qcow2: Metadata overlap checks

Two new functions are added; the first one checks a given range in the
image file for overlaps with metadata (main header, L1 tables, L2
tables, refcount table and blocks).

The second one should be used immediately before writing to the image
file as it calls the first function and, upon collision, marks the
image as corrupt and makes the BDS unusable, thereby preventing
further access.

Both functions take a bitmask argument specifying the structures which
should be checked for overlaps, making it possible to also check
metadata writes against colliding with other structures.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/block/qcow2.h b/block/qcow2.h
index 32ecb338ab..d4448c6350 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -289,6 +289,40 @@ enum {
     QCOW2_CLUSTER_ZERO
 };
 
+typedef enum QCow2MetadataOverlap {
+    QCOW2_OL_MAIN_HEADER_BITNR    = 0,
+    QCOW2_OL_ACTIVE_L1_BITNR      = 1,
+    QCOW2_OL_ACTIVE_L2_BITNR      = 2,
+    QCOW2_OL_REFCOUNT_TABLE_BITNR = 3,
+    QCOW2_OL_REFCOUNT_BLOCK_BITNR = 4,
+    QCOW2_OL_SNAPSHOT_TABLE_BITNR = 5,
+    QCOW2_OL_INACTIVE_L1_BITNR    = 6,
+    QCOW2_OL_INACTIVE_L2_BITNR    = 7,
+
+    QCOW2_OL_MAX_BITNR            = 8,
+
+    QCOW2_OL_NONE           = 0,
+    QCOW2_OL_MAIN_HEADER    = (1 << QCOW2_OL_MAIN_HEADER_BITNR),
+    QCOW2_OL_ACTIVE_L1      = (1 << QCOW2_OL_ACTIVE_L1_BITNR),
+    QCOW2_OL_ACTIVE_L2      = (1 << QCOW2_OL_ACTIVE_L2_BITNR),
+    QCOW2_OL_REFCOUNT_TABLE = (1 << QCOW2_OL_REFCOUNT_TABLE_BITNR),
+    QCOW2_OL_REFCOUNT_BLOCK = (1 << QCOW2_OL_REFCOUNT_BLOCK_BITNR),
+    QCOW2_OL_SNAPSHOT_TABLE = (1 << QCOW2_OL_SNAPSHOT_TABLE_BITNR),
+    QCOW2_OL_INACTIVE_L1    = (1 << QCOW2_OL_INACTIVE_L1_BITNR),
+    /* NOTE: Checking overlaps with inactive L2 tables will result in bdrv
+     * reads. */
+    QCOW2_OL_INACTIVE_L2    = (1 << QCOW2_OL_INACTIVE_L2_BITNR),
+} QCow2MetadataOverlap;
+
+/* Perform all overlap checks which don't require disk access */
+#define QCOW2_OL_CACHED \
+    (QCOW2_OL_MAIN_HEADER | QCOW2_OL_ACTIVE_L1 | QCOW2_OL_ACTIVE_L2 | \
+     QCOW2_OL_REFCOUNT_TABLE | QCOW2_OL_REFCOUNT_BLOCK | \
+     QCOW2_OL_SNAPSHOT_TABLE | QCOW2_OL_INACTIVE_L1)
+
+/* The default checks to perform */
+#define QCOW2_OL_DEFAULT QCOW2_OL_CACHED
+
 #define L1E_OFFSET_MASK 0x00ffffffffffff00ULL
 #define L2E_OFFSET_MASK 0x00ffffffffffff00ULL
 #define L2E_COMPRESSED_OFFSET_SIZE_MASK 0x3fffffffffffffffULL
@@ -390,6 +424,11 @@ int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res,
 
 void qcow2_process_discards(BlockDriverState *bs, int ret);
 
+int qcow2_check_metadata_overlap(BlockDriverState *bs, int chk, int64_t offset,
+                                 int64_t size);
+int qcow2_pre_write_overlap_check(BlockDriverState *bs, int chk, int64_t offset,
+                                  int64_t size);
+
 /* qcow2-cluster.c functions */
 int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
                         bool exact_size);