lohr: validate webhook signature

Previously lohr was unusable in a production setting, anyone could forge
a malicious webhook and either:

- mirror a private repo of yours to another remote they own
- wipe a repo of yours by forcing mirroring from an empty mirror

This is no longer the case!
This commit is contained in:
Antoine Martin 2021-03-30 11:23:09 +02:00
parent 7134b7700f
commit 7e3c8b8f28
5 changed files with 156 additions and 5 deletions

10
Cargo.lock generated
View file

@ -336,6 +336,12 @@ dependencies = [
"libc", "libc",
] ]
[[package]]
name = "hex"
version = "0.4.3"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
[[package]] [[package]]
name = "hkdf" name = "hkdf"
version = "0.10.0" version = "0.10.0"
@ -494,11 +500,15 @@ name = "lohr"
version = "0.2.1" version = "0.2.1"
dependencies = [ dependencies = [
"anyhow", "anyhow",
"hex",
"hmac",
"log 0.4.14", "log 0.4.14",
"rocket", "rocket",
"rocket_contrib", "rocket_contrib",
"serde", "serde",
"serde_json",
"serde_yaml", "serde_yaml",
"sha2",
] ]
[[package]] [[package]]

View file

@ -12,8 +12,12 @@ repository = "https://github.com/alarsyo/lohr"
[dependencies] [dependencies]
anyhow = "1.0.40" anyhow = "1.0.40"
hex = "0.4.3"
hmac = "0.10.1"
log = "0.4.14" log = "0.4.14"
rocket = "0.4.7" rocket = "0.4.7"
rocket_contrib = { version = "0.4.7", features = [ "json" ] } rocket_contrib = { version = "0.4.7", features = [ "json" ] }
serde = { version = "1.0.125", features = [ "derive" ] } serde = { version = "1.0.125", features = [ "derive" ] }
serde_json = "1.0.64"
serde_yaml = "0.8.17" serde_yaml = "0.8.17"
sha2 = "0.9.3"

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@ -29,20 +29,28 @@ Setting up =lohr= should be quite simple:
1. Create a =Rocket.toml= file and [[https://rocket.rs/v0.4/guide/configuration/][add your configuration]]. 1. Create a =Rocket.toml= file and [[https://rocket.rs/v0.4/guide/configuration/][add your configuration]].
2. Run =lohr=: 2. Export a secret variable:
#+begin_src sh
$ export LOHR_SECRET=42 # please don't use this secret
#+end_src
3. Run =lohr=:
#+begin_src sh #+begin_src sh
$ cargo run # or `cargo run --release` for production usage $ cargo run # or `cargo run --release` for production usage
#+end_src #+end_src
3. Configure your favorite git server to send a webhook to =lohr='s address on 4. Configure your favorite git server to send a webhook to =lohr='s address on
every push event. every push event.
I used [[https://docs.gitea.io/en-us/webhooks/][Gitea's webhooks format]], but I *think* they're similar to GitHub and I used [[https://docs.gitea.io/en-us/webhooks/][Gitea's webhooks format]], but I *think* they're similar to GitHub and
GitLab's webhooks, so these should work too! (If they don't, *please* file an GitLab's webhooks, so these should work too! (If they don't, *please* file an
issue!) issue!)
4. Add a =.lohr= file containing the remotes you want to mirror this repo to: Don't forget to set the webhook secret to the one you chose above.
5. Add a =.lohr= file containing the remotes you want to mirror this repo to:
#+begin_example #+begin_example
git@github.com:you/your_repo git@github.com:you/your_repo

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@ -10,7 +10,6 @@ use std::sync::{
use std::thread; use std::thread;
use rocket::{http::Status, post, routes, State}; use rocket::{http::Status, post, routes, State};
use rocket_contrib::json::Json;
use log::error; use log::error;
@ -23,10 +22,14 @@ use job::Job;
mod settings; mod settings;
use settings::GlobalSettings; use settings::GlobalSettings;
mod signature;
use signature::SignedJson;
struct JobSender(Mutex<Sender<Job>>); struct JobSender(Mutex<Sender<Job>>);
struct Secret(String);
#[post("/", data = "<payload>")] #[post("/", data = "<payload>")]
fn gitea_webhook(payload: Json<GiteaWebHook>, sender: State<JobSender>) -> Status { fn gitea_webhook(payload: SignedJson<GiteaWebHook>, sender: State<JobSender>) -> Status {
// TODO: validate Gitea signature // TODO: validate Gitea signature
{ {
@ -66,6 +69,9 @@ fn main() -> anyhow::Result<()> {
let homedir: PathBuf = homedir.into(); let homedir: PathBuf = homedir.into();
let homedir = homedir.canonicalize().expect("LOHR_HOME isn't valid!"); let homedir = homedir.canonicalize().expect("LOHR_HOME isn't valid!");
let secret = env::var("LOHR_SECRET")
.expect("please provide a secret, otherwise anyone can send you a malicious webhook");
let config = parse_config(homedir.clone())?; let config = parse_config(homedir.clone())?;
thread::spawn(move || { thread::spawn(move || {
@ -75,6 +81,7 @@ fn main() -> anyhow::Result<()> {
rocket::ignite() rocket::ignite()
.mount("/", routes![gitea_webhook]) .mount("/", routes![gitea_webhook])
.manage(JobSender(Mutex::new(sender))) .manage(JobSender(Mutex::new(sender)))
.manage(Secret(secret))
.launch(); .launch();
Ok(()) Ok(())

122
src/signature.rs Normal file
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@ -0,0 +1,122 @@
use std::{
io::{Read, Write},
ops::{Deref, DerefMut},
};
use rocket::{
data::{FromData, Outcome},
http::ContentType,
State,
};
use rocket::{
data::{Transform, Transformed},
http::Status,
};
use rocket::{Data, Request};
use anyhow::anyhow;
use serde::Deserialize;
use crate::Secret;
const X_GITEA_SIGNATURE: &str = "X-Gitea-Signature";
fn validate_signature(secret: &str, signature: &str, data: &str) -> bool {
use hmac::{Hmac, Mac, NewMac};
use sha2::Sha256;
type HmacSha256 = Hmac<Sha256>;
let mut mac = HmacSha256::new_varkey(secret.as_bytes()).expect("this should never fail");
mac.update(data.as_bytes());
match hex::decode(signature) {
Ok(bytes) => mac.verify(&bytes).is_ok(),
Err(_) => false,
}
}
pub struct SignedJson<T>(pub T);
impl<T> Deref for SignedJson<T> {
type Target = T;
fn deref(&self) -> &T {
&self.0
}
}
impl<T> DerefMut for SignedJson<T> {
fn deref_mut(&mut self) -> &mut T {
&mut self.0
}
}
const LIMIT: u64 = 1 << 20;
// This is a one to one implementation of request_contrib::Json's FromData, but with HMAC
// validation.
//
// Tracking issue for chaining Data guards to avoid this:
// https://github.com/SergioBenitez/Rocket/issues/775
impl<'a, T> FromData<'a> for SignedJson<T>
where
T: Deserialize<'a>,
{
type Error = anyhow::Error;
type Owned = String;
type Borrowed = str;
fn transform(
request: &Request,
data: Data,
) -> rocket::data::Transform<Outcome<Self::Owned, Self::Error>> {
let size_limit = request.limits().get("json").unwrap_or(LIMIT);
let mut s = String::with_capacity(512);
match data.open().take(size_limit).read_to_string(&mut s) {
Ok(_) => Transform::Borrowed(Outcome::Success(s)),
Err(e) => Transform::Borrowed(Outcome::Failure((
Status::BadRequest,
anyhow!("couldn't read json: {}", e),
))),
}
}
fn from_data(request: &Request, o: Transformed<'a, Self>) -> Outcome<Self, Self::Error> {
let json_ct = ContentType::new("application", "json");
if request.content_type() != Some(&json_ct) {
return Outcome::Failure((Status::BadRequest, anyhow!("wrong content type")));
}
let signatures = request.headers().get(X_GITEA_SIGNATURE).collect::<Vec<_>>();
if signatures.len() != 1 {
return Outcome::Failure((
Status::BadRequest,
anyhow!("request header needs exactly one signature"),
));
}
let signature = signatures[0];
let content = o.borrowed()?;
let secret = request.guard::<State<Secret>>().unwrap();
if !validate_signature(&secret.0, &signature, content) {
return Outcome::Failure((Status::BadRequest, anyhow!("couldn't verify signature")));
}
let content = match serde_json::from_str(content) {
Ok(content) => content,
Err(e) => {
return Outcome::Failure((
Status::BadRequest,
anyhow!("couldn't parse json: {}", e),
))
}
};
Outcome::Success(SignedJson(content))
}
}