bugfix: heap-use-after-free in tcp_finalize after receiveuntil iterator GC.

finalize_read_part() only cleared cp->upstream and left
u->input_filter_ctx pointing to the compiled pattern, which the Lua GC
could free before the socket was finalized. Clear both sides.

See #2517.

Author: u5surf

src/ngx_http_lua_socket_tcp.c

@@ -4211,10 +4211,15 @@ ngx_http_lua_socket_tcp_finalize_read_part(ngx_http_request_t *r,
         ngx_memzero(&u->buffer, sizeof(ngx_buf_t));
     }
 
-    /* mirror tcp_finalize: detach cp so its __gc is safe */
+    /*
+     * mirror tcp_finalize: detach cp so its __gc is safe, and drop our
+     * reference to cp as well, since cp may be freed by the Lua GC before
+     * the socket is finalized.
+     */
     if (u->input_filter_ctx != NULL && u->input_filter_ctx != u) {
         ((ngx_http_lua_socket_compiled_pattern_t *)
          u->input_filter_ctx)->upstream = NULL;
+        u->input_filter_ctx = NULL;
     }
 
     if (u->raw_downstream || u->body_downstream) {

t/066-socket-receiveuntil.t

@@ -2012,3 +2012,74 @@ close: 1 nil
 --- no_error_log
 [error]
 --- skip_eval: 3:$ENV{TEST_NGINX_USE_HTTP3}
+
+
+
+=== TEST 27: close the socket after the iterator got a read error and was GC'ed (GH #2517)
+--- config
+    server_tokens off;
+    location /t {
+        content_by_lua_block {
+            -- JIT traces may keep the iterator closure alive
+            jit.off()
+            jit.flush()
+
+            local sock = ngx.socket.tcp()
+            local port = ngx.var.server_port
+
+            local ok, err = sock:connect("127.0.0.1", port)
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            local req = "GET /foo HTTP/1.0\r\nHost: localhost\r\nConnection: close\r\n\r\n"
+
+            local bytes, err = sock:send(req)
+            if not bytes then
+                ngx.say("failed to send request: ", err)
+                return
+            end
+
+            local weak = setmetatable({}, { __mode = "v" })
+
+            local function read_until_error()
+                local reader = sock:receiveuntil("--no-such-boundary")
+                weak[1] = reader
+
+                while true do
+                    local data, err = reader(1)
+                    if not data then
+                        ngx.say("failed to read: ", err)
+                        return
+                    end
+                end
+            end
+
+            read_until_error()
+
+            for _ = 1, 4 do
+                collectgarbage("collect")
+            end
+
+            ngx.say("reader collected: ", weak[1] == nil)
+
+            ok, err = sock:close()
+            ngx.say("close: ", ok, " ", err)
+        }
+    }
+
+    location /foo {
+        content_by_lua_block {
+            ngx.print("hello world")
+        }
+    }
+--- request
+GET /t
+--- response_body
+failed to read: closed
+reader collected: true
+close: 1 nil
+--- no_error_log
+[error]
+--- skip_eval: 3:$ENV{TEST_NGINX_USE_HTTP3}