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JEP-227: Replace Acegi Security with Spring Security & upgrade Spring Framework

Abstract

The Acegi Security library, used as the basis for the Jenkins security system, is replaced with a current version of its successor, Spring Security. Additionally, the Spring Framework libraries required by Spring Security (and to a small extent independently by Jenkins) are updated to the current version. Some Acegi Security types remain in the Jenkins API, but reimplemented as façades to delegate to Spring Security, to offer a modicum of backward compatibility for the many plugins referring to these types. Key plugins interacting with the security system are made to work with the update, by patching the plugins where required.

Specification

This work consists of several aspects, both in Jenkins core and plugins.

  • The Acegi Security library is removed from the classpath of Jenkins core, replaced with the current release of Spring Security.

    • All of Spring is also updated to the current release (5.x).

    • LDAP-specific classes are not readded.

  • All of Jenkins core is switched to use Spring Security as its primary model.

  • BeanBuilder and associated classes, used to configure a security realm from a Groovy resource, are deleted, replaced by type-safe Java.

  • Plugin-facing APIs referring to Acegi Security are kept binary compatible wherever feasible.

    • Many org.acegisecurity.* types are reintroduced, but using clean reimplementations.

    • Most existing Jenkins API methods referring to org.acegisecurity.* types are retained, but deprecated and bridged to new Spring Security equivalents, typically ending in a 2 suffix.

    • toSpring and fromSpring methods are provided to interconvert Acegi Security and Spring Security types where applicable.

    • Subtyping is not used: the Acegi Security and Spring Security types are incomparable.

    • org.springframework.dao.DataAccessException and similar types are deprecated without replacement.

    • Sid and subtypes are for now simply reimplemented, rather than delegating to the spring-security-acl module.

  • Inessential uses of Acegi Security in plugins for which compatibility in Jenkins core would be awkward are replaced. (For example, exotic types in functional tests are replaced with simpler and more common APIs.)

  • Certain plugins with sophisticated implementations of SecurityRealm are patched.

    • All plugins using BeanBuilder are switched to using type-safe Java.

    • The ldap plugin has two patched versions:

      • One which bundles Acegi Security (including LDAP types) and does not use BeanBuilder, so that it can be run against either old or new cores.

      • A second derived from the first but which builds against new cores and Spring Security.

Rollout plan

In mostly chronological order, though of course many tasks can be parallelized:

  • Prepare the patch to core, verifying that it passes all tests and that basic scenarios without plugins work.

  • Run the tool to search for API usages in Jenkins plugins, checking all plugins in the update center for any usages of either Spring or Acegi Security types. Classify all matches in a document associated with this JEP.

  • Perform textual searches for certain deleted/missing APIs or problematic code idioms in the @jenkinsci organization, classifying all matches.

  • Prepare cleanup patches to plugins that would be acceptable even without this migration, and get them merged and released.

  • Prepare patches to plugins defining security realms, or any others which may require significant changes to be compatible.

    • ldap needs extensive work.

  • Run acceptance tests (ATH) and plugin compatibility tests (PCT) against core plus a representative subset of plugins.

  • Interactively verify that core plus all plugins mentioned in the setup wizard (even if not suggested) seem to work.

  • Evaluate the japicmp report for Jenkins core to make sure that all incompatible as well as compatible API changes are expected.

  • Solicit code reviews on all open associated pull requests to core and plugins.

  • Create a compatibility chart associated with this JEP listing all known plugins that might be affected by this change, with their current status.

  • Define a Jira label for regressions suspected to be related to this migration, for ease of tracking from the compatibility chart and the JEP.

  • Warn users of the upcoming changes, for example on the users’ mailing list, via blog post, social media, etc.

  • Release the version of ldap bundling Acegi Security. (This may be done well in advance of the core release, so that most users will have already upgraded.)

  • Release versions of other security realm plugins without BeanBuilder, such as active-directory.

  • Release core, including a warning in the release notes about the risk.

  • Release the version of ldap based on the new core release and using Spring Security.

  • For a reasonable period of time (months?), monitor Jira for reported regressions as well as the overall score given to Jenkins weekly releases.

  • Track the status of other “long-tail” plugins, offering advice and assistance to maintainers.

Motivation

False positives from scanners

Many security-conscious organizations using, or planning to use, Jenkins will run off-the-shelf security scanners to look for known vulnerabilities. These will commonly flag the extremely old Acegi Security and Spring Core libraries as susceptible and recommend upgrading. While the Jenkins CERT team does not believe that any of these issues are actually exploitable in Jenkins, it is time-consuming for the CERT team to respond to purported security reports, and for users to justify exemptions from policy to use Jenkins anyway.

Technical debt

A lot of this code was written 13 years ago by Kohsuke, has barely been touched since, and involves heavy modifications to Acegi Security functionality, in some cases apparently to work around limitations that may well have been addressed years ago in Spring Security. Working with long-obsolete APIs is tricky due to lack of knowledge—the Spring Security maintainer may barely remember how things were. The Jenkins CERT team has to examine code for vulnerabilities rather than relying on community knowledge in CVEs.

Reasoning

Status quo

Continuing to use Acegi Security indefinitely does not seem sustainable.

Repackaging Spring Security

It might seem to suffice to use something like the Maven Shade plugin to take a recent Spring Security release and move types to org.acegisecurity.* packages. That would ensure that Jenkins is using up-to-date implementation code, without requiring plugins to switch packages.

However this idea presumes that the changes from Acegi Security to Spring Security 2 consisted solely of package (and occasionally type) renames, and that Spring Security 3, 4, and 5 included only backward-compatible changes. These assumptions do not hold: while many pieces of client code would indeed compile and run after merely updating type names, there have been numerous changes which would break some clients:

  • deleted types (e.g. AcegiSecurityException has no replacement)

  • class refactorings (e.g., HttpSessionContextIntegrationFilter split into SecurityContextPersistenceFilter plus SecurityContextRepository and more)

  • methods renamed, parameters deleted, and parameter and return types changed (e.g., PasswordEncoder.encodePassword(String, Object)String encode(CharSequence))

Bytecode patching

A related notion is to include Spring Security verbatim in Jenkins core, and encourage plugins to compile against it directly, but offer binary (not source) compatibility for existing plugin releases by dynamically changing constant pool references in Java bytecode as it is loaded. Jenkins already uses a bytecode-compatibility-transformer library to process @AdaptField annotations for binary compatibility; this would be a more extensive transformation.

Besides the usual severe drawbacks of such tricks—opacity, lack of interoperation with debuggers and other IDE tooling, lack of source compatility—this approach suffers from the same problems as repackaging: it would only even work for the relatively simple package/class renames. (Trying to patch bytecode to accommodate deeper changes such as to method signatures would require a large, complex tool that does not yet exist.)

Delegating to Spring Security

A possibility considered early during development was to have Jenkins core security implementation classes and plugins continue to refer to Acegi Security types, but with the bodies of those types reimplemented to delegate to Spring Security equivalents. This seemed very confusing as we would continue to have two related APIs in the classpath and in active use indefinitely. It was also unclear how to make Jenkins implementation classes such as security filters work with such façades: these classes dive heavily into details of the Acegi/Spring Security APIs, so would need numerous Acegi Security types to delegate, even if no plugin ever cared.

Java overloads vs. 2 suffix

In certain cases, a Spring version of a method could have been defined as a Java overload. For example, AccessControlled.hasPermission(Authentication, Permission) could have had two overloads, one for org.acegisecurity.Authentication and one for org.springframework.security.core.Authentication.

However in many cases the method changed return type, which Java overloads do not support, meaning a new method name was required. The convention in Jenkins APIs is to append 2 to replacement interfaces or methods (or 3 after 2, etc.) so that was adopted here, and for consistency was used in all cases even where an overload could have been used.

Thus a plugin developer moving to a post-Spring Jenkins baseline has a straightforward rule for most of the changes: replace Acegi Security with Spring Security in import statements, and append 2 to method calls or overrides where required to satisfy the compiler. (There are a few other common changes which do not fit into this pattern, according to design changes in Spring Security, such as GrantedAuthority[] changing to Collection<? extends GrantedAuthority>.)

Making Acegi Security types extend Spring Security types

Early attempt to bridge Acegi Security types to Spring Security types involved using subtype relationships. For example, org.acegisecurity.Authentication would extend org.springframework.security.core.Authentication, so you could just use an implementation of the older interface wherever the newer interface was expected.

This quickly became difficult. Some methods could not be declared as overrides; in this example, the return type of getAuthorities changed from GrantedAuthority[] to Collection<? extends GrantedAuthority>. A more subtle problem involved covariance and contravariance in interface signatures referring to other interfaces in the API. Keeping the types distinct and offering methods to interconvert turned out to be easier to reason about.

Initially a special case was made for exception types. Since an exception can be thrown up through a call stack and caught by code anywhere, it is not possible to use interconversion methods in all cases. The key problem is hudson.security.AccessDeniedException2, thrown from failed ACL permission checks. A number of places not just in core but plugins catch its supertype org.acegisecurity.AccessDeniedException in order to recover gracefully from lack of permissions. Therefore, for compatibility, AccessDeniedException2 was initially made to implement both the Acegi Security and Spring Security versions of AccessDeniedException, and similarly for other exception types defined in Acegi Security. Unfortunately even this caused errors:

java.lang.VerifyError: Stack map does not match the one at exception handler 173
Exception Details:
  Location:
    org/jenkinsci/plugins/matrixauth/AuthorizationContainerDescriptor.doCheckName_(Ljava/lang/String;Lhudson/security/AccessControlled;Lhudson/security/Permission;)Lhudson/util/FormValidation; @173: astore
  Reason:
    Type 'org/acegisecurity/userdetails/UsernameNotFoundException' (current frame, stack[0]) is not assignable to 'org/springframework/core/NestedRuntimeException' (stack map, stack[0])

Providing binary compatibility for all plugins implementing SecurityRealm

Some plugins like sfee which implement SecurityRealm pose a special problem. When using complex features of Acegi Security, such as classes like ProviderManager which are difficult to provide compatible replacements for, these may simply require new releases built against a new Jenkins baseline and thus Spring Security. However it is unclear how users would get the new version of Jenkins and the new version of the plugin atomically (even assuming they read release notes in advance): the update center lets you download a plugin update to be installed after next start, which could be timed to coincide with a core update, but you could not download a plugin update declared to require a newer core version than you currently run. Worse, you cannot just upgrade Jenkins and immediately select the plugin update and restart again, since you would not be able to log in after the first restart if the security realm did not work!

Even assuming the timing issue is resolved, publishing new releases of all these plugins would be a significant effort. Fortunately there are not that many of them.

At least in the case of the ldap plugin, it suffices to bundle acegi-security-1.0.7.jar and spring-dao-1.2.9.jar, which are ignored in old versions of Jenkins, but actually used in new Jenkins as an overlay (using the core-defined stubs plus other types not overridden in core): the only interaction with Jenkins exported APIs involves methods with compatibility bridges. It is necessary to remove usages of BeanBuilder and switch to configuration in Java code.

Simple implementations of AbstractPasswordBasedSecurityRealm, such as in the pam-auth plugin, work without modifications. Some SSO plugins, such as github-oauth, also work without modifications.

Simplified interface to security

Many plugins do nothing complicated with Acegi Security types but are obliged to refer to this API to work with other parts of Jenkins. We may be able to introduce a new simplified API in jenkins.security.* to hide the details of Spring Security and cover the operations most commonly required by plugins:

  • obtain current identity, whether a real person ~ User or SYSTEM or ANONYMOUS or an unidentified but authenticated person

  • check password

  • temporarily switch identity

  • check permissions This would arguably increase ease of use of the API, and insulate most plugins from possible future incompatibilities in Spring Security. On the other hand, it would not suffice for plugins implementing SecurityRealm.

Hiding Spring Security from plugin classpath

Probably feasible for typical plugins, but unclear how this would work for plugins implementing SecurityRealm in general. For example, ldap makes use of the Acegi/Spring Security type LdapUserDetails, a subtype of UserDetails. Currently this is returned directly from API implementation methods. If Jenkins core required use of its own types, this would need to converted from Acegi/Spring Security. And that conversion could not be defined in Jenkins core for common use.

Hiding Spring Core from plugin classpath

JENKINS-49555 proposes this, to make it easier for plugins to bundle third-party libraries which use Spring Core. It is unclear if that would be possible if Spring Security, which depends on Spring Core, is reëxported from Jenkins core (i.e., not “hidden”)—do Spring Security types mention Spring Core types?

Backwards Compatibility

This JEP consists almost primarily of backwards compatibility concerns. See the compatibility table for current status.

It may be possible to use the detached plugin mechanism to offer upgrades of difficult plugins automatically. However the only detached plugins which implement security realms, ldap and pam-auth, can already run in either old or new Jenkins cores. At least the required update to the ldap plugin can be done via this mechanism.

The ability to override basic security component configuration in Jenkins via Groovy files, either in core via SecurityFilters.groovy or in a security realm plugin such as ldap via LDAPBindSecurityRealm.groovy, has been removed. Customizations to security-related settings now need to go through regular supported configuration (GUI or JCasC).

Searching for API usages in sources

There are some code idioms (in both main and test sources) which cannot or will not be made compatible and which just need to be adjusted:

Searching for API usages in binaries

Create /tmp/additionalClasses with initial content taken from review of the core PR, such as:

hudson/security/AccessDeniedException2
hudson/security/AccessDeniedHandlerImpl
hudson/security/AuthenticationManagerProxy
hudson/security/AuthenticationProcessingFilter2
hudson/security/ContainerAuthentication
hudson/security/DeferredCreationLdapAuthoritiesPopulator
hudson/security/HttpSessionContextIntegrationFilter2
hudson/security/HudsonAuthenticationEntryPoint
hudson/security/HudsonPrivateSecurityRealm$Details
hudson/security/InvalidatableUserDetails
hudson/security/NotSerilizableSecurityContext
hudson/security/RememberMeServicesProxy
hudson/security/TokenBasedRememberMeServices2
hudson/security/UserDetailsServiceProxy
hudson/security/UserMayOrMayNotExistException
hudson/util/spring/BeanBuilder
hudson/util/spring/BeanConfiguration
hudson/util/spring/ClosureScript
hudson/util/spring/DefaultBeanConfiguration
hudson/util/spring/DefaultRuntimeSpringConfiguration
hudson/util/spring/RuntimeSpringConfiguration
jenkins/security/ExceptionTranslationFilter
jenkins/security/NonSerializableSecurityContext
jenkins/security/UserDetailsCache

Add all Acegi Security and Spring types:

mvn -f jenkinsci/jenkins -pl core dependency:tree | \
  perl -n -e 'if (/([^ ]+):((spring|acegi).+):jar:(.+):compile/) {my $g = $1; $g =~ tr!.!/!; print("$ENV{HOME}/.m2/repository/$g/$2/$4/$2-$4.jar\n")}' | \
  xargs -n1 jar tf | fgrep .class | sed -e 's/.class$//' | sort | uniq >> /tmp/additionalClasses

Then use jenkins-infra/usage-in-plugins to look for usages in plugins, including those in CloudBees CI:

mvn process-classes exec:exec -Dexec.executable=java -Dexec.args='-classpath %classpath org.jenkinsci.deprecatedusage.Main --additionalClasses /space/tmp/additionalClasses --onlyIncludeSpecified --updateCenter https://jenkins-updates.cloudbees.com/update-center/envelope-core-oc/update-center.json?version=2.235.5.1,https://jenkins-updates.cloudbees.com/update-center/envelope-core-mm/update-center.json?version=2.235.5.1'

producing a long report.

(This pair of UCs is very nearly a superset of the default Jenkins UC.)

Alternately, the search can be focused on types which do not have a supposedly compatible replacement, by deleting these, such as:

hudson/security/AccessDeniedException2
hudson/security/UserMayOrMayNotExistException
org/acegisecurity/AccessDeniedException
org/acegisecurity/AcegiSecurityException
org/acegisecurity/acls/sid/GrantedAuthoritySid
org/acegisecurity/acls/sid/PrincipalSid
org/acegisecurity/acls/sid/Sid
org/acegisecurity/Authentication
org/acegisecurity/AuthenticationException
org/acegisecurity/AuthenticationManager
org/acegisecurity/AuthenticationServiceException
org/acegisecurity/BadCredentialsException
org/acegisecurity/context/SecurityContext
org/acegisecurity/context/SecurityContextHolder
org/acegisecurity/context/SecurityContextImpl
org/acegisecurity/GrantedAuthority
org/acegisecurity/GrantedAuthorityImpl
org/acegisecurity/providers/AbstractAuthenticationToken
org/acegisecurity/providers/anonymous/AnonymousAuthenticationToken
org/acegisecurity/providers/AuthenticationProvider
org/acegisecurity/providers/dao/AbstractUserDetailsAuthenticationProvider
org/acegisecurity/providers/UsernamePasswordAuthenticationToken
org/acegisecurity/ui/rememberme/RememberMeServices
org/acegisecurity/ui/WebAuthenticationDetails
org/acegisecurity/userdetails/User
org/acegisecurity/userdetails/UserDetails
org/acegisecurity/userdetails/UserDetailsService
org/acegisecurity/userdetails/UsernameNotFoundException
org/springframework/dao/DataAccessException
org/springframework/dao/DataAccessResourceFailureException
org/springframework/dao/DataRetrievalFailureException

producing a much shorter report. Some matches are from plugins which already have preparatory patches. A number of the remaining matches are Spring types that are probably compatible from 2.x to 5.x.

Security

This JEP changes Jenkins code fundamental to security and so introduces inherent security risks. There is no specific, expected risk.

Infrastructure Requirements

If binary compatibility cannot be offered for critical plugins, and the issue cannot be handled by code running inside Jenkins core itself, there may be a need to make changes to the Jenkins update center (JENKINS-49651). No such cases are currently expected.

Testing

There is an extensive need for testing associated with this change, due to the high risk of regression. It is unclear how extensive test coverage in Jenkins core really is when it comes to subtle aspects of the security system dating from 2007.

plugin-compat-tester is of use to detect plugin incompatibilities.

acceptance-test-harness is needed, especially with Dockerized fixtures, to run smoke tests of security-related workflows such as LDAP authentication.

CloudBees is running the ATH & PCT against patched Jenkins core and many popular plugins (“Tier 1” and “Tier 2”).

Prototype Implementation

References