[Qemu-devel] [PATCH v4 05/10] 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 | 62 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 58 insertions(+), 4 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index babe6cb..394a402 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1505,7 +1505,8 @@ 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++) {
         uint64_t offset, cluster;
@@ -1521,9 +1522,62 @@ 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;
+
+                if (offset + s->cluster_size < offset ||
+                    offset + s->cluster_size > INT64_MAX)
+                {
+                    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);
+
+                *refcount_table = g_try_realloc(*refcount_table,
+                        *nb_clusters * sizeof(uint16_t));
+                if (!*refcount_table) {
+                    res->check_errors++;
+                    return -ENOMEM;
+                }
+
+                memset(*refcount_table + old_nb_clusters, 0,
+                       (*nb_clusters - old_nb_clusters) * sizeof(uint16_t));
+
+                if (cluster >= *nb_clusters) {
+                    ret = -EINVAL;
+                    goto resize_fail;
+                }
+
+                res->corruptions_fixed++;
+                inc_refcounts(bs, res, *refcount_table, *nb_clusters,
+                              offset, s->cluster_size);
+                /* 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;
         }
 
-- 
2.1.0