From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 28 May 2010 10:21:27 +0000 (+0200)
Subject: qcow2: Fix corruption after error in update_refcount
X-Git-Tag: v0.12.5~25
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a513171f809da4e83800e6bd6e7518dd4b190d9f;p=thirdparty%2Fqemu.git

qcow2: Fix corruption after error in update_refcount

After it is done with updating refcounts in the cache, update_refcount writes
all changed entries to disk. If a refcount block allocation fails, however,
there was no change yet and therefore first_index = last_index = -1. Don't
treat -1 as a normal sector index (resulting in a 512 byte write!) but return
without updating anything in this case.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 86fa8da83771238de55dc44819a1a27bafef5353)
---

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index fa78e46ee22..465d5d36e8f 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -402,6 +402,10 @@ static int write_refcount_block_entries(BDRVQcowState *s,
         return 0;
     }
 
+    if (first_index < 0) {
+        return 0;
+    }
+
     first_index &= ~(REFCOUNTS_PER_SECTOR - 1);
     last_index = (last_index + REFCOUNTS_PER_SECTOR)
         & ~(REFCOUNTS_PER_SECTOR - 1);