From c1631b0a39d34267345b41214f1f5e8a77d98cd2 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 23 Sep 2024 15:09:44 +0200 Subject: [PATCH 1/2] [security] 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. (cherry picked from commit c04bc17a5a0fdcb725a11ef6541f94730112e7b6) (cherry picked from commit f2f47fa725fc87bfb536de171a2ea81f2789c9fb) (cherry picked from commit 7b39cd631e0d3c3d238015c6f450c59bbc9cbc5b) Upstream-PR: https://github.com/NixOS/nix/pull/11585 Change-Id: Ia973420f6098113da05a594d48394ce1fe41fbb9 --- doc/manual/rl-next/verify-tls.md | 10 ++++ src/libstore/builtins/fetchurl.cc | 3 -- tests/nixos/default.nix | 2 + tests/nixos/fetchurl.nix | 78 +++++++++++++++++++++++++++++++ 4 files changed, 90 insertions(+), 3 deletions(-) create mode 100644 doc/manual/rl-next/verify-tls.md create mode 100644 tests/nixos/fetchurl.nix diff --git a/doc/manual/rl-next/verify-tls.md b/doc/manual/rl-next/verify-tls.md new file mode 100644 index 000000000..608f3347e --- /dev/null +++ b/doc/manual/rl-next/verify-tls.md @@ -0,0 +1,10 @@ +--- +synopsis: "`` now uses TLS verification" +category: Fixes +prs: [11585] +credits: edolstra +--- + +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 issue. diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc index 062ecdc14..3fb769fe6 100644 --- a/src/libstore/builtins/fetchurl.cc +++ b/src/libstore/builtins/fetchurl.cc @@ -33,10 +33,7 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData) auto fetch = [&](const std::string & url) { - /* No need to do TLS verification, because we check the hash of - the result anyway. */ FileTransferRequest request(url); - request.verifyTLS = false; auto raw = fileTransfer->download(std::move(request)); auto decompressor = makeDecompressionSource( diff --git a/tests/nixos/default.nix b/tests/nixos/default.nix index 20e66f6c1..2d6eaed16 100644 --- a/tests/nixos/default.nix +++ b/tests/nixos/default.nix @@ -157,4 +157,6 @@ in coredumps = runNixOSTestFor "x86_64-linux" ./coredumps; io_uring = runNixOSTestFor "x86_64-linux" ./io_uring; + + 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..63c639c31 --- /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 "$out/cert.pem" -noenc + ''; + + goodCert = makeTlsCert "good"; + badCert = makeTlsCert "bad"; + +in + +{ + name = "fetchurl"; + + nodes = { + machine = { lib, pkgs, ... }: { + services.nginx = { + enable = true; + + virtualHosts."good" = { + addSSL = true; + sslCertificate = "${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 or "SSL peer certificate or SSH remote key was not OK" in err + ''; +} From 37b22dae04f2da214e6b9bef3427e134280642ca Mon Sep 17 00:00:00 2001 From: Puck Meerburg Date: Thu, 26 Sep 2024 15:12:24 +0000 Subject: [PATCH 2/2] Fix passing custom CA files into the builtin:fetchurl sandbox Without this, verifying TLS certificates would fail on macOS, as well as any system that doesn't have a certificate file at /etc/ssl/certs/ca-certificates.crt, which includes e.g. Fedora. Change-Id: Iaa2e0e9db3747645b5482c82e3e0e4e8f229f5f9 --- src/libstore/build/local-derivation-goal.cc | 19 +++++++++++++------ src/libstore/builtins.hh | 2 +- src/libstore/builtins/fetchurl.cc | 5 ++++- tests/nixos/fetchurl.nix | 6 ++++++ 4 files changed, 24 insertions(+), 8 deletions(-) diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc index 4baa525d9..f14d09652 100644 --- a/src/libstore/build/local-derivation-goal.cc +++ b/src/libstore/build/local-derivation-goal.cc @@ -1361,13 +1361,20 @@ void LocalDerivationGoal::runChild() bool setUser = true; - /* Make the contents of netrc available to builtin:fetchurl - (which may run under a different uid and/or in a sandbox). */ + /* Make the contents of netrc and the CA certificate bundle + available to builtin:fetchurl (which may run under a + different uid and/or in a sandbox). */ std::string netrcData; - try { - if (drv->isBuiltin() && drv->builder == "builtin:fetchurl" && !derivationType->isSandboxed()) + std::string caFileData; + if (drv->isBuiltin() && drv->builder == "builtin:fetchurl" && !derivationType->isSandboxed()) { + try { netrcData = readFile(settings.netrcFile); - } catch (SysError &) { } + } catch (SysError &) { } + + try { + caFileData = readFile(settings.caFile); + } catch (SysError &) { } + } #if __linux__ if (useChroot) { @@ -1802,7 +1809,7 @@ void LocalDerivationGoal::runChild() e.second = rewriteStrings(e.second, inputRewrites); if (drv->builder == "builtin:fetchurl") - builtinFetchurl(drv2, netrcData); + builtinFetchurl(drv2, netrcData, caFileData); else if (drv->builder == "builtin:buildenv") builtinBuildenv(drv2); else if (drv->builder == "builtin:unpack-channel") diff --git a/src/libstore/builtins.hh b/src/libstore/builtins.hh index d201fb3ac..e20d14b90 100644 --- a/src/libstore/builtins.hh +++ b/src/libstore/builtins.hh @@ -6,7 +6,7 @@ namespace nix { // TODO: make pluggable. -void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData); +void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData, const std::string & caFileData); void builtinUnpackChannel(const BasicDerivation & drv); } diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc index 3fb769fe6..b28eb01d0 100644 --- a/src/libstore/builtins/fetchurl.cc +++ b/src/libstore/builtins/fetchurl.cc @@ -7,7 +7,7 @@ namespace nix { -void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData) +void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData, const std::string & caFileData) { /* Make the host's netrc data available. Too bad curl requires this to be stored in a file. It would be nice if we could just @@ -17,6 +17,9 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData) writeFile(settings.netrcFile, netrcData, 0600); } + settings.caFile = "ca-certificates.crt"; + writeFile(settings.caFile, caFileData, 0600); + auto getAttr = [&](const std::string & name) { auto i = drv.env.find(name); if (i == drv.env.end()) throw Error("attribute '%s' missing", name); diff --git a/tests/nixos/fetchurl.nix b/tests/nixos/fetchurl.nix index 63c639c31..97365d053 100644 --- a/tests/nixos/fetchurl.nix +++ b/tests/nixos/fetchurl.nix @@ -67,6 +67,9 @@ in out = machine.succeed("curl https://good/index.html") assert out == "hello world\n" + out = machine.succeed("cat ${badCert}/cert.pem > /tmp/cafile.pem; curl --cacert /tmp/cafile.pem https://bad/index.html") + assert out == "foobar\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=\"; }'") @@ -74,5 +77,8 @@ in 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 or "SSL peer certificate or SSH remote key was not OK" in err + + # Fetching from a server with a trusted cert should work via environment variable override. + machine.succeed("NIX_SSL_CERT_FILE=/tmp/cafile.pem nix build --no-substitute --expr 'import { url = \"https://bad/index.html\"; hash = \"sha256-rsBwZF/lPuOzdjBZN2E08FjMM3JHyXit0Xi2zN+wAZ8=\"; }'") ''; }