[Qemu-devel] [PATCH v2 2/7] block/qcow2-refcount: avoid eating RAM

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

qcow2_inc_refcounts_imrt() (through realloc_refcount_array()) can eat
an unpredictable amount of memory on corrupted table entries, which are
referencing regions far beyond the end of file.

Prevent this, by skipping such regions from further processing.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/qcow2-refcount.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 615847eb09..566c19fbfa 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1499,12 +1499,26 @@ int qcow2_inc_refcounts_imrt(BlockDriverState *bs, BdrvCheckResult *res,
 {
     BDRVQcow2State *s = bs->opaque;
     uint64_t start, last, cluster_offset, k, refcount;
+    int64_t file_len;
     int ret;
 
     if (size <= 0) {
         return 0;
     }
 
+    file_len = bdrv_getlength(bs->file->bs);
+    if (file_len < 0) {
+        return file_len;
+    }
+
+    if (offset + size - file_len > s->cluster_size) {
+        fprintf(stderr, "ERROR: counting reference for region exceeding the "
+                "end of the file by more than one cluster: offset 0x%" PRIx64
+                " size 0x%" PRIx64 "\n", offset, size);
+        res->corruptions++;
+        return 0;
+    }
+
     start = start_of_cluster(s, offset);
     last = start_of_cluster(s, offset + size - 1);
     for(cluster_offset = start; cluster_offset <= last;
-- 
2.11.1