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Blame SOURCES/kvm-backup-Make-sure-that-source-and-target-size-match.patch

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From e56abd782be8bb41bb07c0317d008f95ec9a8ee5 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Wed, 3 Jun 2020 16:03:20 +0100
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Subject: [PATCH 21/26] backup: Make sure that source and target size match
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20200603160325.67506-7-kwolf@redhat.com>
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Patchwork-id: 97107
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O-Subject: [RHEL-AV-8.2.1 qemu-kvm PATCH v2 06/11] backup: Make sure that source and target size match
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Bugzilla: 1778593
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
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Since the introduction of a backup filter node in commit 00e30f05d, the
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backup block job crashes when the target image is smaller than the
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source image because it will try to write after the end of the target
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node without having BLK_PERM_RESIZE. (Previously, the BlockBackend layer
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would have caught this and errored out gracefully.)
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We can fix this and even do better than the old behaviour: Check that
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source and target have the same image size at the start of the block job
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and unshare BLK_PERM_RESIZE. (This permission was already unshared
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before the same commit 00e30f05d, but the BlockBackend that was used to
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make the restriction was removed without a replacement.) This will
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immediately error out when starting the job instead of only when writing
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to a block that doesn't exist in the target.
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Longer target than source would technically work because we would never
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write to blocks that don't exist, but semantically these are invalid,
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too, because a backup is supposed to create a copy, not just an image
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that starts with a copy.
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Fixes: 00e30f05de1d19586345ec373970ef4c192c6270
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1778593
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Cc: qemu-stable@nongnu.org
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Message-Id: <20200430142755.315494-4-kwolf@redhat.com>
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Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 958a04bd32af18d9a207bcc78046e56a202aebc2)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 block/backup-top.c | 14 +++++++++-----
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 block/backup.c     | 14 +++++++++++++-
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 2 files changed, 22 insertions(+), 6 deletions(-)
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diff --git a/block/backup-top.c b/block/backup-top.c
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index b8d863f..6756091 100644
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--- a/block/backup-top.c
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+++ b/block/backup-top.c
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@@ -143,8 +143,10 @@ static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
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          *
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          * Share write to target (child_file), to not interfere
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          * with guest writes to its disk which may be in target backing chain.
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+         * Can't resize during a backup block job because we check the size
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+         * only upfront.
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          */
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-        *nshared = BLK_PERM_ALL;
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+        *nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
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         *nperm = BLK_PERM_WRITE;
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     } else {
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         /* Source child */
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@@ -154,7 +156,7 @@ static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
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         if (perm & BLK_PERM_WRITE) {
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             *nperm = *nperm | BLK_PERM_CONSISTENT_READ;
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         }
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-        *nshared &= ~BLK_PERM_WRITE;
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+        *nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
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     }
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 }
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@@ -187,10 +189,12 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
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 {
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     Error *local_err = NULL;
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     BDRVBackupTopState *state;
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-    BlockDriverState *top = bdrv_new_open_driver(&bdrv_backup_top_filter,
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-                                                 filter_node_name,
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-                                                 BDRV_O_RDWR, errp);
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+    BlockDriverState *top;
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+
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+    assert(source->total_sectors == target->total_sectors);
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+    top = bdrv_new_open_driver(&bdrv_backup_top_filter, filter_node_name,
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+                               BDRV_O_RDWR, errp);
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     if (!top) {
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         return NULL;
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     }
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diff --git a/block/backup.c b/block/backup.c
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index 7c6ddd2..821c9fb 100644
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--- a/block/backup.c
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+++ b/block/backup.c
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@@ -348,7 +348,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
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                   BlockCompletionFunc *cb, void *opaque,
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                   JobTxn *txn, Error **errp)
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 {
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-    int64_t len;
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+    int64_t len, target_len;
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     BackupBlockJob *job = NULL;
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     int64_t cluster_size;
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     BdrvRequestFlags write_flags;
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@@ -413,6 +413,18 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
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         goto error;
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     }
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+    target_len = bdrv_getlength(target);
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+    if (target_len < 0) {
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+        error_setg_errno(errp, -target_len, "Unable to get length for '%s'",
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+                         bdrv_get_device_or_node_name(bs));
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+        goto error;
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+    }
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+
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+    if (target_len != len) {
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+        error_setg(errp, "Source and target image have different sizes");
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+        goto error;
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+    }
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+
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     cluster_size = backup_calculate_cluster_size(target, errp);
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     if (cluster_size < 0) {
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         goto error;
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-- 
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1.8.3.1
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