Improve error reporting and logging when processing remote accounts (#15605)

* Add a more descriptive PrivateNetworkAddressError exception class

* Remove unnecessary exception class to rescue clause

* Remove unnecessary include to JsonLdHelper

* Give more neutral error message when too many webfinger redirects

* Remove unnecessary guard condition

* Rework how “ActivityPub::FetchRemoteAccountService” handles errors

Add “suppress_errors” keyword argument to avoid raising errors in
ActivityPub::FetchRemoteAccountService#call (default/previous behavior).

* Rework how “ActivityPub::FetchRemoteKeyService” handles errors

Add “suppress_errors” keyword argument to avoid raising errors in
ActivityPub::FetchRemoteKeyService#call (default/previous behavior).

* Fix Webfinger::RedirectError not being a subclass of Webfinger::Error

* Add suppress_errors option to ResolveAccountService

Defaults to true (to preserve previous behavior). If set to false,
errors will be raised instead of caught, allowing the caller to be
informed of what went wrong.

* Return more precise error when failing to fetch account signing AP payloads

* Add tests

* Fixes

* Refactor error handling a bit

* Fix various issues

* Add specific error when provided Digest is not 256 bits of base64-encoded data

* Please CodeClimate

* Improve webfinger error reporting

10 files changed, 158 insertions, 47 deletions

diff --git a/app/controllers/concerns/signature_verification.rb b/app/controllers/concerns/signature_verification.rb
index 4dd0cac55..89dc828f4 100644
--- a/app/controllers/concerns/signature_verification.rb
+++ b/app/controllers/concerns/signature_verification.rb
@@ -93,11 +93,15 @@ module SignatureVerification
 
     return account unless verify_signature(account, signature, compare_signed_string).nil?
 
-    @signature_verification_failure_reason = "Verification failed for #{account.username}@#{account.domain} #{account.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
-    @signed_request_account = nil
+    fail_with! "Verification failed for #{account.username}@#{account.domain} #{account.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
   rescue SignatureVerificationError => e
-    @signature_verification_failure_reason = e.message
-    @signed_request_account = nil
+    fail_with! e.message
+  rescue HTTP::Error, OpenSSL::SSL::SSLError => e
+    fail_with! "Failed to fetch remote data: #{e.message}"
+  rescue Mastodon::UnexptectedResponseError
+    fail_with! 'Failed to fetch remote data (got unexpected reply from server)'
+  rescue Stoplight::Error::RedLight
+    fail_with! 'Fetching attempt skipped because of recent connection failure'
   end
 
   def request_body
@@ -106,6 +110,11 @@ module SignatureVerification
 
   private
 
+  def fail_with!(message)
+    @signature_verification_failure_reason = message
+    @signed_request_account = nil
+  end
+
   def signature_params
     @signature_params ||= begin
       raw_signature = request.headers['Signature']
@@ -138,7 +147,17 @@ module SignatureVerification
     digests = request.headers['Digest'].split(',').map { |digest| digest.split('=', 2) }.map { |key, value| [key.downcase, value] }
     sha256  = digests.assoc('sha-256')
     raise SignatureVerificationError, "Mastodon only supports SHA-256 in Digest header. Offered algorithms: #{digests.map(&:first).join(', ')}" if sha256.nil?
-    raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}" if body_digest != sha256[1]
+
+    return if body_digest == sha256[1]
+
+    digest_size = begin
+      Base64.strict_decode64(sha256[1].strip).length
+    rescue ArgumentError
+      raise SignatureVerificationError, "Invalid Digest value. The provided Digest value is not a valid base64 string. Given digest: #{sha256[1]}"
+    end
+
+    raise SignatureVerificationError, "Invalid Digest value. The provided Digest value is not a SHA-256 digest. Given digest: #{sha256[1]}" if digest_size != 32
+    raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}"
   end
 
   def verify_signature(account, signature, compare_signed_string)
@@ -216,19 +235,20 @@ module SignatureVerification
     end
 
     if key_id.start_with?('acct:')
-      stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, '')) }
+      stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, ''), suppress_errors: false) }
     elsif !ActivityPub::TagManager.instance.local_uri?(key_id)
       account   = ActivityPub::TagManager.instance.uri_to_resource(key_id, Account)
-      account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false) }
+      account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false, suppress_errors: false) }
       account
     end
-  rescue Mastodon::HostValidationError
-    nil
+  rescue Mastodon::PrivateNetworkAddressError => e
+    raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})"
+  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteAccountService::Error, ActivityPub::FetchRemoteKeyService::Error, Webfinger::Error => e
+    raise SignatureVerificationError, e.message
   end
 
   def stoplight_wrap_request(&block)
     Stoplight("source:#{request.remote_ip}", &block)
-      .with_fallback { nil }
       .with_threshold(1)
       .with_cool_off_time(5.minutes.seconds)
       .with_error_handler { |error, handle| error.is_a?(HTTP::Error) || error.is_a?(OpenSSL::SSL::SSLError) ? handle.call(error) : raise(error) }
@@ -237,6 +257,10 @@ module SignatureVerification
 
   def account_refresh_key(account)
     return if account.local? || !account.activitypub?
-    ActivityPub::FetchRemoteAccountService.new.call(account.uri, only_key: true)
+    ActivityPub::FetchRemoteAccountService.new.call(account.uri, only_key: true, suppress_errors: false)
+  rescue Mastodon::PrivateNetworkAddressError => e
+    raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})"
+  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteAccountService::Error, Webfinger::Error => e
+    raise SignatureVerificationError, e.message
   end
 end
diff --git a/app/lib/request.rb b/app/lib/request.rb
index f5123d776..eac04c798 100644
--- a/app/lib/request.rb
+++ b/app/lib/request.rb
@@ -208,7 +208,7 @@ class Request
 
         addresses.each do |address|
           begin
-            check_private_address(address)
+            check_private_address(address, host)
 
             sock     = ::Socket.new(address.is_a?(Resolv::IPv6) ? ::Socket::AF_INET6 : ::Socket::AF_INET, ::Socket::SOCK_STREAM, 0)
             sockaddr = ::Socket.pack_sockaddr_in(port, address.to_s)
@@ -264,10 +264,10 @@ class Request
 
       alias new open
 
-      def check_private_address(address)
+      def check_private_address(address, host)
         addr = IPAddr.new(address.to_s)
         return if private_address_exceptions.any? { |range| range.include?(addr) }
-        raise Mastodon::HostValidationError if PrivateAddressCheck.private_address?(addr)
+        raise Mastodon::PrivateNetworkAddressError, host if PrivateAddressCheck.private_address?(addr)
       end
 
       def private_address_exceptions
diff --git a/app/lib/webfinger.rb b/app/lib/webfinger.rb
index a681e0815..7c0c10c33 100644
--- a/app/lib/webfinger.rb
+++ b/app/lib/webfinger.rb
@@ -3,7 +3,7 @@
 class Webfinger
   class Error < StandardError; end
   class GoneError < Error; end
-  class RedirectError < StandardError; end
+  class RedirectError < Error; end
 
   class Response
     attr_reader :uri
diff --git a/app/services/activitypub/fetch_remote_account_service.rb b/app/services/activitypub/fetch_remote_account_service.rb
index 9d01f5386..d7d739c59 100644
--- a/app/services/activitypub/fetch_remote_account_service.rb
+++ b/app/services/activitypub/fetch_remote_account_service.rb
@@ -5,10 +5,12 @@ class ActivityPub::FetchRemoteAccountService < BaseService
   include DomainControlHelper
   include WebfingerHelper
 
+  class Error < StandardError; end
+
   SUPPORTED_TYPES = %w(Application Group Organization Person Service).freeze
 
   # Does a WebFinger roundtrip on each call, unless `only_key` is true
-  def call(uri, id: true, prefetched_body: nil, break_on_redirect: false, only_key: false)
+  def call(uri, id: true, prefetched_body: nil, break_on_redirect: false, only_key: false, suppress_errors: true)
     return if domain_not_allowed?(uri)
     return ActivityPub::TagManager.instance.uri_to_resource(uri, Account) if ActivityPub::TagManager.instance.local_uri?(uri)
 
@@ -18,38 +20,50 @@ class ActivityPub::FetchRemoteAccountService < BaseService
       else
         body_to_json(prefetched_body, compare_id: id ? uri : nil)
       end
+    rescue Oj::ParseError
+      raise Error, "Error parsing JSON-LD document #{uri}"
     end
 
-    return if !supported_context? || !expected_type? || (break_on_redirect && @json['movedTo'].present?)
+    raise Error, "Error fetching actor JSON at #{uri}" if @json.nil?
+    raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?
+    raise Error, "Unexpected object type for actor #{uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_type?
+    raise Error, "Actor #{uri} has moved to #{@json['movedTo']}" if break_on_redirect && @json['movedTo'].present?
 
     @uri      = @json['id']
     @username = @json['preferredUsername']
     @domain   = Addressable::URI.parse(@uri).normalized_host
 
-    return unless only_key || verified_webfinger?
+    check_webfinger! unless only_key
 
     ActivityPub::ProcessAccountService.new.call(@username, @domain, @json, only_key: only_key, verified_webfinger: !only_key)
-  rescue Oj::ParseError
-    nil
+  rescue Error => e
+    Rails.logger.debug "Fetching account #{uri} failed: #{e.message}"
+    raise unless suppress_errors
   end
 
   private
 
-  def verified_webfinger?
+  def check_webfinger!
     webfinger                            = webfinger!("acct:#{@username}@#{@domain}")
     confirmed_username, confirmed_domain = split_acct(webfinger.subject)
 
-    return webfinger.link('self', 'href') == @uri if @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
+    if @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
+      raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+      return
+    end
 
     webfinger                            = webfinger!("acct:#{confirmed_username}@#{confirmed_domain}")
     @username, @domain                   = split_acct(webfinger.subject)
 
-    return false unless @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
-    return false if webfinger.link('self', 'href') != @uri
+    unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
+      raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{uri} (stopped at #{@username}@#{@domain})"
+    end
 
-    true
-  rescue Webfinger::Error
-    false
+    raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+  rescue Webfinger::RedirectError => e
+    raise Error, e.message
+  rescue Webfinger::Error => e
+    raise Error, "Webfinger error when resolving #{@username}@#{@domain}: #{e.message}"
   end
 
   def split_acct(acct)
diff --git a/app/services/activitypub/fetch_remote_key_service.rb b/app/services/activitypub/fetch_remote_key_service.rb
index c48288b3b..01008d883 100644
--- a/app/services/activitypub/fetch_remote_key_service.rb
+++ b/app/services/activitypub/fetch_remote_key_service.rb
@@ -3,9 +3,11 @@
 class ActivityPub::FetchRemoteKeyService < BaseService
   include JsonLdHelper
 
+  class Error < StandardError; end
+
   # Returns account that owns the key
-  def call(uri, id: true, prefetched_body: nil)
-    return if uri.blank?
+  def call(uri, id: true, prefetched_body: nil, suppress_errors: true)
+    raise Error, 'No key URI given' if uri.blank?
 
     if prefetched_body.nil?
       if id
@@ -13,7 +15,7 @@ class ActivityPub::FetchRemoteKeyService < BaseService
         if person?
           @json = fetch_resource(@json['id'], true)
         elsif uri != @json['id']
-          return
+          raise Error, "Fetched URI #{uri} has wrong id #{@json['id']}"
         end
       else
         @json = fetch_resource(uri, id)
@@ -22,21 +24,29 @@ class ActivityPub::FetchRemoteKeyService < BaseService
       @json = body_to_json(prefetched_body, compare_id: id ? uri : nil)
     end
 
-    return unless supported_context?(@json) && expected_type?
-    return find_account(@json['id'], @json) if person?
+    raise Error, "Unable to fetch key JSON at #{uri}" if @json.nil?
+    raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?(@json)
+    raise Error, "Unexpected object type for key #{uri}" unless expected_type?
+    return find_account(@json['id'], @json, suppress_errors) if person?
 
     @owner = fetch_resource(owner_uri, true)
 
-    return unless supported_context?(@owner) && confirmed_owner?
+    raise Error, "Unable to fetch actor JSON #{owner_uri}" if @owner.nil?
+    raise Error, "Unsupported JSON-LD context for document #{owner_uri}" unless supported_context?(@owner)
+    raise Error, "Unexpected object type for actor #{owner_uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_owner_type?
+    raise Error, "publicKey id for #{owner_uri} does not correspond to #{@json['id']}" unless confirmed_owner?
 
-    find_account(owner_uri, @owner)
+    find_account(owner_uri, @owner, suppress_errors)
+  rescue Error => e
+    Rails.logger.debug "Fetching key #{uri} failed: #{e.message}"
+    raise unless suppress_errors
   end
 
   private
 
-  def find_account(uri, prefetched_body)
+  def find_account(uri, prefetched_body, suppress_errors)
     account   = ActivityPub::TagManager.instance.uri_to_resource(uri, Account)
-    account ||= ActivityPub::FetchRemoteAccountService.new.call(uri, prefetched_body: prefetched_body)
+    account ||= ActivityPub::FetchRemoteAccountService.new.call(uri, prefetched_body: prefetched_body, suppress_errors: suppress_errors)
     account
   end
 
@@ -56,7 +66,11 @@ class ActivityPub::FetchRemoteKeyService < BaseService
     @owner_uri ||= value_or_id(@json['owner'])
   end
 
+  def expected_owner_type?
+    equals_or_includes_any?(@owner['type'], ActivityPub::FetchRemoteAccountService::SUPPORTED_TYPES)
+  end
+
   def confirmed_owner?
-    equals_or_includes_any?(@owner['type'], ActivityPub::FetchRemoteAccountService::SUPPORTED_TYPES) && value_or_id(@owner['publicKey']) == @json['id']
+    value_or_id(@owner['publicKey']) == @json['id']
   end
 end
diff --git a/app/services/activitypub/process_account_service.rb b/app/services/activitypub/process_account_service.rb
index 34750dba6..456b3524b 100644
--- a/app/services/activitypub/process_account_service.rb
+++ b/app/services/activitypub/process_account_service.rb
@@ -32,8 +32,6 @@ class ActivityPub::ProcessAccountService < BaseService
       process_duplicate_accounts! if @options[:verified_webfinger]
     end
 
-    return if @account.nil?
-
     after_protocol_change! if protocol_changed?
     after_key_change! if key_changed? && !@options[:signed_with_known_key]
     clear_tombstones! if key_changed?
diff --git a/app/services/resolve_account_service.rb b/app/services/resolve_account_service.rb
index b55e45409..e3b370968 100644
--- a/app/services/resolve_account_service.rb
+++ b/app/services/resolve_account_service.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 class ResolveAccountService < BaseService
-  include JsonLdHelper
   include DomainControlHelper
   include WebfingerHelper
   include Redisable
@@ -13,6 +12,7 @@ class ResolveAccountService < BaseService
   # @param [Hash] options
   # @option options [Boolean] :redirected Do not follow further Webfinger redirects
   # @option options [Boolean] :skip_webfinger Do not attempt any webfinger query or refreshing account data
+  # @option options [Boolean] :suppress_errors When failing, return nil instead of raising an error
   # @return [Account]
   def call(uri, options = {})
     return if uri.blank?
@@ -52,15 +52,15 @@ class ResolveAccountService < BaseService
     # either needs to be created, or updated from fresh data
 
     fetch_account!
-  rescue Webfinger::Error, Oj::ParseError => e
+  rescue Webfinger::Error => e
     Rails.logger.debug "Webfinger query for #{@uri} failed: #{e}"
-    nil
+    raise unless @options[:suppress_errors]
   end
 
   private
 
   def process_options!(uri, options)
-    @options = options
+    @options = { suppress_errors: true }.merge(options)
 
     if uri.is_a?(Account)
       @account  = uri
@@ -96,7 +96,7 @@ class ResolveAccountService < BaseService
     @username, @domain = split_acct(@webfinger.subject)
 
     unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
-      raise Webfinger::RedirectError, "The URI #{uri} tries to hijack #{@username}@#{@domain}"
+      raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{uri} (stopped at #{@username}@#{@domain})"
     end
   rescue Webfinger::GoneError
     @gone = true
@@ -110,7 +110,7 @@ class ResolveAccountService < BaseService
     return unless activitypub_ready?
 
     with_lock("resolve:#{@username}@#{@domain}") do
-      @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url)
+      @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url, suppress_errors: @options[:suppress_errors])
     end
 
     @account
diff --git a/lib/exceptions.rb b/lib/exceptions.rb
index 0c677b660..3c5ba226b 100644
--- a/lib/exceptions.rb
+++ b/lib/exceptions.rb
@@ -25,4 +25,13 @@ module Mastodon
       end
     end
   end
+
+  class PrivateNetworkAddressError < HostValidationError
+    attr_reader :host
+
+    def initialize(host)
+      @host = host
+      super()
+    end
+  end
 end
diff --git a/spec/services/activitypub/fetch_remote_account_service_spec.rb b/spec/services/activitypub/fetch_remote_account_service_spec.rb
index aa13f0a9b..ec6f1f41d 100644
--- a/spec/services/activitypub/fetch_remote_account_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_account_service_spec.rb
@@ -119,6 +119,58 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       include_examples 'sets profile data'
     end
 
+    context 'when WebFinger returns a different URI' do
+      let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
+
+      before do
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+      end
+
+      it 'fetches resource' do
+        account
+        expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+      end
+
+      it 'looks up webfinger' do
+        account
+        expect(a_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com')).to have_been_made.once
+      end
+
+      it 'does not create account' do
+        expect(account).to be_nil
+      end
+    end
+
+    context 'when WebFinger returns a different URI after a redirection' do
+      let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
+
+      before do
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+        stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
+      end
+
+      it 'fetches resource' do
+        account
+        expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+      end
+
+      it 'looks up webfinger' do
+        account
+        expect(a_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com')).to have_been_made.once
+      end
+
+      it 'looks up "redirected" webfinger' do
+        account
+        expect(a_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af')).to have_been_made.once
+      end
+
+      it 'does not create account' do
+        expect(account).to be_nil
+      end
+    end
+
     context 'with wrong id' do
       it 'does not create account' do
         expect(subject.call('https://fake.address/@foo', prefetched_body: Oj.dump(actor))).to be_nil
diff --git a/spec/services/resolve_account_service_spec.rb b/spec/services/resolve_account_service_spec.rb
index 8c302e1d8..654606bea 100644
--- a/spec/services/resolve_account_service_spec.rb
+++ b/spec/services/resolve_account_service_spec.rb
@@ -137,8 +137,8 @@ RSpec.describe ResolveAccountService, type: :service do
       stub_request(:get, 'https://evil.example.com/.well-known/webfinger?resource=acct:foo@evil.example.com').to_return(body: Oj.dump(webfinger2), headers: { 'Content-Type': 'application/jrd+json' })
     end
 
-    it 'returns new remote account' do
-      expect { subject.call('Foo@redirected.example.com') }.to raise_error Webfinger::RedirectError
+    it 'does not return a new remote account' do
+      expect(subject.call('Foo@redirected.example.com')).to be_nil
     end
   end