SECURITY: Fix is_private_ip for RateLimiter to cover all cases (#12464)

The regular expression to detect private IP addresses did not always detect them successfully.
Changed to use ruby's in-built IPAddr.new(ip_address).private? method instead
which does the same thing but covers all cases.

lib/middleware/request_tracker.rb

@@ -215,11 +215,9 @@ class Middleware::RequestTracker
     log_request_info(env, result, info) unless !log_request || env["discourse.request_tracker.skip"]
   end
 
-  PRIVATE_IP ||= /^(127\.)|(192\.168\.)|(10\.)|(172\.1[6-9]\.)|(172\.2[0-9]\.)|(172\.3[0-1]\.)|(::1$)|([fF][cCdD])/
-
   def is_private_ip?(ip)
     ip = IPAddr.new(ip) rescue nil
-    !!(ip && ip.to_s.match?(PRIVATE_IP))
+    !!(ip && (ip.private? || ip.loopback?))
   end
 
   def rate_limit(request)

spec/components/middleware/request_tracker_spec.rb

@@ -185,13 +185,18 @@ describe Middleware::RequestTracker do
       global_setting :max_reqs_per_ip_mode, 'warn+block'
       global_setting :max_reqs_rate_limit_on_private, true
 
-      env1 = env("REMOTE_ADDR" => "127.0.0.2")
+      addresses = %w[127.1.2.3 127.0.0.2 192.168.1.2 10.0.1.2 172.16.9.8 172.19.1.2 172.20.9.8 172.29.1.2 172.30.9.8 172.31.1.2]
+      warn_count = 1
+      addresses.each do |addr|
+        env1 = env("REMOTE_ADDR" => addr)
 
-      status, _ = middleware.call(env1)
-      status, _ = middleware.call(env1)
+        status, _ = middleware.call(env1)
+        status, _ = middleware.call(env1)
 
-      expect(Rails.logger.warnings).to eq(1)
-      expect(status).to eq(429)
+        expect(Rails.logger.warnings).to eq(warn_count)
+        expect(status).to eq(429)
+        warn_count += 1
+      end
     end
 
     describe "register_ip_skipper" do
@@ -227,13 +232,16 @@ describe Middleware::RequestTracker do
       global_setting :max_reqs_per_ip_mode, 'warn+block'
       global_setting :max_reqs_rate_limit_on_private, false
 
-      env1 = env("REMOTE_ADDR" => "127.0.3.1")
+      addresses = %w[127.1.2.3 127.0.3.1 192.168.1.2 10.0.1.2 172.16.9.8 172.19.1.2 172.20.9.8 172.29.1.2 172.30.9.8 172.31.1.2]
+      addresses.each do |addr|
+        env1 = env("REMOTE_ADDR" => addr)
 
-      status, _ = middleware.call(env1)
-      status, _ = middleware.call(env1)
+        status, _ = middleware.call(env1)
+        status, _ = middleware.call(env1)
 
-      expect(Rails.logger.warnings).to eq(0)
-      expect(status).to eq(200)
+        expect(Rails.logger.warnings).to eq(0)
+        expect(status).to eq(200)
+      end
     end
 
     it "does warn if rate limiter is enabled via warn+block" do