G307: Unsafe defer call of a method returning an error for `defer file.Close()` ?

[koddr]

Summary

After update to latest Golang & gosec version, I see this security error:

[...] - G307 (CWE-703): Deferring unsafe method "Close" on type "*os.File" (Confidence: HIGH, Severity: MEDIUM)
    49:         }
  > 50:         defer file.Close()
    51: 

Summary:
   Files: 6
   Lines: 231
   Nosec: 0
   Issues: 1

My function never changes and looks like:

// ...

// NewConfig returns a new decoded Config struct
func NewConfig(configPath string) (*Config, error) {
	// Validate config path
	if err := ValidateConfigPath(configPath); err != nil {
		return nil, err
	}

	// Create config structure
	config := &Config{}

	// Open config file
	file, err := os.Open(filepath.Clean(configPath))
	if err != nil {
		return nil, err
	}
	defer file.Close() // <-- error G307 (CWE-703) on this line

	// Init new YAML decode
	d := yaml.NewDecoder(file)

	// Start YAML decoding from file
	if err := d.Decode(&config); err != nil {
		return nil, err
	}

	return config, nil
}

// ...

Steps to reproduce the behavior

1. Create function with open/close file
2. Run gosec

gosec version

$ gosec

VERSION: 2.4.0
GIT TAG: v2.4.0
BUILD DATE: 2020-07-24T07:54:54Z

Go version (output of 'go version')

go version go1.15 linux/amd64

Operating system / Environment

$ uname -a

Linux vic-linux-pc 5.8.0-2-MANJARO #1 SMP PREEMPT Sat Aug 8 17:55:27 UTC 2020 x86_64 GNU/Linux

Expected behavior

No errors, or solve this error.

Actual behavior

CI (GitHub Actions) send warnings and skip my code to master branch (but this code wasn't changed and works fine at lower version).

[ccojocar]

This is because https://golang.org/pkg/os/#File.Close returns and error which is not checked when calling defer. This was recently introduced to catch this kind of situation which could lead to a crash.

We should maybe rethink this rule since is a common pattern which might generate more headaches than catching security issues.

[koddr]

@ccojocar hi! Thanks for reply.

I think, better way to make it works, is skip defer ... lines from security checking. At this time, I (and other developers with the same problem) will still add a gosec comment to reset this line, so why not do it right away?

Because I have no idea, how to covering error with this language construction.

[ccojocar]

This is a solution.

You can use this code snippet to avoid the warning:

defer func() {
    if err := file.Close(); err != nil { 
         logger.Printf("Error closing file: %s\n", err)
    }
}()

[koddr]

Thanks, that works! 👍