SnappyConfinement
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| * '''Contributors''': [[LaunchpadHome:jdstrand|Jamie Strandboge]], [[LaunchpadHome:mdeslaur|Marc Deslauriers]] * '''Packages affected''': apparmor, apparmor-easyprof-ubuntu-snappy, click-apparmor, snappy-systemd * '''Status''': Alpha |
* '''Contributors''': [[LaunchpadHome:jdstrand|Jamie Strandboge]], [[LaunchpadHome:tyhicks|Tyler Hicks]] * '''Packages affected''': apparmor, libseccomp, ubuntu-core-security, ubuntu-snappy, ubuntu-core-launcher (historically, click-apparmor) * '''Status''': Production |
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| Snappy confinement is an evolution of the [[https://wiki.ubuntu.com/SecurityTeam/Specifications/ApplicationConfinement|security model for Ubuntu Touch]]. The basic concepts for confined applications and the !AppStore model pertain to snappy applications as well. In short, applications are confined using AppArmor by default and this is achieved through a simple template-based system where policy is extended through the use of policy groups. | Snappy confinement is an evolution of the [[https://wiki.ubuntu.com/SecurityTeam/Specifications/ApplicationConfinement|security model for Ubuntu Touch]]. The basic concepts for confined applications and the !AppStore model pertain to snappy applications as well. In short, applications are confined by default through the use of various technologies and this is achieved through a simple template-based system where policy is extended through the use of interfaces. |
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| It will be most helpful if you are familiar with: * http://www.ubuntu.com/snappy#core-tour * http://developer.ubuntu.com/snappy/filesystem-layout/ * http://developer.ubuntu.com/snappy/packaging-format-for-apps/ |
Please see the security whitepaper for the most up to date information on Ubuntu Core series 16: https://developer.ubuntu.com/en/snappy/guides/security-whitepaper/ (starting at section 'Snappy for Ubuntu Core') |
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| == Implementation summary == Snappy uses a simple packaging format that is an evolution of [[https://wiki.ubuntu.com/SecurityTeam/Specifications/ApplicationConfinement/Manifest|click packaging]]. Snappy packages use a declarative [[http://developer.ubuntu.com/snappy/packaging-format-for-apps/|yaml syntax]] and defaults to using `default` !AppArmor template and the "networking" policy group. Apps may customize the default behavior in a number of ways via the yaml syntax. |
Ubuntu Core 15.04 spec can be viewed here: https://wiki.ubuntu.com/SecurityTeam/Specifications/SnappyConfinement15.04 |
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| Under the hood, the [[https://wiki.ubuntu.com/SecurityTeam/Specifications/ApplicationConfinement/Manifest|security manifest]] is used to describe the confinement of the app. Most apps do not need to specify anything for confinement and snappy will create a security manifest like the following:{{{ { "policy_vendor": "ubuntu-snappy", "policy_version": 1.3, "template": "default", "policy_groups": [ "networking" ] } |
The most up to date information on snappy confinement can be found here: https://github.com/snapcore/snapd/wiki/Security == Debugging == When debugging policy issues, the `snappy-debug.security` tool can help. Use `sudo snap install snappy-debug` and then simply launch it to have it follow the logs and provide suggestions:{{{ $ sudo snap install snappy-debug $ sudo snap connect snappy-debug:log-observe ubuntu-core:log-observe $ sudo /snap/bin/snappy-debug.security scanlog ... |
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| The defaults provided may change as the confinement needs evolve. The template policy is found in `/usr/share/apparmor/easyprof/ubuntu-snappy/templates/1.3/default` and the `networking` policy is found in `/usr/share/apparmor/easyprof/ubuntu-snappy/policy-groups/1.3/networking`. | `snappy-debug.security scanlog` will report both !AppArmor and seccomp denials. |
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| === "apparmor" === Security policy in snappy is done through `apparmor` integration. Internally `apparmor` integration generates an !AppArmor profile based on what is in the snappy packaging yaml. Importantly, the !AppArmor profile name is unique to the application binary/service and is achieved by using the concept of an ApplicationId. The APP_ID is the composition of the package name, the service/binary name and package version. The APP_ID takes the form of `<pkgname>_<appname>_<version>`. For example, if this is in packaging yaml:{{{ name: foo version: 0.1 ... services: - name: bar start: bin/bar ports: required: 80/tcp |
Alternatively you can use the lowlevel tools to check to see if you have any denials:{{{ $ sudo journalctl --no-pager -k | grep audit |
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| Then the APP_ID for the 'bar' service is `foo_bar_0.1`. Applications are launched under confinement through the following: * If unspecified in the packaging yaml, `snappy` will choose the `default` profile and `networking` policy group (this may change as snappy involves) * Apps may choose to specify an alternate confinement binaries and services by specifying `security-template` and/or `security-policy-groups` in the yaml. Eg:{{{ ... services: - name: bar start: bin/bar ports: required: 80/tcp security-template: nondefault security-policy-groups: networking, something, etc }}} * For special circumstances, the packaging yaml may also use `apparmor` in its 'integration' section:{{{ ... services: - name: bar start: bin/bar ports: required: 80/tcp integration: bar: apparmor: meta/bar.apparmor }}} * `aa-clickhook` is run on package install and places the resulting profile in `/var/lib/apparmor/profiles`. * If the binary is a service, the `snappy-systemd` makes sure `/etc/systemd/system/<service>.service` has `AppArmorProfile=<profilename>` (in the above example, `AppArmorProfile=foo_bar_0.1`) such that the service starts under confinement. * If the binary is a cli binary, it can be launched under confinement via the `bin-path` mechanism (see below) * apparmor policy templates and policy groups are usually shipped via the apparmor-easyprof-ubuntu-snappy package The default template allows ELF executables, python, perl and shell (with selected corresponding utilities from /bin and /usr/bin), disallows capabilities(7) and enforces application isolation as per the [[http://developer.ubuntu.com/snappy/filesystem-layout/|snappy FHS]]. === "apparmor-profile" === In addition to the above, specialized, hand-crafted confinement may be done via the `apparmor-profile` integration section. Specifying `apparmor-profile` will trigger a manual review in the store, and is not needed for normal Snappy apps, but instead is provided for snappy framework and trusted snappy applications. The `aa-profile-hook` works similarly to `aa-clickhook`: * The snappy packaging specifies to use 'apparmor-profile' in its 'integration' section, which specifies the profile. Eg:{{{ ... services: - name: bar start: bin/bar ports: required: 80/tcp integration: bar: apparmor-profile: meta/bar.profile }}} * the profile should reference the !AppArmor variables for CLICK_DIR, APP_PKGNAME, APP_APPNAME, APP_VERSION and for profile attachment, just like the `apparmor` template does with click-apparmor * aa-profile-hook is run on install and places the profile in `/var/lib/apparmor/profiles` (prefixed with 'profile_') * If the binary is a service, the `snappy-systemd` makes sure `/etc/systemd/system/<service>.service` has `AppArmorProfile=<profilename>` (in the above example, `AppArmorProfile=foo_bar_0.1`) such that the service starts under confinement. * `aa-profile-hook` is shipped in click-apparmor * use of `apparmor-profile` requires manual review via the store. To improve maintenace, the profile author can use !AppArmor variables to avoid worrying about updating the profile name, the app name, where the app is installed or knowing the package version. Example profile:{{{ #include <tunables/global> # Specified profile variables ###VAR### ###PROFILEATTACH### (attach_disconnected) { #include <abstractions/base> #include <abstractions/nameservice> # Read-only for the install directory @{CLICK_DIR}/@{APP_PKGNAME}/ r, @{CLICK_DIR}/@{APP_PKGNAME}/@{APP_VERSION}/ r, @{CLICK_DIR}/@{APP_PKGNAME}/@{APP_VERSION}/** mrklix, # Writable home area owner @{HOMEDIRS}/apps/@{APP_PKGNAME}/ rw, owner @{HOMEDIRS}/apps/@{APP_PKGNAME}/** mrwklix, # Read-only system area for other versions /var/lib/apps/@{APP_PKGNAME}/ r, /var/lib/apps/@{APP_PKGNAME}/** mrkix, # Writable system area only for this version. /var/lib/apps/@{APP_PKGNAME}/@{APP_VERSION}/ w, /var/lib/apps/@{APP_PKGNAME}/@{APP_VERSION}/** wl, ... specialized confinement ... }}} Example yaml to use the profile:{{{ name: foo version: 0.1 ... services: - name: bar start: bin/bar ports: required: 80/tcp integration: bar: apparmor-profile: meta/bar.profile }}} You may not specify the `apparmor` and `apparmor-profile` for the same <appname> (eg, specifying `"apparmor-profile": "meta/appname.profile"` and `"apparmor": "meta/appname.apparmor"` is an error). === "apparmor-policy" === `apparmor-policy` is provided for frameworks to extend security policy (specifically, to add templates and/or policy groups) so that apps that specify the framework may then reference these template/policy groups to access any services/binaries that the framework exposes. Key ideas for snappy frameworks: * Frameworks extend Ubuntu Core in useful ways for apps to use * Frameworks are delivered via snaps * Because frameworks require additional privilege and are considered trusted (how much depends on what the framework offers), framework authors must partner with Canonical on framework design, security policy verification, acceptance in the store, etc * Frameworks are expected to provide significant functionality that is useful to a wide range of apps * Multiple snappy frameworks may be installed on the same system * The number of snappy frameworks is expected to be relatively low See the SnappyFrameworkConfinement for more details. === "bin-path" === If the yaml specifies 'binaries' then `bin-path` will expose these binaries to the shell and other apps by launching apps via a specialized launcher that does the following: * chdir()s to the app install directory * sets miscellaneous environment variables * sets up and mount namespace and in that mount namespace, setup a root overlay and /tmp * sets up cgroup net_cls for tagging all packets for this app * sets up a cgroup for net_cls named foo_bar_0.1 for tagging all packets for this app * sets up iptables chain in 'security' table for the app (uses 'snapps' chain, then app-specific subchains) and add rules to allow from specified apps, and disallow from untagged) * apply seccomp rules to only allow binding to specified ports * launches the app under confinement It does this by adding a symlink to a directory in your PATH which points to the launcher. The launcher then calculates the APP_ID to launch the app under. This launcher will setup the environment, adjust the working directory and launch the binary under its !AppArmor profile. For example, consider the following snappy packaging yaml:{{{ name: foo version: 0.1 ... binaries: - name: bin/bar }}} `bin-path` will create the `foo/bar` symlink in a directory in your PATH (creating the 'foo' directory as needed. Also, notice this is <name>/<basename of binary name>). When executing that symlink, the launcher will: * chdir() to /apps/foo/current * set miscellaneous environment variables * set up and mount namespace and in that mount namespace, setup a root overlay and /tmp * set up a cgroup for net_cls named foo_bar_0.1 for tagging * set up iptables chain in 'security' table for the app and add rules to allow from specified apps, and disallow from untagged * apply seccomp rules to only allow binding to specified ports * run the app under the `foo_bar_0.1` profile Note, as of 2014-12-09, a shell script is temporarily being used instead of a symlink. == Normal usage == As stated, the snappy packaging yaml does not have to do anything to specify the default confinement. Eg, the following yaml:{{{ name: foo version: 0.1 ... services: - name: bar start: bin/bar - name: baz start: bin/baz - name: norf start: bin/norf }}} will create the following !AppArmor profiles with default confinement: * foo_bar_0.1 * foo_baz_0.1 * foo_norf_0.1 == Advanced usage == While the snappy packaging yaml is intentionally simple and straightforward for app developers, it can also quite flexible for those who need it. For example, consider the following yaml:{{{ name: foo version: 0.1 ... services: - name: normal-service start: bin/normal-service - name: extra-policy-group-service start: bin/extra-policy-group-service security-policy-groups: networking, extra - name: non-default-template-service start: bin/non-default-template-service security-template: non-default binaries: - name: bin/normal-binary - name: extra-policy-group-binary security-policy-groups: networking, extra }}} snappy will generate the following security manifests: * normal-service:{{{ { "policy_vendor": "ubuntu-snappy", "policy_version": 1.3, "template": "default", "policy_groups": [ "networking" ] } }}} * extra-policy-group-service:{{{ { "policy_vendor": "ubuntu-snappy", "policy_version": 1.3, "template": "default", "policy_groups": [ "networking", "extra" ] } }}} * non-default-template-service:{{{ { "policy_vendor": "ubuntu-snappy", "policy_version": 1.3, "template": "non-default", "policy_groups": [ "networking" ] } }}} * normal-binary:{{{ { "policy_vendor": "ubuntu-snappy", "policy_version": 1.3, "template": "default", "policy_groups": [ "networking" ] } }}} * extra-policy-group-binary:{{{ { "policy_vendor": "ubuntu-snappy", "policy_version": 1.3, "template": "default", "policy_groups": [ "networking", "extra" ] } }}} Which in turn creates the following !AppArmor profiles: * foo_normal-service_0.1 * foo_extra-policy-group-service_0.1 * foo_non-default-template-service_0.1 * foo_normal-binary_0.1 * foo_extra-policy-group-binary_0.1 == Debugging == To check to see if you have any denials:{{{ $ sudo journalctl --no-pager -k | grep DEN }}} A denial will look something like:{{{ |
An !AppArmor denial will look something like:{{{ |
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| If there are no denials, !AppArmor shouldn't be blocking the app. | If there are no !AppArmor denials, !AppArmor shouldn't be blocking the app. |
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| If there are denials, you can unblock yourself by: * modifying the profile in /var/lib/apparmor/profiles that corresponds to your app |
If there are !AppArmor denials, you can unblock yourself by: * modifying the profile in /var/lib/snapd/apparmor/profiles that corresponds to your app |
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| $ sudo apparmor_parser -r /var/lib/apparmor/profiles/<profile> | $ sudo apparmor_parser -r /var/lib/snapd/apparmor/profiles/<profile> |
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A seccomp denial will look something like:{{{ audit: type=1326 audit(1430766107.122:16): auid=1000 uid=1000 gid=1000 ses=15 pid=1491 comm="env" exe="/bin/bash" sig=31 arch=40000028 syscall=983045 compat=0 ip=0xb6fb0bd6 code=0x0 }}} The `syscall=983045` can be resolved with the `scmp_sys_resolver` command (you may also use the `sc-logresolve` command). Eg:{{{ $ scmp_sys_resolver 983045 set_tls }}} In general, if there are no seccomp denials, it shouldn't be blocking the app, however do keep in mind that if the app is somehow trying to elevate its privileges (eg, via a setuid executable) the app may receive a `Permission denied` error with no denial (see `PR_SET_NO_NEW_PRIVS` discussion above). If there are seccomp denials, you can unblock yourself by modifying the seccomp file in /var/lib/snapd/seccomp/profiles, then launch your app like normal (the launcher will pick up the change on app invocation). |
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| * `sudo aa-clickhook -f` will regenerate all the `apparmor` profiles in /var/lib/apparmor/profiles * `sudo aa-profile-hook -f` will regenerate all the `apparmor-profile` profiles in /var/lib/apparmor/profiles * `sudo aa-status` will show you the profiles loaded in the kernel and what processes are running under them * `ps Z`, `ps Z <pid>` and `ps auxwwZ` will show you normal ps output, but with the apparmor label the profile is running under * `sudo systemctl stop <app>.service` and `sudo systemctl start <app>.service` to stop and start services from /etc/systemd/system (ie, where snappy-systemd puts the service files) |
* `sudo sysctl -w kernel.printk_ratelimit=0` will disable kernel rate limitingof denials * `snappy-debug.security scanlog`: follow /var/log/syslog` and show !AppArmor and seccompg denial * `snappy-debug.security disable-rate-limiting`: disable kernel rate limiting * `snappy-debug.security reload [<name>.<origin>]`: reloads apparmor security policy into the kernel * `snappy-debug.security regenerate [<name>.<origin>]`: regenerate apparmor security policy from snappy packaging |
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| * In one terminal launch (tail kernel log for !AppArmor denials):{{{ $ sudo journalctl -f -k | grep DEN |
* In one terminal launch `snappy-debug.security scanlog`:{{{ $ sudo snappy-debug.security scanlog |
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| * In another (service name is the filename in /etc/systemd/system):{{{ $ sudo journalctl -f -u <service name> |
* In another (if daemon):{{{ $ sudo journalctl -k -u <service name>| grep audit |
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| * Then launch the app with systemctl like above, or launch manually under confinement with:{{{ | * Then launch the app normally or launch manually under confinement with:{{{ |
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| = Future work = * Confining snappy apps (particularly processes requiring root) may use !AppArmor-wrapped user namespaces. |
Created: 2014-12-05
Created by: Jamie Strandboge
Contributors: Jamie Strandboge, Tyler Hicks
Packages affected: apparmor, libseccomp, ubuntu-core-security, ubuntu-snappy, ubuntu-core-launcher (historically, click-apparmor)
Status: Production
Introduction
Snappy confinement is an evolution of the security model for Ubuntu Touch. The basic concepts for confined applications and the AppStore model pertain to snappy applications as well. In short, applications are confined by default through the use of various technologies and this is achieved through a simple template-based system where policy is extended through the use of interfaces.
Please see the security whitepaper for the most up to date information on Ubuntu Core series 16: https://developer.ubuntu.com/en/snappy/guides/security-whitepaper/ (starting at section 'Snappy for Ubuntu Core')
Ubuntu Core 15.04 spec can be viewed here: https://wiki.ubuntu.com/SecurityTeam/Specifications/SnappyConfinement15.04
The most up to date information on snappy confinement can be found here: https://github.com/snapcore/snapd/wiki/Security
Debugging
When debugging policy issues, the snappy-debug.security tool can help. Use sudo snap install snappy-debug and then simply launch it to have it follow the logs and provide suggestions:
$ sudo snap install snappy-debug $ sudo snap connect snappy-debug:log-observe ubuntu-core:log-observe $ sudo /snap/bin/snappy-debug.security scanlog ...
snappy-debug.security scanlog will report both AppArmor and seccomp denials.
Alternatively you can use the lowlevel tools to check to see if you have any denials:
$ sudo journalctl --no-pager -k | grep audit
An AppArmor denial will look something like:
apparmor="DENIED" operation="mkdir" profile="foo_bar_0.1" name="/var/lib/foo" pid=637 comm="bar" requested_mask="c" denied_mask="c" fsuid=0 ouid=0
If there are no AppArmor denials, AppArmor shouldn't be blocking the app.
If there are AppArmor denials, you can unblock yourself by:
- modifying the profile in /var/lib/snapd/apparmor/profiles that corresponds to your app
reload the profile with:
$ sudo apparmor_parser -r /var/lib/snapd/apparmor/profiles/<profile>
A seccomp denial will look something like:
audit: type=1326 audit(1430766107.122:16): auid=1000 uid=1000 gid=1000 ses=15 pid=1491 comm="env" exe="/bin/bash" sig=31 arch=40000028 syscall=983045 compat=0 ip=0xb6fb0bd6 code=0x0
The syscall=983045 can be resolved with the scmp_sys_resolver command (you may also use the sc-logresolve command). Eg:
$ scmp_sys_resolver 983045 set_tls
In general, if there are no seccomp denials, it shouldn't be blocking the app, however do keep in mind that if the app is somehow trying to elevate its privileges (eg, via a setuid executable) the app may receive a Permission denied error with no denial (see PR_SET_NO_NEW_PRIVS discussion above). If there are seccomp denials, you can unblock yourself by modifying the seccomp file in /var/lib/snapd/seccomp/profiles, then launch your app like normal (the launcher will pick up the change on app invocation).
Do note that the local modification will not be preserved on package update. If you believe you have found a bug, please file a bug against: https://bugs.launchpad.net/ubuntu/+source/apparmor/+filebug
Helpful degugging commands
sudo sysctl -w kernel.printk_ratelimit=0 will disable kernel rate limitingof denials
snappy-debug.security scanlog: follow /var/log/syslog` and show AppArmor and seccompg denial
snappy-debug.security disable-rate-limiting: disable kernel rate limiting
snappy-debug.security reload [<name>.<origin>]: reloads apparmor security policy into the kernel
snappy-debug.security regenerate [<name>.<origin>]: regenerate apparmor security policy from snappy packaging
- This is often helpful when developing your app or policy for it:
In one terminal launch snappy-debug.security scanlog:
$ sudo snappy-debug.security scanlog
In another (if daemon):
$ sudo journalctl -k -u <service name>| grep audit
Then launch the app normally or launch manually under confinement with:
$ aa-exec -p <profile name> -- /apps/<pkgname>/<version>/...
SecurityTeam/Specifications/SnappyConfinement (last edited 2016-11-17 16:29:21 by jdstrand)