Graham McIntire
ab2c28c595
- WebSocket: reject frames exceeding 16 MB to prevent OOM - MikroTik: reject words exceeding 10 MB to prevent OOM - Self-update: require HTTPS for download URLs - Self-update: require non-empty SHA256 checksum - Self-update: use constant-time comparison for checksum verification - Self-update: bound download size to 100 MB
83 lines
2.2 KiB
Go
83 lines
2.2 KiB
Go
package main
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import (
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"crypto/sha256"
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"crypto/subtle"
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"fmt"
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"io"
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"log/slog"
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"net/http"
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"net/url"
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"os"
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"syscall"
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)
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var osExecutable = os.Executable
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var osWriteFile = os.WriteFile
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var osRename = os.Rename
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var httpGet = http.Get
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var maxUpdateSize int64 = 100 << 20 // 100 MB
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// selfUpdate downloads a new binary, verifies its checksum, replaces the current binary, and re-execs.
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func selfUpdate(downloadURL, expectedChecksum string) error {
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u, err := url.Parse(downloadURL)
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if err != nil {
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return fmt.Errorf("parse url: %w", err)
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}
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if u.Scheme != "https" {
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return fmt.Errorf("HTTPS required for update URL, got %q", u.Scheme)
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}
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if expectedChecksum == "" {
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return fmt.Errorf("checksum required for update")
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}
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slog.Info("downloading update", "url", downloadURL)
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resp, err := httpGet(downloadURL)
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if err != nil {
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return fmt.Errorf("download: %w", err)
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}
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defer func() { _ = resp.Body.Close() }()
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if resp.StatusCode != http.StatusOK {
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return fmt.Errorf("download failed: status %d", resp.StatusCode)
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}
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body, err := io.ReadAll(io.LimitReader(resp.Body, maxUpdateSize+1))
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if err != nil {
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return fmt.Errorf("read body: %w", err)
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}
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if int64(len(body)) > maxUpdateSize {
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return fmt.Errorf("download size %d exceeds max %d", len(body), maxUpdateSize)
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}
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slog.Info("downloaded update", "bytes", len(body))
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// Verify SHA256 checksum (constant-time comparison)
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actual := fmt.Sprintf("%x", sha256.Sum256(body))
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if subtle.ConstantTimeCompare([]byte(actual), []byte(expectedChecksum)) != 1 {
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return fmt.Errorf("checksum mismatch: expected %s, got %s", expectedChecksum, actual)
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}
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slog.Info("checksum verified")
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// Write to temp file next to current binary
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currentExe, err := osExecutable()
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if err != nil {
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return fmt.Errorf("get executable path: %w", err)
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}
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tempPath := currentExe + ".update"
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if err := osWriteFile(tempPath, body, 0755); err != nil {
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return fmt.Errorf("write temp: %w", err)
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}
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// Replace current binary
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if err := osRename(tempPath, currentExe); err != nil {
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_ = os.Remove(tempPath)
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return fmt.Errorf("rename: %w", err)
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}
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slog.Info("binary replaced", "path", currentExe)
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// Re-exec with same arguments
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slog.Info("re-executing", "args", os.Args)
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return syscall.Exec(currentExe, os.Args, os.Environ())
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}
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