[policies] Fix bug in distro identification

Fixes a bug in #3764.

A bug in the distro-identifying logic caused incorrect identification
of the distro as CentOS, Fedora, or RHEL under the following conditions:

1. Distro inherits RedHatPolicy
2. Distro has either of /etc/{centos,fedora,redhat}-release
3. Policy file appears earlier than redhat.py in dictionary order

The issue occurs because the distro-identifying logic relies on the
existence of the above os_release_file without examining its contents,
more than checking NAME or ID in the /etc/os-release file. As a result,
once /etc/{centos,fedora,redhat}-release is found, the contents of
/etc/os-release are never checked, leading to distro misidentification.

At least AlmaLinux is affected by this bug.

Signed-off-by: Koichiro Iwao <[email protected]>

sos/policies/distros/__init__.py

@@ -164,7 +164,10 @@ def _check_release(content):
         if remote:
             return _check_release(remote)
         # use the os-specific file primarily
-        if os.path.isfile(cls.os_release_file):
+        # also check the symlink destination
+        if (os.path.isfile(cls.os_release_file) and
+            os.path.basename(cls.os_release_file)
+                == os.path.basename(os.path.realpath(cls.os_release_file))):
             return True
         # next check os-release for a NAME or ID value we expect
         with open(OS_RELEASE, "r", encoding='utf-8') as f: