[PATCH v6 09/12] qcow2: introduce host-range-refs

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

We have a bug in qcow2: assume we've started data write into host
cluster A. s->lock is unlocked. During the write the refcount of
cluster A may become zero, cluster may be reallocated for other needs,
and our in-flight write become a use-after-free. More details will be
in the further commit which actually fixes the bug.

For now, let's prepare infrastructure for the following fix. We are
going to track these in-flight data writes and other operations. So, we
create a hash map

  cluster_index -> HostCluster

And for each HostCluster we calculate number of in-flight operations on
it (which does qcow2_host_range_ref() of course).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/qcow2.h                 |  12 ++++
 block/qcow2-host-range-refs.c | 127 ++++++++++++++++++++++++++++++++++
 block/qcow2.c                 |   3 +
 block/meson.build             |   1 +
 4 files changed, 143 insertions(+)
 create mode 100644 block/qcow2-host-range-refs.c

diff --git a/block/qcow2.h b/block/qcow2.h
index 511db948ec..d6de9543c4 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -420,6 +420,9 @@ typedef struct BDRVQcow2State {
      * is to convert the image with the desired compression type set.
      */
     Qcow2CompressionType compression_type;
+
+    /* For qcow2-host-range-refs.c */
+    GHashTable *host_range_refs;
 } BDRVQcow2State;
 
 typedef struct Qcow2COWRegion {
@@ -899,6 +902,15 @@ int qcow2_detect_metadata_preallocation(BlockDriverState *bs);
 void qcow2_cache_host_discard(BlockDriverState *bs,
                               uint64_t offset, uint64_t length);
 
+void qcow2_init_host_range_refs(BDRVQcow2State *s);
+void qcow2_release_host_range_refs(BDRVQcow2State *s);
+void qcow2_host_range_ref(BlockDriverState *bs, int64_t offset,
+                               int64_t length);
+void qcow2_host_range_unref(BlockDriverState *bs, int64_t offset,
+                               int64_t length);
+uint64_t qcow2_get_host_range_refcnt(BlockDriverState *bs,
+                                     int64_t cluster_index);
+
 /* qcow2-cluster.c functions */
 int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
                         bool exact_size);
diff --git a/block/qcow2-host-range-refs.c b/block/qcow2-host-range-refs.c
new file mode 100644
index 0000000000..54f0be27a4
--- /dev/null
+++ b/block/qcow2-host-range-refs.c
@@ -0,0 +1,127 @@
+/*
+ * Block driver for the QCOW version 2 format
+ *
+ * Copyright (c) 2021 Virtuozzo International GmbH.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu/osdep.h"
+#include "qcow2.h"
+
+typedef struct HostCluster {
+    uint64_t host_range_refcnt;
+
+    /* For convenience, keep cluster_index here */
+    int64_t cluster_index;
+} HostCluster;
+
+void qcow2_init_host_range_refs(BDRVQcow2State *s)
+{
+    s->host_range_refs =
+        g_hash_table_new_full(g_int64_hash, g_int64_equal, g_free, g_free);
+}
+
+void qcow2_release_host_range_refs(BDRVQcow2State *s)
+{
+    assert(g_hash_table_size(s->host_range_refs) == 0);
+    g_hash_table_unref(s->host_range_refs);
+}
+
+static HostCluster *find_host_cluster(BDRVQcow2State *s, int64_t cluster_index)
+{
+    HostCluster *cl;
+
+    if (!s->host_range_refs) {
+        return NULL;
+    }
+
+    cl = g_hash_table_lookup(s->host_range_refs, &cluster_index);
+
+    if (cl) {
+        assert(cl->host_range_refcnt > 0);
+    }
+
+    return cl;
+}
+
+uint64_t qcow2_get_host_range_refcnt(BlockDriverState *bs,
+                                     int64_t cluster_index)
+{
+    BDRVQcow2State *s = bs->opaque;
+    HostCluster *cl = find_host_cluster(s, cluster_index);
+
+    if (!cl) {
+        return 0;
+    }
+
+    return cl->host_range_refcnt;
+}
+
+/* Inrease host_range_refcnt of clusters intersecting with range */
+void coroutine_fn
+qcow2_host_range_ref(BlockDriverState *bs, int64_t offset, int64_t length)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int64_t start, last, cluster_index;
+
+    start = start_of_cluster(s, offset) >> s->cluster_bits;
+    last = start_of_cluster(s, offset + length - 1) >> s->cluster_bits;
+    for (cluster_index = start; cluster_index <= last; cluster_index++) {
+        HostCluster *cl = find_host_cluster(s, cluster_index);
+
+        if (!cl) {
+            cl = g_new(HostCluster, 1);
+            *cl = (HostCluster) {
+                .cluster_index = cluster_index,
+                .host_range_refcnt = 1,
+            };
+            g_hash_table_insert(s->host_range_refs,
+                                g_memdup(&cluster_index,
+                                         sizeof(cluster_index)), cl);
+        } else {
+            cl->host_range_refcnt++;
+        }
+        continue;
+    }
+}
+
+/* Decrease host_range_refcnt of clusters intersecting with range */
+void coroutine_fn
+qcow2_host_range_unref(BlockDriverState *bs, int64_t offset, int64_t length)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int64_t start, last, cluster_index;
+
+    start = start_of_cluster(s, offset) >> s->cluster_bits;
+    last = start_of_cluster(s, offset + length - 1) >> s->cluster_bits;
+    for (cluster_index = start; cluster_index <= last; cluster_index++) {
+        HostCluster *cl = find_host_cluster(s, cluster_index);
+
+        assert(cl);
+        assert(cl->host_range_refcnt >= 1);
+
+        if (cl->host_range_refcnt > 1) {
+            cl->host_range_refcnt--;
+            continue;
+        }
+
+        g_hash_table_remove(s->host_range_refs, &cluster_index);
+    }
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index be62585e03..aa298c9e42 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1834,6 +1834,7 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
 #endif
 
     qemu_co_queue_init(&s->thread_task_queue);
+    qcow2_init_host_range_refs(s);
 
     return ret;
 
@@ -2714,6 +2715,8 @@ static void qcow2_close(BlockDriverState *bs)
     g_free(s->image_backing_file);
     g_free(s->image_backing_format);
 
+    qcow2_release_host_range_refs(s);
+
     if (has_data_file(bs)) {
         bdrv_unref_child(bs, s->data_file);
         s->data_file = NULL;
diff --git a/block/meson.build b/block/meson.build
index d21990ec95..a9bf6fde0c 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -25,6 +25,7 @@ block_ss.add(files(
   'qcow2-bitmap.c',
   'qcow2-cache.c',
   'qcow2-cluster.c',
+  'qcow2-host-range-refs.c',
   'qcow2-refcount.c',
   'qcow2-snapshot.c',
   'qcow2-threads.c',
-- 
2.29.2