fix: Potential fix for code scanning alert no. 10: Uncontrolled data used in path expression

[skyoo2003]

Potential fix for https://github.com/skyoo2003/devcloud/security/code-scanning/10

General fix: validate untrusted path components as components (not full paths), reject absolute/empty/traversal-like segments, then build the full path and enforce containment using path semantics (filepath.Rel).

Best concrete fix here (in internal/services/s3/store.go):

1. Add a helper validatePathComponent(part string) error that rejects:
   • empty strings
   • "." and ".."
   • any path separator (/ or \)
2. In safePath, validate all parts first.
3. Replace the current HasPrefix containment check with:
   • cleanBase := filepath.Clean(fs.baseDir)
   • rel, err := filepath.Rel(cleanBase, cleaned)
   • reject when err != nil, rel == "..", or strings.HasPrefix(rel, ".."+string(filepath.Separator))
4. Keep existing behavior otherwise (same methods and return types), no changes needed in provider.go.

No new external dependencies are needed.

Suggested fixes powered by Copilot Autofix. Review carefully before merging.

[sourcery-ai]

Reviewer's Guide

Refines path handling in the S3 file store to validate each user-supplied path component and enforce directory containment using filepath semantics instead of prefix checks, mitigating path traversal risks flagged by code scanning alert #10.

File-Level Changes

Change	Details	Files
Introduce strict validation for individual path components before constructing filesystem paths.	Add validatePathComponent helper that rejects empty strings, ".", "..", and any component containing path separators Invoke validatePathComponent for every argument passed into safePath, returning an error on the first invalid component	internal/services/s3/store.go
Harden safePath directory containment logic using filepath.Clean and filepath.Rel instead of string prefix matching.	Normalize the base directory with filepath.Clean before path joining Build the joined path using the cleaned base directory and then clean the result Replace the HasPrefix-based containment check with a filepath.Rel-based check that rejects any path resolving outside the base directory (including traversal attempts)	internal/services/s3/store.go

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