From c04bc17a5a0fdcb725a11ef6541f94730112e7b6 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 23 Sep 2024 15:09:44 +0200 Subject: [PATCH 1/3] builtin:fetchurl: Enable TLS verification This is better for privacy and to avoid leaking netrc credentials in a MITM attack, but also the assumption that we check the hash no longer holds in some cases (in particular for impure derivations). Partially reverts https://github.com/NixOS/nix/commit/5db358d4d78aea7204a8f22c5bf2a309267ee038. --- src/libstore/builtins/fetchurl.cc | 3 --- 1 file changed, 3 deletions(-) diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc index b9dfeba2f..f33060c33 100644 --- a/src/libstore/builtins/fetchurl.cc +++ b/src/libstore/builtins/fetchurl.cc @@ -38,10 +38,7 @@ void builtinFetchurl( auto source = sinkToSource([&](Sink & sink) { - /* No need to do TLS verification, because we check the hash of - the result anyway. */ FileTransferRequest request(url); - request.verifyTLS = false; request.decompress = false; auto decompressor = makeDecompressionSink( From f2f47fa725fc87bfb536de171a2ea81f2789c9fb Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Tue, 24 Sep 2024 16:13:28 +0200 Subject: [PATCH 2/3] Add a test for builtin:fetchurl cert verification --- tests/nixos/default.nix | 2 ++ tests/nixos/fetchurl.nix | 78 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 80 insertions(+) create mode 100644 tests/nixos/fetchurl.nix diff --git a/tests/nixos/default.nix b/tests/nixos/default.nix index 62fc6b10f..c61a2888f 100644 --- a/tests/nixos/default.nix +++ b/tests/nixos/default.nix @@ -159,4 +159,6 @@ in fsync = runNixOSTestFor "x86_64-linux" ./fsync.nix; cgroups = runNixOSTestFor "x86_64-linux" ./cgroups; + + fetchurl = runNixOSTestFor "x86_64-linux" ./fetchurl.nix; } diff --git a/tests/nixos/fetchurl.nix b/tests/nixos/fetchurl.nix new file mode 100644 index 000000000..476f779bc --- /dev/null +++ b/tests/nixos/fetchurl.nix @@ -0,0 +1,78 @@ +# Test whether builtin:fetchurl properly performs TLS certificate +# checks on HTTPS servers. + +{ lib, config, pkgs, ... }: + +let + + makeTlsCert = name: pkgs.runCommand name { + nativeBuildInputs = with pkgs; [ openssl ]; + } '' + mkdir -p $out + openssl req -x509 \ + -subj '/CN=${name}/' -days 49710 \ + -addext 'subjectAltName = DNS:${name}' \ + -keyout "$out/key.pem" -newkey ed25519 \ + -out "$out/cert.pem" -noenc + ''; + + goodCert = makeTlsCert "good"; + badCert = makeTlsCert "bad"; + +in + +{ + name = "nss-preload"; + + nodes = { + machine = { lib, pkgs, ... }: { + services.nginx = { + enable = true; + + virtualHosts."good" = { + addSSL = true; + sslCertificate = "${goodCert}/cert.pem"; + sslCertificateKey = "${goodCert}/key.pem"; + root = pkgs.runCommand "nginx-root" {} '' + mkdir "$out" + echo 'hello world' > "$out/index.html" + ''; + }; + + virtualHosts."bad" = { + addSSL = true; + sslCertificate = "${badCert}/cert.pem"; + sslCertificateKey = "${badCert}/key.pem"; + root = pkgs.runCommand "nginx-root" {} '' + mkdir "$out" + echo 'foobar' > "$out/index.html" + ''; + }; + }; + + security.pki.certificateFiles = [ "${goodCert}/cert.pem" ]; + + networking.hosts."127.0.0.1" = [ "good" "bad" ]; + + virtualisation.writableStore = true; + + nix.settings.experimental-features = "nix-command"; + }; + }; + + testScript = { nodes, ... }: '' + machine.wait_for_unit("nginx") + machine.wait_for_open_port(443) + + out = machine.succeed("curl https://good/index.html") + assert out == "hello world\n" + + # Fetching from a server with a trusted cert should work. + machine.succeed("nix build --no-substitute --expr 'import { url = \"https://good/index.html\"; hash = \"sha256-qUiQTy8PR5uPgZdpSzAYSw0u0cHNKh7A+4XSmaGSpEc=\"; }'") + + # Fetching from a server with an untrusted cert should fail. + err = machine.fail("nix build --no-substitute --expr 'import { url = \"https://bad/index.html\"; hash = \"sha256-rsBwZF/lPuOzdjBZN2E08FjMM3JHyXit0Xi2zN+wAZ8=\"; }' 2>&1") + print(err) + assert "SSL certificate problem: self-signed certificate" in err + ''; +} From 7b39cd631e0d3c3d238015c6f450c59bbc9cbc5b Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Wed, 25 Sep 2024 22:33:50 +0200 Subject: [PATCH 3/3] Add release note --- doc/manual/rl-next/verify-tls.md | 8 ++++++++ 1 file changed, 8 insertions(+) create mode 100644 doc/manual/rl-next/verify-tls.md diff --git a/doc/manual/rl-next/verify-tls.md b/doc/manual/rl-next/verify-tls.md new file mode 100644 index 000000000..489941d5b --- /dev/null +++ b/doc/manual/rl-next/verify-tls.md @@ -0,0 +1,8 @@ +--- +synopsis: "`` uses TLS verification" +prs: [11585] +--- + +Previously `` did not do TLS verification. This was because the Nix sandbox in the past did not have access to TLS certificates, and Nix checks the hash of the fetched file anyway. However, this can expose authentication data from `netrc` and URLs to man-in-the-middle attackers. In addition, Nix now in some cases (such as when using impure derivations) does *not* check the hash. Therefore we have now enabled TLS verification. This means that downloads by `` will now fail if you're fetching from a HTTPS server that does not have a valid certificate. + +`` is also known as the builtin derivation builder `builtin:fetchurl`. It's not to be confused with the evaluation-time function `builtins.fetchurl`, which was not affected by this issues.