState *bs, int ign, int64_t offset,
 }
 
 static const char *metadata_ol_names[] = {
-    [QCOW2_OL_MAIN_HEADER_BITNR]    = "qcow2_header",
-    [QCOW2_OL_ACTIVE_L1_BITNR]      = "active L1 table",
-    [QCOW2_OL_ACTIVE_L2_BITNR]      = "active L2 table",
-    [QCOW2_OL_REFCOUNT_TABLE_BITNR] = "refcount table",
-    [QCOW2_OL_REFCOUNT_BLOCK_BITNR] = "refcount block",
-    [QCOW2_OL_SNAPSHOT_TABLE_BITNR] = "snapshot table",
-    [QCOW2_OL_INACTIVE_L1_BITNR]    = "inactive L1 table",
-    [QCOW2_OL_INACTIVE_L2_BITNR]    = "inactive L2 table",
+    [QCOW2_OL_MAIN_HEADER_BITNR]        = "qcow2_header",
+    [QCOW2_OL_ACTIVE_L1_BITNR]          = "active L1 table",
+    [QCOW2_OL_ACTIVE_L2_BITNR]          = "active L2 table",
+    [QCOW2_OL_REFCOUNT_TABLE_BITNR]     = "refcount table",
+    [QCOW2_OL_REFCOUNT_BLOCK_BITNR]     = "refcount block",
+    [QCOW2_OL_SNAPSHOT_TABLE_BITNR]     = "snapshot table",
+    [QCOW2_OL_INACTIVE_L1_BITNR]        = "inactive L1 table",
+    [QCOW2_OL_INACTIVE_L2_BITNR]        = "inactive L2 table",
+    [QCOW2_OL_BITMAP_DIRECTORY_BITNR]   = "bitmap directory",
 };
 
+
+/*
+ * Catch at compile time the case where an overlap detection bit
+ * was added to QCow2MetadataOverlap in block/qcow2.h but a
+ * corresponding entry to metadata_ol_names[] wasn't added.
+ */
+QEMU_BUILD_BUG_ON(QCOW2_OL_MAX_BITNR !=
+    (sizeof(metadata_ol_names) / sizeof(metadata_ol_names[0])));
+
 /*
  * First performs a check for metadata overlaps (through
  * qcow2_check_metadata_overlap); if that fails with a negative value (error
-- 
1.8.3.1

On 08/31/2018 11:36 AM, Liam Merwick wrote:
> The commit for 0e4e4318eaa5 increments QCOW2_OL_MAX_BITNR but does not
> add an array entry for QCOW2_OL_BITMAP_DIRECTORY_BITNR to metadata_ol_names[].
> As a result, an array dereference of metadata_ol_names[8] in
> qcow2_pre_write_overlap_check() could result in a read outside of the array bounds.
> 
> Fixes: 0e4e4318eaa5 ('qcow2: add overlap check for bitmap directory')
> 
> Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Liam Merwick <Liam.Merwick@oracle.com>
> ---
>   block/qcow2-refcount.c | 26 ++++++++++++++++++--------
>   1 file changed, 18 insertions(+), 8 deletions(-)
> 

> +
> +/*
> + * Catch at compile time the case where an overlap detection bit
> + * was added to QCow2MetadataOverlap in block/qcow2.h but a
> + * corresponding entry to metadata_ol_names[] wasn't added.
> + */

I'm not sure the comment adds much value.  I'd be fine with dropping it.

> +QEMU_BUILD_BUG_ON(QCOW2_OL_MAX_BITNR !=
> +    (sizeof(metadata_ol_names) / sizeof(metadata_ol_names[0])));

We have a macro for that.  Spell this:

QEMU_BUILD_BUG_ON(QCOW2_OL_MAX_BITNR != ARRAY_SIZE(metadata_ol_names));

and then you can have

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

On 31/08/18 17:53, Eric Blake wrote:
> On 08/31/2018 11:36 AM, Liam Merwick wrote:
>> The commit for 0e4e4318eaa5 increments QCOW2_OL_MAX_BITNR but does not
>> add an array entry for QCOW2_OL_BITMAP_DIRECTORY_BITNR to 
>> metadata_ol_names[].
>> As a result, an array dereference of metadata_ol_names[8] in
>> qcow2_pre_write_overlap_check() could result in a read outside of the 
>> array bounds.
>>
>> Fixes: 0e4e4318eaa5 ('qcow2: add overlap check for bitmap directory')
>>
>> Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> Signed-off-by: Liam Merwick <Liam.Merwick@oracle.com>
>> ---
>>   block/qcow2-refcount.c | 26 ++++++++++++++++++--------
>>   1 file changed, 18 insertions(+), 8 deletions(-)
>>
> 
>> +
>> +/*
>> + * Catch at compile time the case where an overlap detection bit
>> + * was added to QCow2MetadataOverlap in block/qcow2.h but a
>> + * corresponding entry to metadata_ol_names[] wasn't added.
>> + */
> 
> I'm not sure the comment adds much value.  I'd be fine with dropping it.
> 
>> +QEMU_BUILD_BUG_ON(QCOW2_OL_MAX_BITNR !=
>> +    (sizeof(metadata_ol_names) / sizeof(metadata_ol_names[0])));
> 
> We have a macro for that.  Spell this:
> 
> QEMU_BUILD_BUG_ON(QCOW2_OL_MAX_BITNR != ARRAY_SIZE(metadata_ol_names));
> 
> and then you can have
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 

Thanks, I've updated those and removed the double space in patch6. Will 
be in upcoming v3

Regards,
Liam