qcow2: Refuse to get unaligned offsets from cache

Instead of using an assertion, it is better to emit a corruption event
here.  Checking all offsets for correct alignment can be tedious and it
is easily possible to forget to do so.  qcow2_cache_do_get() is a
function every L2 and refblock access has to go through, so this is a
good central point to add such a check.

And for good measure, let us also add an assertion that the offset is
non-zero.  Making this a corruption event is not feasible, because a
zero offset usually means something special (such as the cluster is
unused), so all callers should be checking this anyway.  If they do not,
it is their fault, hence the assertion here.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20171110203111.7666-6-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/qemu-iotests/060 b/tests/qemu-iotests/060
index c230696b3a..1eca09417b 100755
--- a/tests/qemu-iotests/060
+++ b/tests/qemu-iotests/060
@@ -405,6 +405,27 @@ _check_test_img -r all
 $QEMU_IMG resize --shrink "$TEST_IMG" 32M
 _img_info | grep 'virtual size'
 
+echo
+echo "=== Discarding a refblock covered by an unaligned refblock ==="
+echo
+
+IMGOPTS='refcount_bits=1' _make_test_img 64M
+
+# Same as above
+poke_file "$TEST_IMG" "$(($rt_offset+8))" "\x00\x00\x00\x10\x00\x00\x00\x00"
+# But now we actually "create" an unaligned third refblock
+poke_file "$TEST_IMG" "$(($rt_offset+16))" "\x00\x00\x00\x00\x00\x00\x02\x00"
+$QEMU_IMG resize --shrink "$TEST_IMG" 32M
+
+echo '--- Repairing ---'
+# Fails the first repair because the corruption prevents the check
+# function from double-checking
+# (Using -q for the first invocation, because otherwise the
+#  double-check error message appears above the summary for some
+#  reason -- so let's just hide the summary)
+_check_test_img -q -r all
+_check_test_img -r all
+
 # success, all done
 echo "*** done"
 rm -f $seq.full