Manifest file - security

http://bazaar.launchpad.net/~click-hackers/click/trunk/view/head:/doc/file-format.rst discusses the manifest file format for click packages in general. This page discusses the format of the security JSON manifest used by aa-easyprof and how to integrate these easyprof manifests into click and traditional packaging. The aa-easyprof manifest contains a toplevel 'security' key, and the 'security' object is a dictionary with currently only one key defined: 'profiles'. The profiles object is a dictionary each of its keys being the name of a profile object (also a dictionary). The aa-easyprof tool looks at the security dictionary of the manifest to generate an AppArmor profile. For more details on aa-easyprof, see man 8 aa-easyprof. An example manifest representing all possible keys is:

{
  "security": {
    "profiles": {
      "com.example.foo": {
        "abstractions": [
          "audio",
          "gnome"
        ],
        "author": "Your Name",
        "binary": "/opt/foo/**",
        "comment": "Unstructured single-line comment",
        "copyright": "Unstructured single-line copyright statement",
        "name": "My Foo App",
        "policy_groups": [
          "networking",
          "user-application"
        ],
        "policy_vendor": "somevendor",
        "policy_version": 1.0,
        "read_path": [
          "/tmp/foo_r",
          "/tmp/bar_r/"
        ],
        "template": "user-application",
        "template_variables": {
          "APPNAME": "foo",
          "APPVERSION": "0.1",
          "VAR1": "bar",
          "VAR2": "baz"
        },
        "write_path": [
          "/tmp/foo_w",
          "/tmp/bar_w/"
        ]
      }
    }
  }
}

Security keys

aa-easyprof is a general purpose tool and all of the keys within a profile object are optional.

• profile name: keys to the 'profiles' dictionary are the profile names for each profile object. Therefore in the above example, "com.example.foo" is the profile name and the contents of the "com.example.foo" dictionary represent the profile. The profile name may specify the normalized absolute path to the binary (with AARE (see apparmor.d(8)) or an name that consists only of lower case letters (a-z), upper case letters (A-Z), digits (0-9), plus (+) and minus (-) signs, periods (.), colons (:), underscores (_) and tildes (~) (essentially a combination of the allowed characters for Ubuntu package names and versions, plus underscores)

• binary: path to binary for this policy when using path-based attachment. Should not be specified when the profile name is an absolute path

• author: author of the policy

• comment: comment for the policy

• copyright: copyright of the policy

• name: name of policy. If not specified, use the name of the binary. Note, this is not the AppArmor profile name.

• policy_vendor: vendor of policy groups and templates ([a-zA-Z_0-9\-\.])

• policy_version: version of the vendor policy (float)

• template: template to use ([a-zA-Z_0-9\-\.])

• template_variables: list of template variable assignments. Supported template variables are template-specific

• abstractions: list of AppArmor abstractions to include (typically from /etc/apparmor.d)

• policy_groups: list of AppArmor policy groups to include ([a-zA-Z_0-9\-\.])

• read_path: list of paths to allow read access

• write_path: list of paths to allow write access

Use in Ubuntu

Click

Click packages in Ubuntu are required to run under application confinement and therefore the click manifest file must contain a security manifest for each application. This is accomplished by using an AppArmor hook in the toplevel hooks object of the click manifest. The hooks object is a dictionary with keys that specify application names. These keys are themselves dictionaries with keys for each type of hook, such as "apparmor": "apparmor/myapp.json". For example, the click manifest might contain:

  {
    "name": "com.ubuntu.developer.username.myapp",
    "version": "0.1",
    ...
    "hooks": {
      "myapp": {
        "apparmor": "apparmor/myapp.json",
        ...
      },
      "myapp-camera": {
        "apparmor": "apparmor/myapp-camera.json",
        ...
      }
    }
  }

In this manner the apparmor hook specifies a separate security JSON manifest file associated with a specific application name (ie, 1 to 1 mapping such that the myapp application uses the apparmor/myapp.json security manifest and the myapp-camera uses the apparmor/myapp-camera.json security manifest). The click AppArmor hook looks at these separate security JSON manifests to generate AppArmor profiles via the aa-clicktool and aa-easyprof tools.

The click security manifests differ somewhat from the JSON format that would be given directly to the aa-easyprof tool. Specifically, the click AppArmor hook will setup some aa-easyprof fields automatically (such as policy_vendor). As such, some fields are required, some handled automatically, some unused and some are technically supported but dangerous and will red flag the package for manual review.

• Required fields for each profile object in the profiles dictionary of the security object:

  • JSON profile object (ie, the profile name key and its corresponding dictionary). In click on Ubuntu, the profile name should specify the name of the application that this profile is meant to protect. The only exception is if the profile name is used to specify path-based attachment (where the version of the app is expected to be part of the absolute path)

  • policy_groups - these are used to grant permissions to the app, such as networking, online accounts, content picking, etc. See aa-easyprof --policy-vendor=ubuntu --policy-version=1.0 --list-policy-groups for a complete list

  • policy_version should be set. 1.0 is the first supported Ubuntu policy version. For other versions, see /usr/share/apparmor/easyprof/templates/ubuntu/ and /usr/share/apparmor/easyprof/policygroups/ubuntu/

  • template - automatically set to ubuntu-sdk if not specified. See aa-easyprof --policy-vendor=ubuntu --policy-version=1.0 --list-templates (using the appropriate vendor version) for a list of other templates. NOTE: an "unconfined" template exists that provides very wide permissions to support special-case applications (ie, trusted applications that have been manually reviewed). Applications developers should not use this template (the upload will be rejected).

  • policy_vendor - automatically set to ubuntu

  • template_variables - automatically sets the following:

    • APPNAME - set to name from the toplevel click manifest (eg, "APPNAME": "com.ubuntu.developer.username.myapp")

    • APPVERSION - set to version from the toplevel click manifest (eg, "APPVERSION": "0.1")

    These template variables are used to differentiate application paths. Eg, the resulting AppArmor policy will have something like:

     @{APPNAME}="com.ubuntu.developer.username.myapp"
     @{APPVERSION}="0.1"
     ...
       /opt/click.ubuntu.com/@{APPNAME}/@{APPVERSION}/    r,
       /opt/click.ubuntu.com/@{APPNAME}/@{APPVERSION}/**  r,
       /opt/click.ubuntu.com/@{APPNAME}/@{APPVERSION}/**/ r,

• Unused/ignored
  • name
  • author
  • comment
  • copyright
• Red-flagged for manual review (use should actively be discouraged with updates made to policy groups and templates)
  • abstractions
  • read_path
  • write_path

  • binary may be set as a recursive glob on the toplevel installation directory. Eg, if the app is installed to /opt/com.ubuntu.developer/com.ubuntu.developer.username.myapp, then binary could be legitimately set to /opt/com.ubuntu.developer/com.ubuntu.developer.username.myapp/**. Not typically necessary

  • template set to "unconfined". This almost always will result in rejection of the package

Furthermore, because separate security manifests are used per application, the toplevel security, profiles and profile name objects are omitted from the security manifest. For example, putting it all together, the click manifest and security manifests for myapp and myapp-camera might be:

$ cat manifest.json
  {
    "name": "com.ubuntu.developer.username.myapp",
    "version": "0.1",
    ...
    "hooks": {
      "myapp": {
        "apparmor": "apparmor/myapp.json",
        ...
      },
      "myapp-camera": {
        "apparmor": "apparmor/myapp-camera.json",
        ...
      }
    }
  }

$ cat apparmor/myapp.json
 {
   "policy_groups": [
     "networking"
   ],
   "policy_version": 1.0
 }

$ cat apparmor-camera/myapp.json
 {
   "policy_groups": [
     "camera",
     "location"
   ],
   "policy_version": 1.0
 }

NOTE: click supports multiple versions of an application installed on the system such that one user has one version installed, and another user has another version installed. Because we then need versioned profile names and filenames for the profiles, the AppArmor click hook will generate a versioned profile name in the form of: $name_$application_$version. Therefore, with the above manifests, the two profile names are:

• com.ubuntu.developer.username.myapp_myapp_0.1
• com.ubuntu.developer.username.myapp_myapp-camera_0.1

such that when the application is installed, the click apparmor hook will create two profiles in the AppArmor profiles directory with these names. This preserves namespacing in the kernel profile names and the profile filenames while reducing complexity in the manifest file itself.

Unconfined apps are supported via the "unconfined" template.

Traditional packaging

Traditional packaging can also leverage aa-easyprof, but the process is slightly more involved. In general, the following need to happen (see man dh_apparmor for details):

• the security manifest file should use the standard aa-easyprof structure (ie, with the security, profile and profile name dictionaries). It should be added to debian/. Because traditional packaging has different governance rules for including in a distribution, the manifest may contain any of the supported fields. For example:

   {
     "security": {
       "profiles": {
         "traditional-app1": {
           "abstractions": [
             "nameservice"
           ],
           "policy_groups": [
             "user-application"
           ],
           "template": "user-application",
           "template_variables": {
             "APPNAME": "traditional-app1"
           }
         }
       }
     }
   }

• aa-easyprof is given the manifest file to generate a profile
• the profile is installed into a package

• the postinst loads the AppArmor policy into the kernel

The process is made easier with dh_apparmor. Create a manifest file following the above instructions for required fields (note that you must fill in the automatic ones yourself when not using click packaging) then:

1. put the manifest file in debian/manifest.json

2. adjust debian/control to Build-Depends on dh-apparmor >= 2.8.0-0ubuntu14

3. update debian/rules to call dh_apparmor. Eg:

   override_dh_install:
           dh_apparmor -p<deb binary> --profile-name=<profile name from the manifest> --manifest=security-manifest.json
           dh_install

   and then to clean up:

   override_dh_clean:
           dh_clean
           rm -rf debian/apparmor

4. install the files. Eg, add to debian/<deb binary>.install:

   debian/apparmor/<profile name> etc/apparmor.d

The remaining consideration is making sure that the app runs confined. You'll know you have it right if when the application is running, the output of aa-status shows that the application is confined. If the application provides an executable (eg, ELF binary, executable python script), then specifying the 'binary' in the manifest is enough. If instead a helper such as qmlscene is being used, there are several choices:

• use the new Ubuntu application lifecycle and start the application via an Upstart job (preferred, pending but not available as of 2013/07/12)

• add XCanonicalAppArmorProfile=<profile name> to the .desktop file until Ubuntu application lifecycle is finished (not available as of 2013/07/12)

• update the .desktop file so use aa-exec -p <profile name> ... in the Exec line. This will work once LP: #1200437 is fixed (pending)

• Create a shell script to use aa-exec -p <profile name> ... and have the .desktop file use Exec=<path to shell script>

Bugs

When filing bugs dealing with the manifest file or resulting permissions, please use one of the below and use the 'application-confinement' tag:

• Bugs against AppArmor policy for SDK applications

• General bugs against aa-easyprof

• Policy bugs that should be resolved in the SDK