fix(routing): polish CIDR/regex/port-range matchers and document capset stance

CHANGES

@@ -1,6 +1,15 @@
 
 Changes with FreeUnit 1.35.4                                     xx xxx 2026
 
+    *) Bugfix: pass a non-zero ovector size to PCRE2 match-data create
+       (a 0 size is undefined per the PCRE2 docs) and reject malformed
+       port ranges of fewer than three bytes in HTTP routing.  Also
+       documents the symmetric pattern/request URI decoding, the
+       intentionally case-insensitive host matcher, and that the
+       Linux capability module does not call capset(2) — privilege
+       barriers in Unit are setuid + PR_SET_NO_NEW_PRIVS, not cap
+       drops.
+
     *) Bugfix: fix router process CPU spin and connection hang under port
        scanning load; CLOSE-WAIT sockets are now cleaned up properly on
        client FIN, idle connection queue iteration fixed, systemd file

src/nxt_capability.c

@@ -3,6 +3,18 @@
  * Copyright (C) NGINX, Inc.
  */
 
+/*
+ * NOTE: this module currently exposes capability *detection*
+ * (capget), used by nxt_isolation.c and the credential machinery to
+ * decide whether a non-root build can honor setuid/setgid in the
+ * "user"/"group" config keys.  Capabilities are NOT dropped
+ * programmatically via capset(2): the privilege barrier for app
+ * processes is the existing setuid + PR_SET_NO_NEW_PRIVS dance in
+ * nxt_credential.c / nxt_process.c.  Operators expecting an explicit
+ * capability-drop step should not assume one exists; isolation in
+ * Unit relies on uid/namespace/seccomp boundaries, not capset.
+ */
+
 #include <nxt_main.h>
 
 #if (NXT_HAVE_LINUX_CAPABILITY)

src/nxt_http_route.c

@@ -493,6 +493,13 @@ nxt_http_route_match_create(nxt_task_t *task, nxt_router_temp_conf_t *tmcf,
     }
 
     if (mtcf.host != NULL) {
+        /*
+         * Host matching is intentionally always case-insensitive
+         * (LOWCASE).  Per RFC 9110 §4.2.3 the host component is
+         * case-insensitive, and there is no per-rule sensitivity
+         * flag — an admin expecting case-sensitive host filtering
+         * will not get it from this rule.
+         */
         rule = nxt_http_route_rule_create(task, mp, mtcf.host, 1,
                                           NXT_HTTP_ROUTE_PATTERN_LOWCASE,
                                           NXT_HTTP_URI_ENCODING_NONE);
@@ -1176,6 +1183,15 @@ nxt_http_route_pattern_create(nxt_task_t *task, nxt_mp_t *mp,
 }
 
 
+/*
+ * Configured pattern strings are decoded once here at compile time,
+ * while request URIs are decoded by the HTTP parser before they reach
+ * the matcher.  Both paths funnel through the same nxt_decode_uri /
+ * nxt_decode_uri_plus helpers; %XX semantics are symmetric, so a
+ * "%2e%2e" in the configured pattern will compare against the same
+ * bytes a request "%2e%2e" decoded into.  If either helper's behaviour
+ * changes, route patterns and request URIs MUST be updated in lock-step.
+ */
 static nxt_int_t
 nxt_http_route_decode_str(nxt_str_t *str, nxt_http_uri_encoding_t encoding)
 {
@@ -2147,7 +2163,15 @@ nxt_http_route_pattern(nxt_http_request_t *r, nxt_http_route_pattern_t *pattern,
 #if (NXT_HAVE_REGEX)
     if (pattern->regex) {
         if (r->regex_match == NULL) {
-            r->regex_match = nxt_regex_match_create(r->mem_pool, 0);
+            /*
+             * Reuse one match-data struct across every pattern compiled
+             * against this request, so size it for the minimum ovector
+             * (one offset pair — the overall match).  Captures are not
+             * consulted by the matcher.  Passing 0 to PCRE2's
+             * pcre2_match_data_create() is undefined per the public
+             * docs; 1 is the documented minimum.
+             */
+            r->regex_match = nxt_regex_match_create(r->mem_pool, 1);
             if (nxt_slow_path(r->regex_match == NULL)) {
                 return NXT_ERROR;
             }

src/nxt_http_route_addr.c

@@ -261,6 +261,13 @@ nxt_http_route_addr_pattern_parse(nxt_mp_t *mp,
 
             goto parse_port;
         }
+
+        /*
+         * /32 is the single-host case; set EXACT explicitly so the
+         * state machine reflects intent rather than relying on the
+         * implicit assignment in the fallthrough path below.
+         */
+        base->match_type = NXT_HTTP_ROUTE_ADDR_EXACT;
     }
 
     inet->start = nxt_inet_addr(addr.start, addr.length);
@@ -283,7 +290,13 @@ nxt_http_route_addr_pattern_parse(nxt_mp_t *mp,
         return NXT_OK;
     }
 
-    delim = memchr(port.start, '-', port.length - 1);
+    /*
+     * Search the entire port string for '-' (the original "-1" bound
+     * silently ignored a trailing dash in inputs like "8-").  If the
+     * dash is at either end the resulting empty half makes
+     * nxt_int_parse() return < 0 below, producing PATTERN_PORT_ERROR.
+     */
+    delim = memchr(port.start, '-', port.length);
     if (delim != NULL) {
         ret = nxt_int_parse(port.start, delim - port.start);
         if (nxt_slow_path(ret < 0 || ret > 65535)) {