[43/55] qcow2: Limit total allocation range to INT_MAX

Commit Message

Michael Roth Nov. 5, 2019, 8:52 p.m. UTC

From: Max Reitz <[e-mail]>

When the COW areas are included, the size of an allocation can exceed
INT_MAX.  This is kind of limited by handle_alloc() in that it already
caps avail_bytes at INT_MAX, but the number of clusters still reflects
the original length.

This can have all sorts of effects, ranging from the storage layer write
call failing to image corruption.  (If there were no image corruption,
then I suppose there would be data loss because the .cow_end area is
forced to be empty, even though there might be something we need to
COW.)

Fix all of it by limiting nb_clusters so the equivalent number of bytes
will not exceed INT_MAX.

Cc: [e-mail]
Signed-off-by: Max Reitz <[e-mail]>
Reviewed-by: Eric Blake <[e-mail]>
Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>
Signed-off-by: Kevin Wolf <[e-mail]>
(cherry picked from commit d1b9d19f99586b33795e20a79f645186ccbc070f)
Signed-off-by: Michael Roth <[e-mail]>
---
 block/qcow2-cluster.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Patch

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 760564c8fb..f8576031b6 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1341,6 +1341,9 @@  static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
     nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
     assert(nb_clusters <= INT_MAX);
 
+    /* Limit total allocation byte count to INT_MAX */
+    nb_clusters = MIN(nb_clusters, INT_MAX >> s->cluster_bits);
+
     /* Find L2 entry for the first involved cluster */
     ret = get_cluster_table(bs, guest_offset, &l2_slice, &l2_index);
     if (ret < 0) {
@@ -1429,7 +1432,7 @@  static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
      * request actually writes to (excluding COW at the end)
      */
     uint64_t requested_bytes = *bytes + offset_into_cluster(s, guest_offset);
-    int avail_bytes = MIN(INT_MAX, nb_clusters << s->cluster_bits);
+    int avail_bytes = nb_clusters << s->cluster_bits;
     int nb_bytes = MIN(requested_bytes, avail_bytes);
     QCowL2Meta *old_m = *m;