FIX: Gracefully handle DNS issued from SSRF lookup when inline oneboxing (#19631)

There is an issue where chat message processing breaks due to
unhandles `SocketError` exceptions originating in the SSRF check,
specifically in `FinalDestination::Resolver`.

This change gives `FinalDestination::SSRFDetector` a new error class
to wrap the `SocketError` in, and haves the `RetrieveTitle` class
handle that error gracefully.

lib/final_destination/ssrf_detector.rb

@@ -2,8 +2,8 @@
 
 class FinalDestination
   module SSRFDetector
-    class DisallowedIpError < SocketError
-    end
+    class DisallowedIpError < SocketError; end
+    class LookupFailedError < SocketError; end
 
     def self.standard_private_ranges
       @private_ranges ||= [
@@ -61,7 +61,12 @@ class FinalDestination
     end
 
     def self.lookup_and_filter_ips(name, timeout: nil)
-      ips = lookup_ips(name, timeout: timeout)
+      begin
+        ips = lookup_ips(name, timeout: timeout)
+      rescue SocketError
+        raise LookupFailedError, "FinalDestination: lookup failed"
+      end
+
       return ips if host_bypasses_checks?(name)
 
       ips.filter! { |ip| FinalDestination::SSRFDetector.ip_allowed?(ip) }

lib/retrieve_title.rb

@@ -9,7 +9,7 @@ module RetrieveTitle
       max_redirects: max_redirects,
       initial_https_redirect_ignore_limit: initial_https_redirect_ignore_limit
     )
-  rescue Net::ReadTimeout
+  rescue Net::ReadTimeout, FinalDestination::SSRFDetector::LookupFailedError
     # do nothing for Net::ReadTimeout errors
   end
 

spec/lib/final_destination/ssrf_detector_spec.rb

@@ -95,6 +95,13 @@ describe FinalDestination::SSRFDetector do
       )
     end
 
+    it "raises an exception if lookup fails" do
+      subject.stubs(:lookup_ips).raises(SocketError)
+      expect { subject.lookup_and_filter_ips("example.com") }.to raise_error(
+        subject::LookupFailedError,
+      )
+    end
+
     it "bypasses filtering for allowlisted hosts" do
       SiteSetting.allowed_internal_hosts = "example.com"
       subject.stubs(:lookup_ips).returns(["127.0.0.1"])

spec/lib/retrieve_title_spec.rb

@@ -162,7 +162,13 @@ RSpec.describe RetrieveTitle do
     it "it ignores Net::ReadTimeout errors" do
       stub_request(:get, "https://example.com").to_raise(Net::ReadTimeout)
 
-      expect { RetrieveTitle.crawl("https://example.com") }.not_to raise_error
+      expect(RetrieveTitle.crawl("https://example.com")).to eq(nil)
+    end
+
+    it "ignores SSRF lookup errors" do
+      subject.stubs(:fetch_title).raises(FinalDestination::SSRFDetector::LookupFailedError)
+
+      expect(RetrieveTitle.crawl("https://example.com")).to eq(nil)
     end
   end