Fix leading slashes being stripped from mount src (#24013)

* Tidy mount module for testing

Fix spelling mistakes in comments. I *think* the example for omitting parents
root has the wrong parent ID.

Make mountinfo file a parameter for testing.

* Don't strip leading slash from mounts

The current code does not follow the example, it produces src=tmp/aaa instead
of src=/tmp/aaa. This causes problems with bind mounts under /rootfs.

* Use dictionary to store mounts by ID

Instead of looping over each one to check if the ID matches. This does not
preserve the order of the output on < Python3.6, but that is not necessary.

* Make linux_mounts a dict

Always accessed by 'dst', so avoid looping by just making it a key.

* Add test case for get_linux_mounts

lib/ansible/modules/system/mount.py

@@ -446,19 +446,12 @@ def is_bind_mounted(module, linux_mounts, dest, src=None, fstype=None):
     if get_platform() == 'Linux' and linux_mounts is not None:
         if src is None:
             # That's for unmounted/absent
-            for m in linux_mounts:
-                if m['dst'] == dest:
+            if dest in linux_mounts:
                 is_mounted = True
         else:
-            mounted_src = None
+            if dest in linux_mounts:
+                is_mounted = linux_mounts[dest]['src'] == src
 
-            for m in linux_mounts:
-                if m['dst'] == dest:
-                    mounted_src = m['src']
-
-            # That's for mounted
-            if mounted_src is not None and mounted_src == src:
-                is_mounted = True
     else:
         bin_path = module.get_bin_path('mount', required=True)
         cmd = '%s -l' % bin_path
@@ -483,11 +476,9 @@ def is_bind_mounted(module, linux_mounts, dest, src=None, fstype=None):
     return is_mounted
 
 
-def get_linux_mounts(module):
+def get_linux_mounts(module, mntinfo_file="/proc/self/mountinfo"):
     """Gather mount information"""
 
-    mntinfo_file = "/proc/self/mountinfo"
-
     try:
         f = open(mntinfo_file)
     except IOError:
@@ -500,7 +491,7 @@ def get_linux_mounts(module):
     except IOError:
         module.fail_json(msg="Cannot close file %s" % mntinfo_file)
 
-    mntinfo = []
+    mntinfo = {}
 
     for line in lines:
         fields = line.split()
@@ -515,27 +506,23 @@ def get_linux_mounts(module):
             'src': fields[-2]
         }
 
-        mntinfo.append(record)
+        mntinfo[record['id']] = record
 
-    mounts = []
-
-    for mnt in mntinfo:
-        src = mnt['src']
+    mounts = {}
 
-        if mnt['parent_id'] != 1:
-            # Find parent
-            for m in mntinfo:
-                if mnt['parent_id'] == m['id']:
+    for mnt in mntinfo.values():
+        if mnt['parent_id'] != 1 and mnt['parent_id'] in mntinfo:
+            m = mntinfo[mnt['parent_id']]
             if (
                     len(m['root']) > 1 and
                     mnt['root'].startswith("%s/" % m['root'])):
                 # Ommit the parent's root in the child's root
                 # == Example:
-                        # 204 136 253:2 /rootfs / rw - ext4 /dev/sdb2 rw
+                # 140 136 253:2 /rootfs / rw - ext4 /dev/sdb2 rw
                 # 141 140 253:2 /rootfs/tmp/aaa /tmp/bbb rw - ext4 /dev/sdb2 rw
                 # == Expected result:
                 # src=/tmp/aaa
-                        mnt['root'] = mnt['root'][len(m['root']) + 1:]
+                mnt['root'] = mnt['root'][len(m['root']):]
 
             # Prepend the parent's dst to the child's root
             # == Example:
@@ -545,10 +532,9 @@ def get_linux_mounts(module):
             # src=/tmp/aaa
             if m['dst'] != '/':
                 mnt['root'] = "%s%s" % (m['dst'], mnt['root'])
-
             src = mnt['root']
-
-                    break
+        else:
+            src = mnt['src']
 
         record = {
             'dst': mnt['dst'],
@@ -557,7 +543,7 @@ def get_linux_mounts(module):
             'fs': mnt['fs']
         }
 
-        mounts.append(record)
+        mounts[mnt['dst']] = record
 
     return mounts
 
@@ -618,7 +604,7 @@ def main():
     linux_mounts = []
 
     # Cache all mounts here in order we have consistent results if we need to
-    # call is_bind_mouted() multiple times
+    # call is_bind_mounted() multiple times
     if get_platform() == 'Linux':
         linux_mounts = get_linux_mounts(module)
 

test/units/modules/system/test_linux_mountinfo.py

@@ -0,0 +1,25 @@
+import os
+import tempfile
+
+from ansible.compat.tests import unittest
+from ansible.module_utils._text import to_bytes
+
+from ansible.modules.system.mount import get_linux_mounts
+
+
+class LinuxMountsTestCase(unittest.TestCase):
+
+    def _create_file(self, content):
+        tmp_file = tempfile.NamedTemporaryFile(prefix='ansible-test-', delete=False)
+        tmp_file.write(to_bytes(content))
+        tmp_file.close()
+        self.addCleanup(os.unlink, tmp_file.name)
+        return tmp_file.name
+
+    def test_code_comment(self):
+        path = self._create_file(
+            '140 136 253:2 /rootfs / rw - ext4 /dev/sdb2 rw\n'
+            '141 140 253:2 /rootfs/tmp/aaa /tmp/bbb rw - ext4 /dev/sdb2 rw\n'
+        )
+        mounts = get_linux_mounts(None, path)
+        self.assertEqual(mounts['/tmp/bbb']['src'], '/tmp/aaa')