Blame SOURCES/kvm-qcow2-Catch-host_offset-for-data-allocation.patch

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From cd10207e755b1b0470503c72c78a8d927f87a37a Mon Sep 17 00:00:00 2001
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From: Max Reitz <mreitz@redhat.com>
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Date: Sat, 13 Jun 2015 16:21:58 +0200
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Subject: [PATCH 04/42] qcow2: Catch !*host_offset for data allocation
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Message-id: <1434212556-3927-5-git-send-email-mreitz@redhat.com>
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Patchwork-id: 66023
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O-Subject: [RHEL-7.2 qemu-kvm PATCH 04/42] qcow2: Catch !*host_offset for data allocation
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Bugzilla: 1129893
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RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
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RH-Acked-by: Fam Zheng <famz@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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BZ: 1129893
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qcow2_alloc_cluster_offset() uses host_offset == 0 as "no preferred
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offset" for the (data) cluster range to be allocated. However, this
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offset is actually valid and may be allocated on images with a corrupted
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refcount table or first refcount block.
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In this case, the corruption prevention should normally catch that
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write anyway (because it would overwrite the image header). But since 0
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is a special value here, the function assumes that nothing has been
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allocated at all which it asserts against.
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Because this condition is not qemu's fault but rather that of a broken
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image, it shouldn't throw an assertion but rather mark the image corrupt
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and show an appropriate message, which this patch does by calling the
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corruption check earlier than it would be called normally (before the
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assertion).
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Signed-off-by: Max Reitz <mreitz@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit ff52aab2df5c5e10f231481961b88d25a3021724)
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Signed-off-by: Max Reitz <mreitz@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 block/qcow2-cluster.c | 11 +++++++++++
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 1 file changed, 11 insertions(+)
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diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
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index 1b9609f..f2f1170 100644
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--- a/block/qcow2-cluster.c
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+++ b/block/qcow2-cluster.c
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@@ -1089,6 +1089,17 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
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         return 0;
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     }
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+    /* !*host_offset would overwrite the image header and is reserved for "no
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+     * host offset preferred". If 0 was a valid host offset, it'd trigger the
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+     * following overlap check; do that now to avoid having an invalid value in
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+     * *host_offset. */
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+    if (!alloc_cluster_offset) {
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+        ret = qcow2_pre_write_overlap_check(bs, 0, alloc_cluster_offset,
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+                                            nb_clusters * s->cluster_size);
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+        assert(ret < 0);
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+        goto fail;
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+    }
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+
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     /*
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      * Save info needed for meta data update.
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      *
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-- 
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1.8.3.1
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