README: what rproxy gives an app without waf (closes #386)

Adds a paragraph to "What it does" listing what rproxy enforces with
default settings whether or not waf answers: malformed requests, methods,
header size, request and response times, body sizes, idle connections.
After the list, it says which header limits are waf's.

Removes the "Slow and oversized requests" bullet, which the new list
states with figures.

Model: opus-5-5

README.md

@@ -2,7 +2,20 @@
 
 `smallwebwaf` is an MIT-licensed web application firewall, written in Go by
 [@sneak](https://sneak.berlin), for self-hosted web apps. It refuses the
-requests of scrapers, scanners and other abusers before they reach an app.
+requests of misbehaving scrapers, scanners and other abusers before they reach
+an app.
+
+With the default settings, a client is banned when it does any of these:
+
+- makes more than 120 requests in a minute, 1500 in an hour or 6000 in a day;
+- moves more than `50G` of request and response bodies in an hour, or `100G` in
+  a day;
+- asks for a secret or backup file, such as `/.env` or `/.git/config`;
+- sends a user agent that names a security scanner, such as `sqlmap` or `nikto`;
+- has more than 30 requests in a minute refused as probes or attacks.
+
+A scraper that does none of these is left alone. A scraper that waits 15 seconds
+between requests stays under the rate limits.
 
 ## What it does
 
@@ -10,10 +23,10 @@ A web application firewall reads each request on its way to a web app and
 refuses the ones that look like abuse. `smallwebwaf` is one program, `sww`,
 shipped in one image, with two commands that do this together:
 
-- `sww rproxy` is a small reverse proxy in front of one app. traefik routes to
-  it. It asks `waf` about each request, passes the allowed ones to the app, and
-  passes the app's answers back. It keeps nothing between requests and writes
-  nothing to disk.
+- `sww rproxy` is a small reverse proxy in front of one app. It sits behind a
+  TLS-terminating proxy, such as traefik, nginx or Caddy. It asks `waf` about
+  each request, passes the allowed ones to the app, and passes the app's answers
+  back. It keeps nothing between requests and writes nothing to disk.
 - `sww waf` decides. It runs the checks and keeps the bans, the counters and
   each client's history. One `waf` serves many sites: a client banned through
   one site is refused on all of them, and its requests on all of them count
@@ -74,8 +87,7 @@ For the operator, it:
 
 Not built, and not planned:
 
-- TLS and routing by host name. Both stay with traefik, the reverse proxy in
-  front of `rproxy`.
+- TLS and routing by host name. Both stay with the TLS-terminating proxy.
 - Browser challenges such as captchas.
 - A web console, or a configuration file.
 - Defence against floods large enough to fill the host's network link.
@@ -107,20 +119,61 @@ accepts connections, whether or not `waf` answers; in `waf`'s container, once
 The usual setup is three containers on one private network:
 
 - the app;
-- `rproxy`, in front of the app, which traefik routes to:
+- `rproxy`, in front of the app, which the TLS-terminating proxy forwards to:
   `SWW_RPROXY_WAF_BACKEND` names `waf` and `SWW_RPROXY_UPSTREAM_URL` names the
   app;
 - `waf`, with `SWW_COMMAND=waf` and a volume at `/var/lib/sww` for its state
   files.
 
-Point traefik's labels at port 8080 of `rproxy`
-(`traefik.http.services.<name>.loadbalancer.server.port=8080`). Publish no port
-of the app or of `waf`. Anything on that network can reach the app around
-`rproxy`, and can ask `waf` questions, so the network holds only what you trust.
-Each further app adds its own container and its own `rproxy`, whose
+Publish no port of the app or of `waf`. Anything on that network can reach the
+app around `rproxy`, and can ask `waf` questions, so the network holds only what
+you trust. Each further app adds its own container and its own `rproxy`, whose
 `SWW_RPROXY_WAF_BACKEND` names the same `waf`. The "Smallest setup" example
 below shows this shape.
 
+### The TLS-terminating proxy
+
+`rproxy` serves plain HTTP. It runs behind any TLS-terminating proxy, such as
+traefik, nginx or Caddy. The TLS-terminating proxy must:
+
+- forward each request to port 8080 of `rproxy` over plain HTTP;
+- keep the visitor's `Host` header;
+- add the visitor's address to `X-Forwarded-For`;
+- set `X-Forwarded-Proto` to the scheme the visitor used;
+- close an unused connection to `rproxy` in under 120 seconds;
+- connect to `rproxy` from an address in `SWW_RPROXY_TRUSTED_PROXIES`, by
+  default `10.0.0.0/8`, `172.16.0.0/12` or `192.168.0.0/16`.
+
+From any other address, `rproxy` ignores the forwarded headers and takes the
+TLS-terminating proxy for the visitor. Every visitor then shares one address,
+and one ban.
+
+traefik and Caddy keep the `Host` header and set both forwarded headers by
+default. traefik's Docker label
+`traefik.http.services.<name>.loadbalancer.server.port=8080` names the port.
+Caddy keeps an unused connection for 120 seconds by default, so its site
+shortens that to 90 seconds:
+
+```caddyfile
+reverse_proxy rproxy:8080 {
+    transport http {
+        keepalive 90s
+    }
+}
+```
+
+By default nginx sends the host in `proxy_pass` as `Host` and sets neither
+forwarded header, so its site sets all three:
+
+```nginx
+location / {
+    proxy_pass http://rproxy:8080;
+    proxy_set_header Host $host;
+    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+    proxy_set_header X-Forwarded-Proto $scheme;
+}
+```
+
 ### `rproxy` in the app's container
 
 An app's image can instead be built on the `smallwebwaf` image, so that `rproxy`
@@ -171,13 +224,13 @@ entrypoint starts `rproxy` and the app side by side, each as its own user. Run
 the app's image with `SWW_RPROXY_WAF_BACKEND` set. `deploy/example-app` is such
 an app, and the "`rproxy` beside the app" example below runs one.
 
-The app sees the headers traefik sent, with traefik's address added to
-`X-Forwarded-For`, from a TCP peer that is `rproxy`. So the app must trust
-`rproxy`'s address for forwarded headers. In a container of its own, `rproxy` is
-on the private network, which the usual default of a trusted-proxy setting
-covers. Beside the app, its address is `127.0.0.1` or `::1`, which the private
-ranges leave out, so the app's own setting must name them too, as `app.run`
-does.
+The app's TCP peer is `rproxy`. The app sees the headers the TLS-terminating
+proxy sent, with that proxy's address added to `X-Forwarded-For`. So the app
+must trust `rproxy`'s address for forwarded headers. In a container of its own,
+`rproxy` is on the private network, which the usual default of a trusted-proxy
+setting covers. Beside the app, its address is `127.0.0.1` or `::1`, which the
+private ranges leave out, so the app's own setting must name them too, as
+`app.run` does.
 
 ### Checking that it works
 
@@ -185,7 +238,7 @@ does.
   `healthy` for each container of `smallwebwaf`.
 - A log line with `"msg":"starting"` gives the version, the address and every
   setting in effect, with secrets masked.
-- A request to the site through traefik gets the app's answer.
+- A request to the site through the TLS-terminating proxy gets the app's answer.
   `https://<site>/_sww/healthz` answers `ok`. `waf`'s log lines about the
   request have `"action":"forward"`.
 - To see a refusal without banning yourself, run `waf` with

SPEC.md

@@ -3,7 +3,7 @@
 `smallwebwaf` is a web application firewall for self-hosted apps. It is one
 binary, `sww`, and two of its commands do the work:
 
-- `sww rproxy` is a reverse proxy between traefik and one app.
+- `sww rproxy` is a reverse proxy between a TLS-terminating proxy and one app.
 - `sww waf` decides what happens to each request, for many sites.
 
 This document says what it must do and why, each requirement once. Everything in
@@ -45,7 +45,8 @@ never as a time.
 
 ## Non-goals
 
-- TLS, certificates and routing by host name. Those are traefik's job.
+- TLS, certificates and routing by host name. Those are the job of the
+  TLS-terminating proxy, such as traefik, nginx or Caddy.
 - More than one app behind one `rproxy`. Each app has its own.
 - Browser challenges such as captchas or proof of work. If wanted, chain Anubis
   between `rproxy` and the app.
@@ -1943,10 +1944,10 @@ leave out a cookie only when its name matches exactly, case included.
 ### Ban lengths, response and scope
 
 `SWW_WAF_BAN_RESPONSE` is `403` by default, which makes a ban easy to recognise
-when debugging; `429` and `close` are the alternatives. Behind traefik, `close`
-does not leave the client unanswered: traefik answers `502`, as it does whenever
-its backend drops a connection. `SWW_WAF_BAN_SCOPE_V4_PREFIX` widens an IPv4 ban
-to the surrounding netblock. The four ban lengths are under "Bans".
+when debugging; `429` and `close` are the alternatives. `close` does not leave
+the client unanswered: the TLS-terminating proxy answers `502`, as it does
+whenever its backend drops a connection. `SWW_WAF_BAN_SCOPE_V4_PREFIX` widens an
+IPv4 ban to the surrounding netblock. The four ban lengths are under "Bans".
 
 ### Reputation
 
@@ -2771,9 +2772,9 @@ its whole body. The visitor gets that answer at once, and the connection closes
 after it.
 
 The largest request line and headers is 32 KiB. A kept-open connection is closed
-after 120 seconds idle. Neither has a setting. traefik, by default, closes an
-unused connection after 90 seconds. So traefik closes first, and never sends a
-request on a connection `rproxy` is closing.
+after 120 seconds idle. Neither has a setting. The TLS-terminating proxy should
+close an unused connection sooner, so that it never sends a request on a
+connection `rproxy` is closing. traefik closes one after 90 seconds by default.
 
 What the visitor gets when a limit is passed:
 
@@ -2824,14 +2825,16 @@ chooses: `waf` runs `waf`, and with it unset the image runs `rproxy`.
 The usual setup is three containers on one private network:
 
 - the app;
-- `rproxy`, which traefik routes to, with `SWW_RPROXY_UPSTREAM_URL` naming the
-  app and `SWW_RPROXY_WAF_BACKEND` naming `waf`;
+- `rproxy`, which the TLS-terminating proxy forwards to, with
+  `SWW_RPROXY_UPSTREAM_URL` naming the app and `SWW_RPROXY_WAF_BACKEND` naming
+  `waf`;
 - `waf`, with `SWW_COMMAND=waf` and a volume for its state files.
 
 Each further app adds its own container and its own `rproxy`, whose
 `SWW_RPROXY_WAF_BACKEND` names the same `waf` (see "Sites"). Anything on that
 network can reach an app around `rproxy`, and can ask `waf` questions or send it
-reports. So the network holds only what you trust.
+reports. So the network holds only what you trust. `README.md` lists what the
+TLS-terminating proxy must do.
 
 ### `rproxy` in the app's container
 
@@ -2903,10 +2906,10 @@ process that stops at start is started again every second, not in a tight loop.
   container's output, which `docker logs` shows.
 - When a service exits, runit runs its `run` script again, and the container
   does not stop. Beside an app, the other process keeps running.
-- While `rproxy` is down, traefik answers `502`. While the app is down, `rproxy`
-  answers `502`, which is not a client offence. While `waf` is down,
-  `SWW_RPROXY_WAF_BACKEND_NO_ANSWER_DISPOSITION` decides (see "Without an answer
-  from `waf`").
+- While `rproxy` is down, the TLS-terminating proxy answers `502`. While the app
+  is down, `rproxy` answers `502`, which is not a client offence. While `waf` is
+  down, `SWW_RPROXY_WAF_BACKEND_NO_ANSWER_DISPOSITION` decides (see "Without an
+  answer from `waf`").
 - Only faults found at start stop `waf`:
     - invalid configuration;
     - a lookup database that is missing or unreadable;
@@ -2939,23 +2942,26 @@ checks:
 - With `SWW_COMMAND` unset, empty or `rproxy`, it passes while `rproxy` answers
   that request on `127.0.0.1`, at the port in `SWW_RPROXY_LISTEN_ADDR`, and the
   app accepts connections at `SWW_RPROXY_UPSTREAM_URL`. It does not ask `waf`,
-  so that the site stays in traefik's routes while `waf` is down.
+  so that the site stays in the TLS-terminating proxy's routes while `waf` is
+  down.
 - With any other value, it fails with a message naming `SWW_COMMAND` and its
   value.
 
-traefik sends a container no requests until it shows as healthy. So the check
-runs every second from the container's start until it first passes, for up to a
-minute, and every 30 seconds after that. An app with a health check of its own
-can replace the image's `HEALTHCHECK` with one that checks both.
+A TLS-terminating proxy that reads Docker's health status, as traefik does,
+sends a container no requests until it shows as healthy. So the check runs every
+second from the container's start until it first passes, for up to a minute, and
+every 30 seconds after that. An app with a health check of its own can replace
+the image's `HEALTHCHECK` with one that checks both.
 
 ### Ports
 
 `rproxy` listens on no port but the one in `SWW_RPROXY_LISTEN_ADDR`, 8080 by
-default, which traefik routes to. It passes requests to the app at
-`SWW_RPROXY_UPSTREAM_URL`, `http://127.0.0.1:8081` by default. Another port may
-be set: the health check follows the setting, and traefik's port label
-(`traefik.http.services.<name>.loadbalancer.server.port`) must name it. An app
-beside `rproxy` must leave that port free.
+default, which the TLS-terminating proxy forwards to. It passes requests to the
+app at `SWW_RPROXY_UPSTREAM_URL`, `http://127.0.0.1:8081` by default. Another
+port may be set: the health check follows the setting, and the TLS-terminating
+proxy must name it, as traefik's port label
+(`traefik.http.services.<name>.loadbalancer.server.port`) does. An app beside
+`rproxy` must leave that port free.
 
 `waf` listens on no port but the one in `SWW_WAF_LISTEN_ADDR`, 8080 by default.
 The questions, the reports and its own endpoints all come there.
@@ -2996,9 +3002,9 @@ in `docs/settings.md` shows the commands.
 ### Forwarded headers
 
 The app's TCP peer is `rproxy`, and the `X-Forwarded-For` the app receives ends
-with traefik's address, which `rproxy` adds after the visitor's. So the app must
-trust `rproxy`'s address for forwarded headers, besides the private address
-ranges traefik is on.
+with the TLS-terminating proxy's address, which `rproxy` adds after the
+visitor's. So the app must trust `rproxy`'s address for forwarded headers,
+besides the private address ranges the TLS-terminating proxy is on.
 
 - In a container of its own, `rproxy`'s address is on the private network. The
   usual default for a trusted-proxy setting, the private ranges, covers it.

docs/request-log.md

@@ -68,7 +68,8 @@ Every one of these lines has:
 ### Request detail
 
 - `request_id`: the id `rproxy` made for the request when it arrived.
-- `peer_ip`: the address of `rproxy`'s TCP peer, normally traefik.
+- `peer_ip`: the address of `rproxy`'s TCP peer, normally the TLS-terminating
+  proxy.
 - `forwarded_for`: the `X-Forwarded-For` header the visitor's request came with.
 - `client_group`: the client as rate limiting counts it, an IPv4 address as a
   /32 or an IPv6 group.

docs/settings.md

@@ -478,9 +478,9 @@ start, and an invalid value stops the start. Any can be given as a file, as a
   `10.0.0.0/8,172.16.0.0/12,192.168.0.0/16`): the netblocks whose
   `X-Forwarded-For` is believed. Set but empty, it trusts nothing. A client
   outside these netblocks cannot claim another address. Where other containers
-  reach `rproxy` directly, or visitors on a private network reach traefik, they
-  can name another address in the header. Narrowing the setting to traefik's own
-  network closes that gap.
+  reach `rproxy` directly, or visitors on a private network reach the
+  TLS-terminating proxy, they can name another address in the header. Narrowing
+  the setting to the TLS-terminating proxy's own network closes that gap.
 
 ## The image's command