From 04106d15d5ad73db6e670e84340ac1f9be200a23 Mon Sep 17 00:00:00 2001
From: garethgeorge <garethgeorge97@gmail.com>
Date: Mon, 15 Jan 2024 14:02:07 -0800
Subject: [PATCH] feat: verify gpg signature when downloading and installing
 restic binary

---
 internal/resticinstaller/resticinstaller.go | 137 ++++++++++----
 internal/resticinstaller/verify.go          | 188 ++++++++++++++++++++
 scripts/latest-restic-version.sh            |   6 +
 3 files changed, 298 insertions(+), 33 deletions(-)
 create mode 100644 internal/resticinstaller/verify.go
 create mode 100755 scripts/latest-restic-version.sh

diff --git a/internal/resticinstaller/resticinstaller.go b/internal/resticinstaller/resticinstaller.go
index 5c477a2d..ef8a9adb 100644
--- a/internal/resticinstaller/resticinstaller.go
+++ b/internal/resticinstaller/resticinstaller.go
@@ -4,6 +4,9 @@ import (
 	"archive/zip"
 	"bytes"
 	"compress/bzip2"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"io"
@@ -36,68 +39,122 @@ func resticDownloadURL(version string) string {
 	return fmt.Sprintf("https://github.com/restic/restic/releases/download/v%v/restic_%v_%v_%v.bz2", version, version, runtime.GOOS, runtime.GOARCH)
 }
 
-func downloadFile(url string, downloadPath string) error {
-	// Download ur as a file and save it to path
+func hashDownloadURL(version string) string {
+	return fmt.Sprintf("https://github.com/restic/restic/releases/download/v%v/SHA256SUMS", version)
+}
+
+func sigDownloadURL(version string) string {
+	return fmt.Sprintf("https://github.com/restic/restic/releases/download/v%v/SHA256SUMS.asc", version)
+}
+
+// getURL downloads the given url and returns the response body as a string.
+func getURL(url string) ([]byte, error) {
 	resp, err := http.Get(url)
 	if err != nil {
-		return fmt.Errorf("http GET %v: %w", url, err)
+		return nil, fmt.Errorf("http GET %v: %w", url, err)
+	}
+	defer resp.Body.Close()
+
+	var body bytes.Buffer
+	_, err = io.Copy(&body, resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("copy response body to buffer: %w", err)
+	}
+	return body.Bytes(), nil
+}
+
+func verify(sha256 string) error {
+	sha256sums, err := getURL(hashDownloadURL(RequiredResticVersion))
+	if err != nil {
+		return fmt.Errorf("get sha256sums: %w", err)
+	}
+
+	signature, err := getURL(sigDownloadURL(RequiredResticVersion))
+	if err != nil {
+		return fmt.Errorf("get signature: %w", err)
+	}
+
+	if ok, err := gpgVerify(sha256sums, signature); !ok || err != nil {
+		return fmt.Errorf("gpg verification failed: ok=%v err=%v", ok, err)
+	}
+
+	if !strings.Contains(string(sha256sums), sha256) {
+		fmt.Fprintf(os.Stderr, "sha256sums:\n%v\n", string(sha256sums))
+		return fmt.Errorf("sha256sums do not contain %v", sha256)
+	}
+
+	return nil
+}
+
+// downloadFile downloads a file from the given url and saves it to the given path. The sha256 checksum of the file is returned on success.
+func downloadFile(url string, downloadPath string) (string, error) {
+	// Download ur as a file and save it to path
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodGet, url, nil)
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Accept", "application/octet-stream")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("http GET %v: %w", url, err)
 	}
 	defer resp.Body.Close()
 
-	var body io.Reader = resp.Body
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("http GET %v: %v", url, resp.Status)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", fmt.Errorf("read response body: %w", err)
+	}
+	hash := sha256.Sum256(body)
+
 	if strings.HasSuffix(url, ".bz2") {
-		body = bzip2.NewReader(resp.Body)
+		body, err = io.ReadAll(bzip2.NewReader(bytes.NewReader(body)))
+		if err != nil {
+			return "", fmt.Errorf("bz2 decompress body: %w", err)
+		}
 	} else if strings.HasSuffix(url, ".zip") {
 		var fullBody bytes.Buffer
 		_, err := io.Copy(&fullBody, resp.Body)
 		if err != nil {
-			return fmt.Errorf("copy response body to buffer: %w", err)
+			return "", fmt.Errorf("copy response body to buffer: %w", err)
 		}
 
 		archive, err := zip.NewReader(bytes.NewReader(fullBody.Bytes()), int64(fullBody.Len()))
 		if err != nil {
-			return fmt.Errorf("open zip archive: %w", err)
+			return "", fmt.Errorf("open zip archive: %w", err)
 		}
 
 		if len(archive.File) != 1 {
-			return fmt.Errorf("expected zip archive to contain exactly one file, got %v", len(archive.File))
+			return "", fmt.Errorf("expected zip archive to contain exactly one file, got %v", len(archive.File))
+		}
+		f, err := archive.File[0].Open()
+		if err != nil {
+			return "", fmt.Errorf("open zip archive file %v: %w", archive.File[0].Name, err)
 		}
-		body, err = archive.File[0].Open()
+
+		body, err = io.ReadAll(f)
 		if err != nil {
-			return fmt.Errorf("open zip archive file %v: %w", archive.File[0].Name, err)
+			return "", fmt.Errorf("read zip archive file %v: %w", archive.File[0].Name, err)
 		}
 	}
 
 	out, err := os.Create(downloadPath)
 	if err != nil {
-		return fmt.Errorf("create file %v: %w", downloadPath, err)
+		return "", fmt.Errorf("create file %v: %w", downloadPath, err)
 	}
 	defer out.Close()
 	if err != nil {
-		return fmt.Errorf("create file %v: %w", downloadPath, err)
+		return "", fmt.Errorf("create file %v: %w", downloadPath, err)
 	}
-	_, err = io.Copy(out, body)
+	_, err = io.Copy(out, bytes.NewReader(body))
 	if err != nil {
-		return fmt.Errorf("copy response body to file %v: %w", downloadPath, err)
-	}
-
-	return nil
-}
-
-func downloadExecutable(url string, path string) error {
-	if err := downloadFile(url, path+".tmp"); err != nil {
-		return err
-	}
-
-	if err := os.Chmod(path+".tmp", 0755); err != nil {
-		return fmt.Errorf("chmod executable %v: %w", path, err)
+		return "", fmt.Errorf("copy response body to file %v: %w", downloadPath, err)
 	}
 
-	if err := os.Rename(path+".tmp", path); err != nil {
-		return fmt.Errorf("rename %v.tmp to %v: %w", path, path, err)
-	}
-
-	return nil
+	return hex.EncodeToString(hash[:]), nil
 }
 
 func installResticIfNotExists(resticInstallPath string) error {
@@ -112,8 +169,22 @@ func installResticIfNotExists(resticInstallPath string) error {
 			return fmt.Errorf("create restic install directory %v: %w", path.Dir(resticInstallPath), err)
 		}
 
-		if err := downloadExecutable(resticDownloadURL(RequiredResticVersion), resticInstallPath); err != nil {
-			return fmt.Errorf("download restic version %v: %w", RequiredResticVersion, err)
+		hash, err := downloadFile(resticDownloadURL(RequiredResticVersion), resticInstallPath+".tmp")
+		if err != nil {
+			return err
+		}
+
+		if err := verify(hash); err != nil {
+			os.Remove(resticInstallPath) // try to remove the bad binary.
+			return fmt.Errorf("failed to verify the authenticity of the downloaded restic binary: %v", err)
+		}
+
+		if err := os.Chmod(resticInstallPath+".tmp", 0755); err != nil {
+			return fmt.Errorf("chmod executable %v: %w", resticInstallPath, err)
+		}
+
+		if err := os.Rename(resticInstallPath+".tmp", resticInstallPath); err != nil {
+			return fmt.Errorf("rename %v.tmp to %v: %w", resticInstallPath, resticInstallPath, err)
 		}
 
 		return nil
diff --git a/internal/resticinstaller/verify.go b/internal/resticinstaller/verify.go
new file mode 100644
index 00000000..49610a44
--- /dev/null
+++ b/internal/resticinstaller/verify.go
@@ -0,0 +1,188 @@
+package resticinstaller
+
+// Original implementation in restic: https://github.com/restic/restic/blob/master/internal/selfupdate/verify.go
+
+import (
+	"bytes"
+	"fmt"
+
+	"golang.org/x/crypto/openpgp"
+)
+
+var key = []byte(`
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=AV20
+-----END PGP PUBLIC KEY BLOCK-----
+`)
+
+// gpgVerify checks the authenticity of data by verifying the signature sig,
+// which must be ASCII armored (base64). When the signature matches, GPGVerify
+// returns true and a nil error.
+func gpgVerify(data, sig []byte) (ok bool, err error) {
+	keyring, err := openpgp.ReadArmoredKeyRing(bytes.NewReader(key))
+	if err != nil {
+		return false, fmt.Errorf("read keyring fialed: %w", err)
+	}
+
+	_, err = openpgp.CheckArmoredDetachedSignature(keyring, bytes.NewReader(data), bytes.NewReader(sig))
+	if err != nil {
+		return false, err
+	}
+
+	return true, nil
+}
diff --git a/scripts/latest-restic-version.sh b/scripts/latest-restic-version.sh
new file mode 100755
index 00000000..e11a6eca
--- /dev/null
+++ b/scripts/latest-restic-version.sh
@@ -0,0 +1,6 @@
+#!/bin/bash
+
+curl -s https://api.github.com/repos/restic/restic/releases/latest \
+| grep "https://api.github.com/repos/restic/restic/tarball/" \
+| sed -E 's/.*v([0-9]+\.[0-9]+\.[0-9]+).*/\1/
+