[PATCH v3 2/4] bitmap: Enforce maximum bitmap name length

[Eric Blake <eblake@redhat.com>]

We document that for qcow2 persistent bitmaps, the name cannot exceed
1023 bytes.  It is inconsistent if transient bitmaps do not have to
abide by the same limit, and it is unlikely that any existing client
even cares about using bitmap names this long.  It's time to codify
that ALL bitmaps managed by qemu (whether persistent in qcow2 or not)
have a documented maximum length.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 qapi/block-core.json         |  2 +-
 include/block/dirty-bitmap.h |  2 ++
 block/dirty-bitmap.c         | 12 +++++++++---
 block/qcow2-bitmap.c         |  2 ++
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index aa97ee264112..0cf68fea1450 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2042,7 +2042,7 @@
 #
 # @node: name of device/node which the bitmap is tracking
 #
-# @name: name of the dirty bitmap
+# @name: name of the dirty bitmap (must be less than 1024 bytes)
 #
 # @granularity: the bitmap granularity, default is 64k for
 #               block-dirty-bitmap-add
diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
index 958e7474fb51..e2b20ecab9a3 100644
--- a/include/block/dirty-bitmap.h
+++ b/include/block/dirty-bitmap.h
@@ -14,6 +14,8 @@ typedef enum BitmapCheckFlags {
                              BDRV_BITMAP_INCONSISTENT)
 #define BDRV_BITMAP_ALLOW_RO (BDRV_BITMAP_BUSY | BDRV_BITMAP_INCONSISTENT)

+#define BDRV_BITMAP_MAX_NAME_SIZE 1023
+
 BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
                                           uint32_t granularity,
                                           const char *name,
diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 4bbb251b2c9c..7039e8252009 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -104,9 +104,15 @@ BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,

     assert(is_power_of_2(granularity) && granularity >= BDRV_SECTOR_SIZE);

-    if (name && bdrv_find_dirty_bitmap(bs, name)) {
-        error_setg(errp, "Bitmap already exists: %s", name);
-        return NULL;
+    if (name) {
+        if (bdrv_find_dirty_bitmap(bs, name)) {
+            error_setg(errp, "Bitmap already exists: %s", name);
+            return NULL;
+        }
+        if (strlen(name) > BDRV_BITMAP_MAX_NAME_SIZE) {
+            error_setg(errp, "Bitmap name too long: %s", name);
+            return NULL;
+        }
     }
     bitmap_size = bdrv_getlength(bs);
     if (bitmap_size < 0) {
diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index ef9ef628a0d0..809bbc5d20c8 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -42,6 +42,8 @@
 #define BME_MIN_GRANULARITY_BITS 9
 #define BME_MAX_NAME_SIZE 1023

+QEMU_BUILD_BUG_ON(BME_MAX_NAME_SIZE != BDRV_BITMAP_MAX_NAME_SIZE);
+
 #if BME_MAX_TABLE_SIZE * 8ULL > INT_MAX
 #error In the code bitmap table physical size assumed to fit into int
 #endif
-- 
2.21.0