DataSourceOVF: use util.find_devs_with(TYPE=iso9660)

DataSourceOVF attempts to find iso files via walking os.listdir('/dev/')
which is far too wide.  This approach is too invasive and can sometimes
race with systemd attempting to fsck and mount devices.

Instead, utilize cloudinit.util.find_devs_with to filter devices by
criteria (which uses blkid under the covers).  This results in fewer
attempts to mount block devices which do not contain iso filesystems.

Unittest changes include:
- cloudinit.tests.helpers; introduce add_patch() helper
- Add unittest coverage for DataSourceOVF use of transport_iso9660

LP: #1718287

1 files changed, 47 insertions, 27 deletions

diff --git a/cloudinit/sources/DataSourceOVF.py b/cloudinit/sources/DataSourceOVF.py
index 24b45d55..ccebf11a 100644
--- a/cloudinit/sources/DataSourceOVF.py
+++ b/cloudinit/sources/DataSourceOVF.py
@@ -375,26 +375,56 @@ def get_ovf_env(dirname):
     return (None, False)
 
 
-# Transport functions take no input and return
-# a 3 tuple of content, path, filename
-def transport_iso9660(require_iso=True):
+def maybe_cdrom_device(devname):
+    """Test if devname matches known list of devices which may contain iso9660
+       filesystems.
 
-    # default_regex matches values in
-    # /lib/udev/rules.d/60-cdrom_id.rules
-    # KERNEL!="sr[0-9]*|hd[a-z]|xvd*", GOTO="cdrom_end"
-    envname = "CLOUD_INIT_CDROM_DEV_REGEX"
-    default_regex = "^(sr[0-9]+|hd[a-z]|xvd.*)"
+    Be helpful in accepting either knames (with no leading /dev/) or full path
+    names, but do not allow paths outside of /dev/, like /dev/foo/bar/xxx.
+    """
+    if not devname:
+        return False
+    elif not isinstance(devname, util.string_types):
+        raise ValueError("Unexpected input for devname: %s" % devname)
+
+    # resolve '..' and multi '/' elements
+    devname = os.path.normpath(devname)
 
-    devname_regex = os.environ.get(envname, default_regex)
+    # drop leading '/dev/'
+    if devname.startswith("/dev/"):
+        # partition returns tuple (before, partition, after)
+        devname = devname.partition("/dev/")[-1]
+
+    # ignore leading slash (/sr0), else fail on / in name (foo/bar/xvdc)
+    if devname.startswith("/"):
+        devname = devname.split("/")[-1]
+    elif devname.count("/") > 0:
+        return False
+
+    # if empty string
+    if not devname:
+        return False
+
+    # default_regex matches values in /lib/udev/rules.d/60-cdrom_id.rules
+    # KERNEL!="sr[0-9]*|hd[a-z]|xvd*", GOTO="cdrom_end"
+    default_regex = r"^(sr[0-9]+|hd[a-z]|xvd.*)"
+    devname_regex = os.environ.get("CLOUD_INIT_CDROM_DEV_REGEX", default_regex)
     cdmatch = re.compile(devname_regex)
 
+    return cdmatch.match(devname) is not None
+
+
+# Transport functions take no input and return
+# a 3 tuple of content, path, filename
+def transport_iso9660(require_iso=True):
+
     # Go through mounts to see if it was already mounted
     mounts = util.mounts()
     for (dev, info) in mounts.items():
         fstype = info['fstype']
         if fstype != "iso9660" and require_iso:
             continue
-        if cdmatch.match(dev[5:]) is None:  # take off '/dev/'
+        if not maybe_cdrom_device(dev):
             continue
         mp = info['mountpoint']
         (fname, contents) = get_ovf_env(mp)
@@ -406,29 +436,19 @@ def transport_iso9660(require_iso=True):
     else:
         mtype = None
 
-    devs = os.listdir("/dev/")
-    devs.sort()
+    # generate a list of devices with mtype filesystem, filter by regex
+    devs = [dev for dev in
+            util.find_devs_with("TYPE=%s" % mtype if mtype else None)
+            if maybe_cdrom_device(dev)]
     for dev in devs:
-        fullp = os.path.join("/dev/", dev)
-
-        if (fullp in mounts or
-                not cdmatch.match(dev) or os.path.isdir(fullp)):
-            continue
-
-        try:
-            # See if we can read anything at all...??
-            util.peek_file(fullp, 512)
-        except IOError:
-            continue
-
         try:
-            (fname, contents) = util.mount_cb(fullp, get_ovf_env, mtype=mtype)
+            (fname, contents) = util.mount_cb(dev, get_ovf_env, mtype=mtype)
         except util.MountFailedError:
-            LOG.debug("%s not mountable as iso9660", fullp)
+            LOG.debug("%s not mountable as iso9660", dev)
             continue
 
         if contents is not False:
-            return (contents, fullp, fname)
+            return (contents, dev, fname)
 
     return (False, None, None)