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[PULL,01/17] qcow2: Fix alloc_clusters_noref() overflow detection

Message ID 1399662217-31148-2-git-send-email-stefanha@redhat.com
State New
Headers show

Commit Message

Stefan Hajnoczi May 9, 2014, 7:03 p.m. UTC 
From: Max Reitz <mreitz@redhat.com>

If the very first allocation has a length of 0, the free_cluster_index
is still 0 after the for loop, which means that subtracting one from it
will underflow and signal an invalid range of clusters by returning
-EFBIG. However, there is no such range, as its length is 0.

Fix this by preventing underflows on free_cluster_index during the
check.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/qcow2-refcount.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
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Patch

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index e79895d..9507aef 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -656,7 +656,9 @@  retry:
 
     /* Make sure that all offsets in the "allocated" range are representable
      * in an int64_t */
-    if (s->free_cluster_index - 1 > (INT64_MAX >> s->cluster_bits)) {
+    if (s->free_cluster_index > 0 &&
+        s->free_cluster_index - 1 > (INT64_MAX >> s->cluster_bits))
+    {
         return -EFBIG;
     }