[Qemu-devel] [PATCH v8 12/17] qcow2: Fix refcount blocks beyond image end

[Max Reitz <mreitz@redhat.com>]

If the qcow2 check function detects a refcount block located beyond the
image end, grow the image appropriately. This cannot break anything and
is the logical fix for such a case.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-refcount.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 63 insertions(+), 4 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index c92e1fc..b87eafc 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1575,7 +1575,7 @@ static int check_refblocks(BlockDriverState *bs, BdrvCheckResult *res,
                            int64_t *nb_clusters)
 {
     BDRVQcowState *s = bs->opaque;
-    int64_t i;
+    int64_t i, size;
     int ret;
 
     for(i = 0; i < s->refcount_table_size; i++) {
@@ -1592,9 +1592,68 @@ static int check_refblocks(BlockDriverState *bs, BdrvCheckResult *res,
         }
 
         if (cluster >= *nb_clusters) {
-            fprintf(stderr, "ERROR refcount block %" PRId64
-                    " is outside image\n", i);
-            res->corruptions++;
+            fprintf(stderr, "%s refcount block %" PRId64 " is outside image\n",
+                    fix & BDRV_FIX_ERRORS ? "Repairing" : "ERROR", i);
+
+            if (fix & BDRV_FIX_ERRORS) {
+                int64_t old_nb_clusters = *nb_clusters;
+                uint16_t *new_refcount_table;
+
+                if (offset > INT64_MAX - s->cluster_size) {
+                    ret = -EINVAL;
+                    goto resize_fail;
+                }
+
+                ret = bdrv_truncate(bs->file, offset + s->cluster_size);
+                if (ret < 0) {
+                    goto resize_fail;
+                }
+                size = bdrv_getlength(bs->file);
+                if (size < 0) {
+                    ret = size;
+                    goto resize_fail;
+                }
+
+                *nb_clusters = size_to_clusters(s, size);
+                assert(*nb_clusters >= old_nb_clusters);
+
+                new_refcount_table = g_try_realloc(*refcount_table,
+                                                   *nb_clusters *
+                                                   sizeof(**refcount_table));
+                if (!new_refcount_table) {
+                    *nb_clusters = old_nb_clusters;
+                    res->check_errors++;
+                    return -ENOMEM;
+                }
+                *refcount_table = new_refcount_table;
+
+                memset(*refcount_table + old_nb_clusters, 0,
+                       (*nb_clusters - old_nb_clusters) *
+                       sizeof(**refcount_table));
+
+                if (cluster >= *nb_clusters) {
+                    ret = -EINVAL;
+                    goto resize_fail;
+                }
+
+                res->corruptions_fixed++;
+                ret = inc_refcounts(bs, res, refcount_table, nb_clusters,
+                                    offset, s->cluster_size);
+                if (ret < 0) {
+                    return ret;
+                }
+                /* No need to check whether the refcount is now greater than 1:
+                 * This area was just allocated and zeroed, so it can only be
+                 * exactly 1 after inc_refcounts() */
+                continue;
+
+resize_fail:
+                res->corruptions++;
+                fprintf(stderr, "ERROR could not resize image: %s\n",
+                        strerror(-ret));
+            } else {
+                res->corruptions++;
+            }
             continue;
         }
 
-- 
1.9.3