azure: case-insensitive UUID to avoid new IID during kernel upgrade (#798)

Kernel's newer than 4.15 present /sys/dmi/id/product_uuid as a
lowercase value. Previously UUID was uppercase.

Azure datasource reads the product_uuid directly as their platform's
instance-id. This presents a problem if a kernel is either
upgraded or downgraded across the 4.15 kernel version boundary because
the case of the UUID will change, resulting in cloud-init seeing a
"new" instance id and re-running all modules.

Re-running cc_ssh in cloud-init deletes and regenerates ssh_host keys
on a system which can cause concern on long-running instances that
somethingnefarious has happened.

Also add:
- An integration test for this for Azure Bionic Ubuntu FIPS upgrading from
   a FIPS kernel with uppercase UUID to a lowercase UUID in linux-azure
- A new pytest.mark.sru_next to collect all integration tests related to our
   next SRU

LP: #1835584

1 files changed, 10 insertions, 2 deletions

diff --git a/cloudinit/sources/DataSourceAzure.py b/cloudinit/sources/DataSourceAzure.py
index 090dd66b..748a9716 100755
--- a/cloudinit/sources/DataSourceAzure.py
+++ b/cloudinit/sources/DataSourceAzure.py
@@ -683,10 +683,18 @@ class DataSourceAzure(sources.DataSource):
     def _iid(self, previous=None):
         prev_iid_path = os.path.join(
             self.paths.get_cpath('data'), 'instance-id')
-        iid = dmi.read_dmi_data('system-uuid')
+        # Older kernels than 4.15 will have UPPERCASE product_uuid.
+        # We don't want Azure to react to an UPPER/lower difference as a new
+        # instance id as it rewrites SSH host keys.
+        # LP: #1835584
+        iid = dmi.read_dmi_data('system-uuid').lower()
         if os.path.exists(prev_iid_path):
             previous = util.load_file(prev_iid_path).strip()
-            if is_byte_swapped(previous, iid):
+            if previous.lower() == iid:
+                # If uppercase/lowercase equivalent, return the previous value
+                # to avoid new instance id.
+                return previous
+            if is_byte_swapped(previous.lower(), iid):
                 return previous
         return iid