[Qemu-devel] [PATCH for-2.0 28/47] qcow2: Check new refcount table size on growth

[Stefan Hajnoczi]

From: Kevin Wolf <address@hidden>

If the size becomes larger than what qcow2_open() would accept, fail the
growing operation.

Signed-off-by: Kevin Wolf <address@hidden>
---
 block/qcow2-refcount.c | 4 ++++
 block/qcow2.c          | 4 +---
 block/qcow2.h          | 9 +++++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 561d659..1c78ff8 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -311,6 +311,10 @@ static int alloc_refcount_block(BlockDriverState *bs,
     uint64_t refcount_block_clusters = 1 << (s->cluster_bits - REFCOUNT_SHIFT);
     uint64_t blocks_used = DIV_ROUND_UP(cluster_index, 
refcount_block_clusters);
 
+    if (blocks_used > QCOW_MAX_REFTABLE_SIZE / sizeof(uint64_t)) {
+        return -EFBIG;
+    }
+
     /* And now we need at least one block more for the new metadata */
     uint64_t table_size = next_refcount_table_size(s, blocks_used + 1);
     uint64_t last_table_size;
diff --git a/block/qcow2.c b/block/qcow2.c
index 464db5c..6c54e2b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -608,9 +608,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, 
int flags,
     s->refcount_table_size =
         header.refcount_table_clusters << (s->cluster_bits - 3);
 
-    if (header.refcount_table_clusters > (0x800000 >> s->cluster_bits)) {
-        /* 8 MB refcount table is enough for 2 PB images at 64k cluster size
-         * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+    if (header.refcount_table_clusters > qcow2_max_refcount_clusters(s)) {
         error_setg(errp, "Reference count table too large");
         ret = -EINVAL;
         goto fail;
diff --git a/block/qcow2.h b/block/qcow2.h
index b153505..4015373 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -40,6 +40,10 @@
 #define QCOW_MAX_CRYPT_CLUSTERS 32
 #define QCOW_MAX_SNAPSHOTS 65536
 
+/* 8 MB refcount table is enough for 2 PB images at 64k cluster size
+ * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+#define QCOW_MAX_REFTABLE_SIZE 0x800000
+
 /* indicate that the refcount of the referenced cluster is exactly one. */
 #define QCOW_OFLAG_COPIED     (1ULL << 63)
 /* indicate that the cluster is compressed (they never have the copied flag) */
@@ -410,6 +414,11 @@ static inline int64_t qcow2_vm_state_offset(BDRVQcowState 
*s)
     return (int64_t)s->l1_vm_state_index << (s->cluster_bits + s->l2_bits);
 }
 
+static inline uint64_t qcow2_max_refcount_clusters(BDRVQcowState *s)
+{
+    return QCOW_MAX_REFTABLE_SIZE >> s->cluster_bits;
+}
+
 static inline int qcow2_get_cluster_type(uint64_t l2_entry)
 {
     if (l2_entry & QCOW_OFLAG_COMPRESSED) {
-- 
1.8.5.3