From e56abd782be8bb41bb07c0317d008f95ec9a8ee5 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Wed, 3 Jun 2020 16:03:20 +0100
Subject: [PATCH 21/26] backup: Make sure that source and target size match

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20200603160325.67506-7-kwolf@redhat.com>
Patchwork-id: 97107
O-Subject: [RHEL-AV-8.2.1 qemu-kvm PATCH v2 06/11] backup: Make sure that source and target size match
Bugzilla: 1778593
RH-Acked-by: Eric Blake <eblake@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>

Since the introduction of a backup filter node in commit 00e30f05d, the
backup block job crashes when the target image is smaller than the
source image because it will try to write after the end of the target
node without having BLK_PERM_RESIZE. (Previously, the BlockBackend layer
would have caught this and errored out gracefully.)

We can fix this and even do better than the old behaviour: Check that
source and target have the same image size at the start of the block job
and unshare BLK_PERM_RESIZE. (This permission was already unshared
before the same commit 00e30f05d, but the BlockBackend that was used to
make the restriction was removed without a replacement.) This will
immediately error out when starting the job instead of only when writing
to a block that doesn't exist in the target.

Longer target than source would technically work because we would never
write to blocks that don't exist, but semantically these are invalid,
too, because a backup is supposed to create a copy, not just an image
that starts with a copy.

Fixes: 00e30f05de1d19586345ec373970ef4c192c6270
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1778593
Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200430142755.315494-4-kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 958a04bd32af18d9a207bcc78046e56a202aebc2)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 block/backup-top.c | 14 +++++++++-----
 block/backup.c     | 14 +++++++++++++-
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/block/backup-top.c b/block/backup-top.c
index b8d863f..6756091 100644
--- a/block/backup-top.c
+++ b/block/backup-top.c
@@ -143,8 +143,10 @@ static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
          *
          * Share write to target (child_file), to not interfere
          * with guest writes to its disk which may be in target backing chain.
+         * Can't resize during a backup block job because we check the size
+         * only upfront.
          */
-        *nshared = BLK_PERM_ALL;
+        *nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
         *nperm = BLK_PERM_WRITE;
     } else {
         /* Source child */
@@ -154,7 +156,7 @@ static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
         if (perm & BLK_PERM_WRITE) {
             *nperm = *nperm | BLK_PERM_CONSISTENT_READ;
         }
-        *nshared &= ~BLK_PERM_WRITE;
+        *nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
     }
 }
 
@@ -187,10 +189,12 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
 {
     Error *local_err = NULL;
     BDRVBackupTopState *state;
-    BlockDriverState *top = bdrv_new_open_driver(&bdrv_backup_top_filter,
-                                                 filter_node_name,
-                                                 BDRV_O_RDWR, errp);
+    BlockDriverState *top;
+
+    assert(source->total_sectors == target->total_sectors);
 
+    top = bdrv_new_open_driver(&bdrv_backup_top_filter, filter_node_name,
+                               BDRV_O_RDWR, errp);
     if (!top) {
         return NULL;
     }
diff --git a/block/backup.c b/block/backup.c
index 7c6ddd2..821c9fb 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -348,7 +348,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
                   BlockCompletionFunc *cb, void *opaque,
                   JobTxn *txn, Error **errp)
 {
-    int64_t len;
+    int64_t len, target_len;
     BackupBlockJob *job = NULL;
     int64_t cluster_size;
     BdrvRequestFlags write_flags;
@@ -413,6 +413,18 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         goto error;
     }
 
+    target_len = bdrv_getlength(target);
+    if (target_len < 0) {
+        error_setg_errno(errp, -target_len, "Unable to get length for '%s'",
+                         bdrv_get_device_or_node_name(bs));
+        goto error;
+    }
+
+    if (target_len != len) {
+        error_setg(errp, "Source and target image have different sizes");
+        goto error;
+    }
+
     cluster_size = backup_calculate_cluster_size(target, errp);
     if (cluster_size < 0) {
         goto error;
-- 
1.8.3.1

