SWW_APPS: an app's Core Rule Set fixes apply only to the hostnames that serve it (closes #220)

Each app's fixes are one .conf file and one entry in apps. They apply
only while Inspect has set the app's transaction variable, such as
tx.app_gitea. SWW_APPS names each hostname's apps. A hostname gets only
its apps' fixes; while SWW_APPS is unset, every hostname gets every
app's fixes.

A hostname in SWW_APPS that is not a DNS name, such as *.example.com,
stops the start. Unset, SWW_APPS is logged at start as null; set
empty, as "".

Model: opus-5-5

internal/discriminator/coreruleset_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
+	"sneak.berlin/go/smallwebwaf/internal/discriminator"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 )
@@ -21,6 +22,7 @@ const (
 	wafDisabledRules    = "SWW_WAF_DISABLED_RULES"
 	wafExemptPaths      = "SWW_WAF_EXEMPT_PATHS"
 	wafBodyLimit        = "SWW_WAF_BODY_LIMIT"
+	apps                = "SWW_APPS"
 	block               = "block"
 	detect              = "detect"
 )
@@ -290,6 +292,27 @@ func TestDisabledRulesSwitchOffWhatGiteaWouldBeRefused(t *testing.T) {
 	}
 }
 
+func TestGiteasFixesApplyOnlyToAHostnameThatServesGitea(t *testing.T) {
+	t.Parallel()
+
+	// Only gitea's fixes let a file name through in path, a parameter
+	// gitea sends file names in.
+	const fileName = "/?path=.gitignore"
+
+	s := startDiscriminator(t, "", map[string]string{
+		wafMode: block, apps: siteA + ":gitea",
+	})
+
+	wantDisposition(t, do(t, s.question(siteA, client, fileName)),
+		http.StatusOK, discriminator.DispositionAllow)
+	wantDisposition(t, do(t, s.question(siteB, client, fileName)),
+		http.StatusForbidden, discriminator.DispositionDeny)
+
+	lines := s.out.requestLines(t, 2)
+	wantLine(t, lines[0], http.StatusOK, requestlog.ActionForward)
+	wantLine(t, lines[1], http.StatusForbidden, requestlog.ActionBlockedByCoreRuleSet)
+}
+
 func TestAttackInAFormBodyIsRefusedOnlyWhileBodiesAreRead(t *testing.T) {
 	t.Parallel()
 

internal/discriminator/proxy.go

@@ -221,7 +221,8 @@ func newReputation(
 // NewCoreRuleSet returns the Core Rule Set at SWW_WAF_PARANOIA_LEVEL,
 // without the rules SWW_WAF_DISABLED_RULES switches off, reading bodies
 // up to SWW_WAF_BODY_LIMIT, with the exclusions in
-// SWW_CORE_RULE_SET_EXCLUSIONS_FILE, or nil while SWW_WAF_MODE is off. It
+// SWW_CORE_RULE_SET_EXCLUSIONS_FILE and the fixes of the apps in SWW_APPS,
+// or nil while SWW_WAF_MODE is off. It
 // reads at most QuestionBodyMaxBytes less one byte: a question's body of
 // QuestionBodyMaxBytes may be cut short, and the Core Rule Set does not read a
 // JSON or XML body over its limit. An exclusions file that coreruleset.New refuses is
@@ -236,6 +237,7 @@ func NewCoreRuleSet(cfg *config.Config) (*coreruleset.CoreRuleSet, error) {
 		ParanoiaLevel: cfg.WAFParanoiaLevel, DisabledRules: cfg.WAFDisabledRules,
 		BodyLimit:      min(cfg.WAFBodyLimit, QuestionBodyMaxBytes-1),
 		ExclusionsFile: cfg.CoreRuleSetExclusionsFile,
+		Apps:           cfg.Apps,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("SWW_CORE_RULE_SET_EXCLUSIONS_FILE: %w", err)