Как снять блокировку PDF в ImageMagick на Arch Linux

ImageMagick’s security policy is blocking PDF to PNG conversion to prevent potential vulnerabilities in Ghostscript. On Arch Linux, you can resolve this by editing the security policy configuration file to allow PDF processing while maintaining overall security. The most direct solution is to modify the /etc/ImageMagick-7/policy.xml file to permit PDF operations.

Contents

• Understanding the Security Policy Block
• Solution 1: Modifying the Policy File
• Solution 2: Alternative Security Approaches
• Verifying the Fix
• Security Considerations
• Preventive Measures

Understanding the Security Policy Block

The error “attempt to perform an operation not allowed by the security policy `PDF’” occurs because Arch Linux’s ImageMagick installation includes security policies that block PDF processing. According to the Arch Linux bug report, this was implemented due to inherent security vulnerabilities in Ghostscript used for PDF interpretation.

The security concern stems from CVE-2018-10195 and related vulnerabilities where specially crafted PDF files could allow arbitrary code execution through Ghostscript. As noted in Stack Overflow discussions, distributions like Arch Linux implemented these restrictions following security researcher recommendations.

The problematic policy rule in your system appears as:

<policy domain="coder" rights="none" pattern="{PS,PS2,PS3,EPS,PDF,XPS}" />

This line explicitly denies read and write permissions for PDF and PostScript formats.

Solution 1: Modifying the Policy File

The most straightforward solution is to edit the ImageMagick policy configuration file:

Step 1: Open the policy file with administrator privileges:

sudo nano /etc/ImageMagick-7/policy.xml

Step 2: Locate the PDF restriction line and modify it. You have several options:

Option A: Comment out the entire restriction (simplest approach):

<!-- <policy domain="coder" rights="none" pattern="{PS,PS2,PS3,EPS,PDF,XPS}" /> -->

Option B: Change permissions to allow read and write operations:

<policy domain="coder" rights="read|write" pattern="{PS,PS2,PS3,EPS,PDF,XPS}" />

Option C: Create a more specific rule for PDF only:

<policy domain="coder" rights="read|write" pattern="PDF" />
<policy domain="coder" rights="none" pattern="{PS,PS2,PS3,EPS,XPS}" />

Step 3: Save the file and exit the editor.

Step 4: Test your conversion command:

convert -density 300 -depth 8 -quality 90 input.pdf output.png

As demonstrated in multiple troubleshooting guides, this approach immediately resolves the conversion block.

Solution 2: Alternative Security Approaches

If you prefer not to modify the global policy, consider these alternatives:

Update Ghostscript to the Latest Version

Security vulnerabilities were primarily addressed in newer Ghostscript versions. Ensure you have the latest version:

sudo pacman -Syu ghostscript

Use Delegate-Specific Policy

Some users report success by modifying only the Ghostscript delegate policy:

<policy domain="delegate" rights="read|write" pattern="gs" />

Implement Custom Policy Directory

For more granular control, you can create a custom policy directory and specify it at runtime:

mkdir -p ~/.config/ImageMagick-7/policy.xml
# Create custom policy file here
convert -policy-path ~/.config/ImageMagick-7/ -density 300 input.pdf output.png

Use Alternative Tools

Consider using specialized PDF conversion tools like pdftoppm or pdfimages for basic PDF extraction:

pdftoppm -png -singlefile input.pdf output

Verifying the Fix

After applying the policy changes, verify the fix with these commands:

Test basic PDF conversion:

convert input.pdf output.png

Check available PDF support:

identify -list format | grep PDF

Verify policy configuration:

convert -list policy | grep PDF

If the fix is successful, the conversion should complete without security policy errors, and the policy listing should show appropriate permissions for PDF files.

Security Considerations

While modifying the policy to allow PDF conversions, be aware of the security implications:

1. Source Trust: Only convert PDF files from trusted sources. Malicious PDFs could still exploit other vulnerabilities.

2. File Permissions: Ensure your user account has appropriate file permissions for the PDF files you’re converting.

3. Network Isolation: Consider performing PDF conversions in isolated environments when dealing with untrusted documents.

4. Regular Updates: Keep both ImageMagick and Ghostscript updated to benefit from the latest security patches.

As noted in the official ImageMagick security documentation, the security policy system is designed to balance functionality with protection against known exploits.

Preventive Measures

To minimize security risks while maintaining PDF conversion capabilities:

1. Use Sandboxing: Consider running PDF conversions in a sandboxed environment or container.

2. File Scanning: Scan PDF files with antivirus software before conversion.

3. Limited Permissions: Restrict ImageMagick to specific directories rather than system-wide access.

4. Audit Logs: Enable and monitor ImageMagick usage logs for suspicious activity.

5. Regular Policy Review: Periodically review your security policy configuration against the latest ImageMagick security advisories.

The Baeldung Linux guide provides additional insights into implementing sustainable security practices for ImageMagick deployments.

Sources

1. Stack Overflow - ImageMagick security policy ‘PDF’ blocking conversion
2. Arch Linux Bug Report - FS#60580
3. Linux Portal - Fix security policy errors in ImageMagick
4. ImageMagick Official Security Policy Documentation
5. Baeldung on Linux - Security Policies and ImageMagick Conversion Problems
6. Ask Ubuntu - imagemagick convert not allowed

Conclusion

To resolve the ImageMagick security policy blocking PDF to PNG conversion on Arch Linux, the most effective solution is to edit the /etc/ImageMagick-7/policy.xml file and modify or comment out the line that restricts PDF operations. This quick fix allows you to continue using PDF conversion while maintaining overall system security.

For ongoing security, consider updating Ghostscript regularly, implementing file scanning protocols, and using sandboxed environments for processing untrusted PDF documents. Always balance functionality needs with appropriate security measures for your specific use case.

If you encounter additional issues, verify both ImageMagick and Ghostscript versions, and consider consulting the official ImageMagick documentation for the latest security policy recommendations.